Managingchangingsnowloadrisksfor buildingsinCanada’sNorth · CAN/CSA-S502-14 NationalStandardofCanada Managingchangingsnowloadrisksfor buildingsinCanada’sNorth Licensed for/Autorisé

CAN/CSA-S502-14National Standard of Canada

Managing changing snow load risks forbuildings in Canada’s North

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CAN/CSA-S502-14December 2014

Title: Managing changing snow load risks for buildings in Canada’s North

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Managing changing snow load risksfor buildings in Canada’s North

CAN/CSA-S502-14

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CAN/CSA-S502-14Managing changing snow load risks for buildings

in Canada’s North

December 2014 © 2014 CSA Group 1

ContentsTechnical Committee on Northern Built Infrastructure 3

Working Group on Changing Snow Loads in the North 5

Preface 6

0 Introduction 70.1 General 70.2 Overview 7

1 Scope 71.1 General 71.2 Exclusions 71.3 Terminology 8

2 Reference publications 8

3 Definitions 9

4 Snow overload planning and maintenance 104.1 General 104.2 Pre-season roof snow removal planning 104.2.1 General 104.2.2 Buildings already identified under snow overload watch programs 104.2.3 Snow removal plan 104.3 Building maintenance practices to reduce risk of collapse 114.3.1 Building modifications that increase risks 114.3.2 Maintenance practices 114.4 Roof snow monitors and their installation 114.5 Snow overloading risks accentuated by nearby higher buildings 124.6 Diversion of melt water from roof and building 124.7 Reducing sliding snow and ice 124.7.1 Snow guards 124.7.2 Restricted areas 124.8 Design changes 12

5 Detection, monitoring, and assessment of snow overloading risks for buildings 125.1 General 125.2 Monitoring snow conditions 135.3 Measuring snow on the ground in the community 135.3.1 General 135.3.2 Community snow measurements 135.3.3 Snow measurement equipment 135.3.4 Snow depth measurements 145.3.5 Snow water equivalent measurements 145.4 Assessment of risks from heavy snow conditions 145.4.1 General 14



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5.4.2 Detection of heavy snow conditions 155.4.3 Roof snow load inspections 155.4.4 Buildings already designated under snow overload watch programs 155.4.5 Building Documentation 155.5 Warning signs and responses to imminent risks for snow overloading 155.5.1 Warning signs 155.5.2 Building evacuation 165.5.3 Documentation 165.5.4 Marking of the building 165.5.5 Structural evaluation 165.6 Building classification and marking for snow overloading risks 165.6.1 General 165.6.2 “Unsafe” classification 175.6.3 “Safety uncertain” classification 175.6.4 “Safe” classification 17

6 Snow removal from roofs 176.1 Adverse weather conditions 176.2 Timing 186.3 Secured areas 186.4 Permafrost and drainage 186.5 Roof Hazards 186.6 Warning sounds 186.7 Safety considerations 186.7.1 Snow removal 186.7.2 Safety measures 186.7.3 Access 196.7.4 Removal sequence 196.8 Equipment 196.8.1 Rakes and shovels 196.8.2 Aerial lifts 196.9 Roof snow and ice removal procedures 196.9.1 Work zones 196.9.2 Sequence 196.9.3 Limitations 20

Annex A (normative) — Commentary 22Annex B (informative) — Buildings at greatest risk of snow overload roof collapse 26Annex C (informative) — Snow accumulation measurements 28Annex D (informative) — Building access markings 32Annex E (informative) — Assessment form 37Annex F (informative) — Snow loads, climate change and buildings: A Discussion 46Annex G (informative) — Sample advisory on snow overload conditions 62



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Technical Committee on Northern BuiltInfrastructure

S. Brown Northwest Territories Association of Communities(NWTAC),Yellowknife, Northwest TerritoriesCategory: Owner/Operator/Producer

Chair

J. Streicker City of Whitehorse,Whitehorse, YukonCategory: General Interest

Vice-Chair

H. Auld Risk Sciences International,Ottawa, OntarioCategory: Supplier/Contractor/Consultant Interest

S. Dueck Yukon Government Community Services,Whitehorse, YukonCategory: Regulatory Authority

D.W. Hayley Hayley Arctic Geoconsulting,Kelowna, British ColumbiaCategory: Supplier/Contractor/Consultant Interest

K.R. Johnson Stantec Consulting Ltd.,Edmonton, AlbertaCategory: Supplier/Contractor/Consultant Interest

C. Larrivée OURANOS Impacts & Adaptation,Montréal, Québec

Associate

O. Lee Government of the Northwest Territories,Yellowknife, Northwest TerritoriesCategory: Owner/Operator/Producer

N. Pisco Governnment of Nunavut Dept of CommunityServices,Iqaluit, NunavutCategory: Owner/Operator/Producer

B. Roy Dept of Community & Government Services,Government of Nunavut,Pond Inlet, NunavutCategory: Regulatory Authority



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T. Sheldon Nunatsiavut Department of Lands and NaturalResources,Nain, Newfoundland and LabradorCategory: Regulatory Authority

E. Sparling Risk Sciences International,Ottawa, Ontario

Associate

G. Strong Dillon Consulting Limited,Yellowknife, Northwest TerritoriesCategory: Supplier/Contractor/Consultant Interest

R. Trimble Tetra Tech EBA,Whitehorse, Yukon

Associate

R. Van Dijken Council of Yukon First Nations,Whitehorse, YukonCategory: General Interest

M. Westlake Aboriginal Affairs and Northern Development Canada(AADNC),Gatineau, QuébecCategory: Regulatory Authority

M. Braiter CSA Group,Mississauga, Ontario

Project Manager



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Working Group on Changing Snow Loads inthe North

H. Auld Risk Sciences International,Ottawa, Ontario

Chair

R. Dennill Northwest Territories Association of Communities(NWTAC),Yellowknife, Northwest Territories

S. Dueck Yukon Government Community Services,Whitehorse, Yukon

P.L. Jarrett Environment Canada,Toronto, Ontario

K. Kumi Governnment of Nunavut Dept of CommunityServices,Iqaluit, Nunavut

T. Livingston Williams Engineering Canada Inc.,Yellowknife, Northwest Territories

S. Mooney Yukon College,Whitehorse, Yukon

P. Nolan StructureAll Ltd,Yellowknife, Northwest Territories

W. Wyness Northwest Territories Association of Architects,Yellowknife, Northwest Territories

D. Torrey CSA Group,Mississauga, Ontario

Project Manager



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PrefaceThis is the first edition of CAN/CSA-S502, Managing changing snow load risks for buildings in Canada’sNorth.

The objective of this Standard is to inform communities on measures for safe roof snow removal fromexisting buildings and for protection of building occupants and assets from overloading risks due toincreasing accumulations and weights. Procedures that can reduce risks for roof and building collapsesare outlined, including procedures for monitoring heavy snow and ice accumulations, safe removal ofsnow on roofs when needed, and for maintenance and snow removal planning.

CSA Group received funding for the development of this Standard from Standards Council of Canada, aspart of the Northern Infrastructure Standardization Initiative, supported by the Government of Canada’sClean Air Agenda.

This Standard was prepared by the Working Group on Changing Snow Loads in the North, under thejurisdiction of the Technical Committee on Northern Built Infrastructure and the Strategic SteeringCommittee on Construction and Civil Infrastructure, and has been formally approved by the TechnicalCommittee. This Standard has been approved as a National Standard of Canada by the StandardsCouncil of Canada.Notes:1) Use of the singular does not exclude the plural (and vice versa) when the sense allows.2) Although the intended primary application of this Standard is stated in its Scope, it is important to note that it

remains the responsibility of the users of the Standard to judge its suitability for their particular purpose.3) This Standard was developed by consensus, which is defined by CSA Policy governing standardization — Code

of good practice for standardization as “substantial agreement. Consensus implies much more than a simplemajority, but not necessarily unanimity”. It is consistent with this definition that a member may be included inthe Technical Committee list and yet not be in full agreement with all clauses of this Standard.

4) To submit a request for interpretation of this Standard, please send the following information [email protected] and include “Request for interpretation” in the subject line:a) define the problem, making reference to the specific clause, and, where appropriate, include an

illustrative sketch;b) provide an explanation of circumstances surrounding the actual field condition; andc) where possible, phrase the request in such a way that a specific “yes” or “no” answer will address the

issue.Committee interpretations are processed in accordance with the CSA Directives and guidelines governingstandardization and are available on the Current Standards Activities page at standardsactivities.csa.ca.

5) This Standard is subject to a review within five years from the date of publication. Suggestions for itsimprovement will be referred to the appropriate committee. To submit a proposal for change, please send thefollowing information to [email protected] and include “Proposal for change” in the subject line:a) Standard designation (number);b) relevant clause, table, and/or figure number;c) wording of the proposed change; andd) rationale for the change.



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CAN/CSA-S502-14Managing changing snow load risks forbuildings in Canada’s North

0 Introduction

0.1 GeneralAs climate conditions continue changing, Northern communities need to be prepared to deal with theimpacts arising from increases in snow weights (loads) on existing buildings.

Snow can impact buildings in many ways. When the weight of the snow on the roof of a buildingapproaches or exceeds its original design capacity to withstand heavy snow conditions, a condition ofsnow “overloading” is reached that poses risks for building roof collapse and the safety of buildingoccupants and critical assets that are part of a building (e.g., communications equipment). In addition toincreased risks for collapse of roofs, snow on the roof can cause water leakage (from ice dams) whichcan lead to structural concerns and health risks from mould as well as slip and fall hazards near thebuilding. An abundance of snow around buildings can also lead to increased snow removal expendituresand hinder access to and egress from buildings, access to water and sewer services, and buildingmaintenance.

0.2 OverviewThis Standard is intended to be used to establish ongoing practices to reduce snow overloading risksover the lifespan of the building, which include pre-season roof snow removal planning and buildingmaintenance to reduce risks of collapse and extend the life of the roof.

In addition to the assessment and removal requirements outlined in the body of this Standard, a seriesof Annexes have been included to provide additional information and templates for the user.

To assist in application of this Standard, a snow load assessment flowchart has been provided inFigure 1.

1 Scope

1.1 GeneralThis Standard providesa) maintenance procedures to reduce snow overload risk on existing buildings;b) monitoring, detection, and assessment methods for snow load risks on buildings; andc) procedures for snow removal.

1.2 ExclusionsThis Standard does not addressa) specific requirements for the design or construction of new buildings subjected to snow loads; orb) requirements for the structural rehabilitation or decommissioning of buildings subjected to critical

snow overloading risks.



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Note: Although provisions in the building codes apply for new design, Annex F provides supplementary backgroundinformation on climate change and its implications on the design and retrofit of buildings.

1.3 TerminologyIn CSA Standards, “shall” is used to express a requirement, i.e., a provision that the user is obliged tosatisfy in order to comply with the standard; “should” is used to express a recommendation or thatwhich is advised but not required; “may” is used to express an option or that which is permissiblewithin the limits of the standard; and “can” is used to express possibility or capability.

Notes accompanying clauses do not include requirements or alternative requirements; the purpose of anote accompanying a clause is to separate from the text explanatory or informative material.

Notes to tables and figures are considered part of the table or figure and may be written asrequirements.

Annexes are designated normative (mandatory) or informative (non-mandatory) to define theirapplication.

2 Reference publicationsThis Standard refers to the following publications, and where such reference is made, it is to the editionlisted below, including all amendments published thereto.

CSA GroupCAN/CSA-S500-14Thermosyphon foundations for buildings in permafrost regions

CAN/CSA-S501-14Moderating the effects of permafrost degradation on existing building foundations

CAN/CSA-S503-15Community drainage system planning, design, and maintenance in northern communities

PLUS 4011-10Technical guide — Infrastructure in permafrost: A guideline for climate change adaptation

Z1002-12Occupational health and safety — Hazard identification and elimination and risk assessment and control

ASTM International (American Society for Testing and Materials)D698-12e1Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort(12 400 ft-lbf/ft3 (600 kN-m/m3))

Other publicationsNational Building Code of Canada 2015 (“NBCC”), National Research Council of Canada, Ottawa.

Good Building Guidelines (2nd edition), 2005. Community and Government Services, Government ofNunavut, Iqaluit.



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Good Building Practices for Northern Facilities (3rd edition), 2011. Department of Public Works andServices, Government of the Northwest Territories, Yellowknife.

Good Building Practices for Northern Facilities (3rd edition), 2011. Government of the Yukon,Whitehorse.

Newark, M.J., Welsh, L.E., Morris, R.J., and Dnes,W.V., 1989: Revised ground snow loads for the 1990National Building Code of Canada. Canadian Journal of Civil Engineering, 16, 267–278.

3 DefinitionsThe following definitions shall apply in this Standard:

Classification — the determination of the safety rating of a building or zone.

Climate normals — the average value of a climate variable or parameter over a fixed period.Notes:1) Typical climate normals are the average value of a climate variable over 30 years.2) Currently available climate normals refer to the period 1981–2010. Thus, the normal snowfall is the mean or

average value for the 1981-2010 period.

Competent individual — a person who through training, qualification, and experience has acquired theknowledge and skills necessary for undertaking tasks assigned to him or her.Notes:1) In many Northern Communities, maintenance staff employed by the local authority having jurisdiction will

perform the duties of evaluating the snow overloading risk as well as undertaking the removal of snow whenit is determined to be necessary.

2) For more information on competent individuals with regards to building evaluation, see Annex F.

Engineer — a professional engineer experienced with design of buildings and registered with theAssociation of Professional Engineers in the jurisdiction where the project is located.

Freezing rain — precipitation that falls as liquid rain and freezes upon contact with surfaces such assidewalks, roads, and trees.

Load — the force acting on an object.

Local knowledge — the historical information available in a community.

Overloading — loading that exceeds the intended design capacity.

Sampling tube — a calibrated tool used to establish snow weight.

Snow weight — the weight of snow, measured using a standard snow sampling tube.

Snow depth — the total depth of snow on the ground determined by making a series of measurementsand taking the average.Notes:1) The area selected for measurement is chosen with the view to avoid drifts.2) Care is to be taken to ensure the total depth is measured including the depth of any layers of ice.

Snow overload watch building — a building that has been identified as a higher risk of collapse whencompared to other buildings in the community.Note: The snow overload watch designation is typically conducted by a competent individual.



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Snow survey — a manual measurement of the snow depth and snow water equivalent at a site.Note: Samples are taken at several pre-determined points at a snow course or snow pillow site. For a morecomplete description see Annex D.

Snow water equivalent — the water content or depth of a layer of water having the same mass andupper area as its snowpack and usually measured in millimetres (i.e., the equivalent to the water thatwould result upon melting of the depth of the snow on the ground).Note: An example would be if the snow covering a given area has a water equivalent of 50 cm, then a standardcolumn of the snow would melt into a pool of water 50 cm deep covering the same column area.

Snowpack — layers of snow that have accumulated over the course of the snow season at a givenlocation.

4 Snow overload planning and maintenance

4.1 GeneralMany maintenance and pre-season snow removal planning practices will help to reduce risks of snowoverloading on buildings and contribute to a longer lifespan and serviceability of the building.Notes:1) Annex F includes considerations on increasing snow loads, climate change, and new building design.2) Guidance on design considerations to reduce risks from snow overloading on new buildings can also be found

in the Good Building Practice for Northern Facilities, developed by the Government of Northwest Territories.These design considerations include the use of simple and uncomplicated roof shapes to minimize snow andice accumulations on the roof and the selection of roofing materials to shed snow (e.g., metal).

3) In most Northern communities, spring thaw and snow melt arrives quickly, requiring immediate response.Further information and procedures for managing community drainage risks is provided in CAN/CSA-S503.

4.2 Pre-season roof snow removal planning

4.2.1 GeneralBefore the start of the snow season, a building snow removal plan shall be developed by the buildingowner, manager, and competent individuals according to Clause 4.2.3. This plan shall describe themethod for snow removal from the roof of the building during heavy snow winters. A copy of the planshall be stored in an offsite location, and updated a minimum of every 5 years or after significantadditions/changes have been made to the roof.

4.2.2 Buildings already identified under snow overload watch programsIf a building has already been designated as a snow overload watch building due to existing overloadconcerns, a risk assessment should be prioritized and used to develop a snow removal plan.Note: For some specific buildings, the engineering assessment may need to include measures to reinforce thebuilding.

4.2.3 Snow removal planThe snow removal plan should establisha) whether snow can be safely removed from the roof in a timely manner by competent individuals;b) the competent individual who will carry out roof snow removal;c) the sequence for snow removal, including associated risks;d) that the snow removal plan does not create additional unbalanced snow loads;



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e) that occupational health and safety and fall protection requirements have been implemented;f) any structural evaluations that should be considered to develop a plan for long-term remedial

action when a roof has required frequent snow/ice removal; andg) barrier placement to protect the public, if required.Notes:1) See Annex E for a sample snowfall roof assessment form that may be developed as part of the snow removal

plan.2) See Clause 6.3 for safe removal of snow from roofs.3) The use of salt should be avoided on most roofs.

4.3 Building maintenance practices to reduce risk of collapse

4.3.1 Building modifications that increase risksPractices that increase snow overloading risks that should be avoided includea) re-roofing over three or more layers of shingles;b) modifications to the structure that cause weakening of the roof’s load tolerances; and

Note: A roof in an older building could also be “under-built” and more vulnerable to structural problems.These deficiencies, combined with excessive loading, can lead to potential for roof collapse.

c) adding mechanical units, additional insulation, antennae, solar panels, or other equipment to theroof without proper assessment or reinforcement.

4.3.2 Maintenance practices

4.3.2.1 Inspection and reportingBuilding maintenance should be practiced to reduce risks of roof degradation and collapse, and includeat a minimum, annual inspection and condition reporting ofa) the roof and make necessary repairs as soon as possible;b) flashing and roof parapets for damage from previous snow loads and repair as soon as possible;c) metal members and connectors on roofs (especially older roofs) for corrosion and reinforce, as

necessary;d) areas of previous ice build up to identify solutions to prevent future issues; ande) check for any visually apparent deflection of roof framing members or unexplained cracks in the

building and seek expertise from a competent individual where this is present.

4.3.2.2 DocumentationAll building changes and maintenance actions taken over the lifespan should be documented.Notes:1) Documentation of maintenance practices and changes will be required for any additional risk assessments or

structural evaluations of the building.2) Annex E provides a sample template and tool that can be used for a building inspection.

4.4 Roof snow monitors and their installationIn communities where increasing snow loads are expected to result in periodic snow clearing from theroof of a building (i.e., snow accumulations and weights are increasing), a structural deformationmonitoring system may be considered to provide earlier alerts on when snow removal actions areneeded.Notes:1) Roof monitoring systems may be considered for construction of new buildings in communities where snow

loads are increasing or expected to increase.



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2) Buildings that have been assessed as being at risk from snow overloading or designated under snow overloadwatch programs may consider the installation of roof snow monitoring instrumentation, particularly when theroof of the building is being renovated, repaired, or replaced.

4.5 Snow overloading risks accentuated by nearby higher buildingsBuildings with lower level roofs relative to another higher building in its vicinity may require anengineering structural evaluation and reinforcing to higher snow loads after the addition of the nearbyhigher building.

4.6 Diversion of melt water from roof and buildingSurface water from roof snowmelt, ice melt, and spring rainfall should be diverted away from buildingsand into effective community drainage sources.Notes:1) Care should be taken to prevent blockage of drains.2) Further information and procedures for managing community drainage risks is provided in CAN/CSA-S503.3) Drainage of roofs should be done so as to divert water away from the building foundation. See CAN/CSA-S501

for information on permafrost degradation.

4.7 Reducing sliding snow and ice

4.7.1 Snow guardsThe use of roof snow guards to retain snow and ice at the edge or peak may be considered to preventlarge amounts of snow sliding froma) a higher level roof to a lower level roof, causing potential overloading; orb) slippery roofing materials or steep slopes onto the ground below where it can create hazards on

the ground below for pedestrians and occupants entering and leaving the buildings.

4.7.2 Restricted areasThe building snow risk plan should identify areas for restricted access below roofs where massed chunksof ice and snow tend to accumulate and fall. Access should be restricted to prevent injury.

4.8 Design changesWhen changes or additions are made to a building that may affect its structural integrity, structuralevaluations should be undertaken to assess the changes and verify that the original snow load designhas not been compromised by additional loads placed on the roof (e.g., equipment, suspendedmechanical structures such as conveyers).

5 Detection, monitoring, and assessment of snow overloading risks forbuildings

5.1 GeneralRoof overload conditions are related to ground snow loads. Measurements of snow conditions shouldbe conducted to determine the level of snow overloading risks posed to many of the buildings in acommunity, particularly during heavy snow winters.



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5.2 Monitoring snow conditionsCommunities should monitor snow accumulations througha) local knowledge of snow conditions that indicates unusually high snow depths or heavy snow

weights, typically spanning 30 years;b) measurements taken near the community by agencies, provided that the snow conditions at the

agency measurement site are representative of snow conditions in the community;Note: Typically, snow measurements are taken by territorial, provincial, federal, municipal, water agency, andother organizations.

c) community measurements of snow depths or snow water equivalents taken by the community at aconsistent location each winter using the practices described in Annex C.

5.3 Measuring snow on the ground in the community

5.3.1 GeneralCommunity snow measurements provide valuable guidance needed to determine the relative severityof the heavy snow conditions, the needs for roof snow removal, and the potential risks for roofcollapses.

5.3.2 Community snow measurements

5.3.2.1 GeneralWhen local knowledge indicates that snow depths are unusually high or snow conditions are unusuallyheavy, communities should undertake measurements of the snow depths or snowpack waterequivalents, according to Clause 5.3.4.Note: See Annex C for descriptions of snow measurements and procedures.

5.3.2.2 Location selectionCommunity snow measurements should be eithera) observed at a selected location in the community consistently from year to year; orb) based on nearby official snow measurements taken by various agencies if snow conditions at the

official site are representative of the community snow conditions.Note: Annex F includes observed trends in snow, other precipitation, and in temperatures.

5.3.2.3 FrequencySnow measurements shall be taken a minimum of once per day during active and significant snowfall orrain on snow events.

5.3.3 Snow measurement equipmentCommunity snow measurements shall includea) a graduated measuring stake to determine the initial depth of the accumulated snow on the

ground; andb) a standard snow sampling tube to conduct manual snow surveys of snow water equivalent,

obtained by weighing a column of snow collected.Notes:1) Measurements from some remotely-sensed or automatic snow measurements may be subject to significant

uncertainty and likely will require meteorological expertise for their interpretation (e.g., automatic snowdepth data).



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2) While snowpack depths are relatively easy to measure, snow water equivalent measurements are somewhatmore difficult but provide important additional information for snow overloading. Snow water equivalentmeasurements, as outlined in Annex C, indicate the actual weight of the snow on the ground.

5.3.4 Snow depth measurements

5.3.4.1 Site of snow depth measurementsSnow depth measurement readings shall be taken at a level site in the community not subjected tosignificant snow drifting.Note: For typical causes of snow drifting around and on buildings, see Figure A.1.

5.3.4.2 Measurement proceduresA minimum of 3 snow depth measurements shall be taken in the vicinity of the stake location and awayfrom pronounced snow drifts. The values shall be averaged to obtain a single snow depth measurementfor the community.

5.3.4.3 Measurement documentationIn addition to the snow depth, the date, time, and location shall be recorded along with notes on anyother influences on the snow conditions (e.g., nearby snow drifts, crusty snow, ice near the ground, etc).

5.3.5 Snow water equivalent measurements

5.3.5.1 Site of snow water equivalent measurementsSnow water equivalent measurements shall be taken at a level site in the community not subjected tosignificant snow drifting.Note: Refer to Annex C for further on measurement procedures.

5.3.5.2 Measurement equipmentThe snow water equivalent shall be measured using a standard snow sampling tube or alternativedevice.

5.3.5.3 Measurement proceduresA minimum of 5 snow core samples shall be taken in the vicinity of the selected snow monitoring siteand away from pronounced snow drifts. The values shall be averaged to obtain a single snow waterequivalent measurement for the community.

5.3.5.4 Measurement documentationIn addition to the snow water equivalent, the date, time, and location shall be recorded along withnotes on any other influences on the snow conditions (e.g., nearby snow drifts, crusty snow, ice nearthe ground, etc).Note: See Annex E for a sample building assessment form that may be used to record snow data.

5.4 Assessment of risks from heavy snow conditions

5.4.1 GeneralHeavier snow conditions pose variable risks for building snow overloading and roof collapses in thecommunity. Typically, buildings that were designed using lower snow load (weight) values or poorlymaintained roofs will be most at risk.



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5.4.2 Detection of heavy snow conditionsSnow conditions shall be classified as heavy when community ground snow measurements indicateconditions that are approaching potential failure or collapse thresholds.Note: Potential failure thresholds vary from one building to the next and are related, in part, to the snow loadconditions used at the time of construction of a building and to the roof maintenance practices.

5.4.3 Roof snow load inspectionsWhen heavy snow conditions are detected in a community, competent individuals shall conduct apreliminary snow overload inspection of each building and carefully note any audible and visiblyapparent warning signs indicating potential risks roof collapse, as outlined in Clause 5.6.2.Notes:1) Refer to Annex E for a sample checklist and template that can be used for building snow overloading

inspections.2) Blockage of roof top equipment due to snow drifting should also be noted due to the potential impact on

functionality of equipment and egress issues. See Figure A.1.

5.4.4 Buildings already designated under snow overload watch programsBuildings already assessed as being at risk for snow overloading and designated under snow overloadwatch criteria should be inspected periodically during each snow season and daily during heavy snowevents.

5.4.5 Building Documentation

5.4.5.1 GeneralThe competent individual shall assemble documentation on the specific building to support the riskassessment process and to inform decisions on any need for building reinforcement.

5.4.5.2 Documentation informationBuilding documentation should includea) building age;b) building drawings at the time of design and construction;c) roof snow load design criteria;d) additional equipment and loads added to the roof;e) mobile equipment on the roof that could be removed safely;f) roof repair and maintenance records;g) renovations and changes that could have impacted building capacity to withstand snow loads;h) roof materials used; andi) history of moisture leaks.Note: A sample assessment form is included in Annex E.

5.5 Warning signs and responses to imminent risks for snow overloading

5.5.1 Warning signsWarning signs shall be noted during the building and roof inspection, and may includea) sagging roof;b) new and severe roof leaks;c) cracked or split wood members;d) bends or ripples in supports such as columns or open web steel joists;



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e) new and sudden cracks in walls or masonry;f) sheared off screws from steel frames;g) sprinkler heads that have dropped down below ceiling tiles;h) doors that newly pop open or suddenly will not close;i) doors or windows that are suddenly difficult to open;j) bowed utility pipes or conduit attached at ceiling; andk) creaking, groaning, cracking, or popping sounds.Note: For additional information and visual examples of warning signs, see Annex B.

5.5.2 Building evacuationBased on the number and intensity of the observed warning signs of roof snow overload and potentialrisk of collapse, the competent individual shall evaluate whether immediate building evacuation isprudent.

5.5.3 DocumentationIf safe to do so, the competent individual shall provide building condition documentation as outlined inClause 5.4.5.2 to support an engineering structural evaluation and to inform decisions on any need forbuilding reinforcement.Note: A sample evaluation form for documenting building condition can be found in Annex E.

5.5.4 Marking of the buildingBuilding owners, managers, or competent individuals should mark a building as unsafe and restrictaccess according to Clause 5.6 until an engineering risk assessment has determined that the building issafe for occupancy.

5.5.5 Structural evaluationA structural evaluation for snow overloading shall be undertaken immediately by an engineer uponnoting warning signs of potential roof collapse risk. If an engineering risk assessment cannot beundertaken immediately, the building should remain closed until measures are taken to verify that thebuilding is safe.

5.6 Building classification and marking for snow overloading risks

5.6.1 GeneralActing upon results of the building inspection, the competent individual shall, at a minimum, rank thebuilding snow overload risk as “unsafe”, “safety unknown”, or “safe”, in accordance with Clauses 5.6.2through 5.6.4, as follows:a) “Unsafe” — access to occupants and non-essential personnel should be prohibited and the building

recommended for structural evaluation;b) “Safety uncertain” — access to occupants should be prohibited and the building recommended for

structural evaluation; orc) “Safe” — access to occupants is permitted;Notes:1) Annex D provides information and options for building marking methods.2) The safety classification of the building is typically designated by coloured markings. Red markings indicate

“unsafe” buildings, amber markings indicate “safety uncertain”, and green markings indicate “safe” buildings.



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5.6.2 “Unsafe” classification

5.6.2.1 Unsafe snow overloading conditionsIf the estimated snow loads on the roof approach or exceed design snow load values and the inspectionindicates warning signs, the building shall be classified as “Unsafe”.Note: See Clause 5.5.1 for typical warning signs.

5.6.2.2 Immediate actionsUnder guidance from a competent individual, the building owner, or manager should considerimmediate actions, includinga) evacuation of the building or parts of the building;b) structural evaluation by an engineer; orc) snow removal.

5.6.2.3 Building closure for “unsafe” snow overload conditionsIf a competent individual has any doubt about the integrity of a roof under heavy snow conditions, thebuilding or a portion of the building should be evacuated until a building assessment can be soughtusing a competent individual.

5.6.2.4 Marking for “unsafe” buildingsTo ensure that entry restrictions are observed, colour-coded markings should be affixed to access pointsof an affected building.Note: Safety rating markings indicate that a building has been inspected.

5.6.2.5 Structural evaluationA structural evaluation shall be undertaken by a competent individual to indicate whether it is safe toallow personnel on or under the roof, to provide a plan for clearing snow from the roof, and todetermine whether additional reinforcing is required before snow removal.

5.6.3 “Safety uncertain” classificationA building shall be classified “Safety uncertain” if there is reasonable doubt about the safety ofoccupants due to snow overloading risks. General access should be restricted, but limited access may begranted until a structural evaluation of at-risk buildings review is conducted.

5.6.4 “Safe” classificationIf the actual snow load is likely well below the critical design snow load and the inspection does notindicate concerns, the building may be classified as “Safe”.

6 Snow removal from roofs

6.1 Adverse weather conditionsFor safety reasons, snow removal should not be undertaken during a blizzard, snow storm, or otheradverse weather conditions.Note: The safe removal of snow from a roof is a difficult and dangerous task that requires careful attention tosafety, expertise, and reasonable work conditions. Workers are at risk of being killed or seriously injured whileremoving snow or ice from roofs.



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6.2 TimingIf there are no adverse visual and audible warning signs of potential roof collapse and heavy communitysnow conditions are observed, the competent individual should consider removing snow from the roof.Note: For unusually heavy (extreme) snow conditions, a structural evaluation may be required ensure that snowremoval is safe.

6.3 Secured areasAreas onto which snow will be dumped from a roof shall be secured and marked, if necessary, toprotect pedestrians and prevent access to the building.

6.4 Permafrost and drainageSnow removed from the roof shall not be placed near the foundation of the building and shall be storedat a community approved storage location well away from the building in order to prevent permafrostdegradation and drainage issues.Note: See CAN/CSA-S500, CAN/CSA-S501, CAN/CSA-S503, and CSA PLUS 4011.

6.5 Roof HazardsPersonnel removing roof snow shall take note whether there are any hazards on the roof that might behidden by the snow and need to be marked as trip hazards, including roof drains, skylights, vents, andother equipment.

6.6 Warning soundsSnow removal personnel should always use caution by remaining alert to unexpected sounds ormovement around surfaces that have been weighed down by snow (or water from melted snow),because these surfaces could collapse.

6.7 Safety considerations

6.7.1 Snow removalSnow removal shall be conducted under the direction of a competent individual.

6.7.2 Safety measuresPersonnel accessing roofs and other elevated surfaces to clear snow should adhere to the followingsafety measures:a) Ensure that personnel are trained on fall hazards and the proper use of fall protection equipment;b) Ensure that personnel use fall protection equipment in areas not adequately guarded;c) Instruct personnel who wear personal fall protection equipment to put on their harnesses and

buckle them snugly before reaching the roof;d) Remove or clearly mark features on the roof that could become trip or other hazards;e) Have a plan for rescuing any fallen colleagues caught by the fall protection system; andf) Use extreme caution when working near power lines or electrical equipment and maintain a

distance of at least 3 m away from any power line.Notes:1) Refer to applicable safety acts and regulations for the location of the building for guidance on proper

protective measures.2) Contractors are expected to follow safety rules and regulations, receive training in roof snow removal, and

have adequate levels of insurance for both workers compensation and general liability coverage for propertydamage or bodily injuries caused by contractor’s employees or their operations.



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6.7.3 AccessWhenever possible, personnel should use methods to clear ice and snow without going onto the roof,including the use of ladders, snow rakes or drag lines from the ground, or use aerial lifts if available.

6.7.4 Removal sequenceTo reduce the risk of creating an unbalanced load on the roof, procedures for removing snow from acomponent of the roof should ensure thata) snow should be removed in small amounts at a time;b) snow is removed uniformly across the roof; andc) removal should avoid the creation of snow piles on the roof.

6.8 Equipment

6.8.1 Rakes and shovels

6.8.1.1When using snow rakes, personnel should use extendable, nonconductive poles and designatepersonnel as “monitors” to ensure that a distance of 3 m is maintained between the snow rake and anyoverhead power lines.

6.8.1.2When using snow shovels, they should be constructed of plastic.

6.8.1.3When working at height, rakes and shovels shall only be used when personnel are supported inaccordance with the safety act and regulations.

6.8.2 Aerial liftsWhen aerial lifts are used, a minimum clearance of at least 3 m should be maintained away from thenearest energized overhead power lines.

6.9 Roof snow and ice removal procedures

6.9.1 Work zonesTo avoid risk of injury or suffocation from falling roof snow, personnel standing on the ground removingsnow from the roof shoulda) mark a safe work zone where snow is to be removed; andb) wear protective eye and head protection, especially when the snow load includes ice or hard

packed snow.

6.9.2 SequenceSnow removal should be considered to reduce risks of collapse and damage to the roof, and beperformed in the following order:a) Remove drifted snow;

Note: Drifted snow will generally be found on lower roofs, but can also occur around rooftop mechanicalvents, skylights, parapet walls, and around penthouse walls. See Figure A.1 for an illustration of typical snowdrift.

b) Remove snow from the middle of the bays;



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Notes:1) If a building has 15–20 m bays with the primary steel running from the peak to the eave, the snow

should be removed from the centre of the bay starting at the peak and working toward the eave.2) The greatest deflection can be expected at the centre of the bay. This should be repeated for all the

bays.c) Remove snow evenly from both sides of the roof so that the load on one side of the roof is not

significantly greater than the other side; andd) For peaked roofs, the snow should be removed from the centre of a given bay on one side of the

roof and then removed on the same bay on the other side of the ridge or peak.

6.9.3 LimitationsThe following limitations should be observed:a) snow from upper roofs should not be piled onto lower roofs;b) when removing snow and/or ice accumulation from the roof, avoid removal within 5 cm of the top

surface of the roof to avoid damage to the roof membrane; andc) when removing snow from one section of a roof, avoid travelling on and compacting snow on

adjacent roof sections.



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Figure 1Snow load assessment flowchart

(See Clause 0.2.)

Overview /IntroductionClauses 1 – 4

Snow falls andaccumulates

Measure snowfallClause 5.3

Assessaccumulated

snowfallClause 5.4

Is therea concern for

public safety dueto snowlevels?

Building stays openContinue to

monitor snowaccumulation

Can snow besafely removed?

Qualified personnelreviews building

Clause 5.6

Is the buildingstructurally safe for

continued use?

Remove snowfrom building

Clause 6

Assess if snowcan be safely

removedClause 5.6

Mark unsafe areasfor restricted

accessClause 5.6

Is thebuilding safe for

continueduse?

Assess building forcontinued use

Clause 5.5

Building closedfor repairClause 5.6

No

Yes

No Yes

No

No Yes

Yes



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Annex A (normative)CommentaryNote: This Annex is not a mandatory part of this Standard.

A.1 IntroductionWith increasing snow loads due to climate change, roof collapse is becoming a frequently occurringscenario. Increasing snow loads are a key area of concern for not only designers of new structures, butfor owners of existing buildings that are suffering roof failures and other structural problems.

Failures are typically caused by a combination of events, including snow loads that exceed design andbuilding condition. Critical snow overload risks can result from increased depths, increased densities,snow drifts, rain soaked snow, and unbalanced snow. Building condition contributing to higher risksincludes improper maintenance, inadequate design, construction errors, and improper snow removal.

Although snow load increases cannot be mitigated, proper planning, maintenance, assessment, andsnow removal procedures can significantly reduce the risk of roof collapse.

A.2 Snow load types

A.2.1 GeneralIncreased snow depth, snow drifts, rain soaked snow, and unbalanced snow are common causes of roofcollapse due to snow.

A.2.2 Drifting snowDrifting snow results from snow that has been carried by wind and deposited in a location due tochange in geometry. Causes of drifting includea) roof elevation changes;b) parapet walls;c) gable roofs; andd) rooftop equipment.

Common causes of drifting on roofs can be found in Figure A.1.



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Figure A.1Snow drifting

(See Clauses 5.3.4.1, 5.4.3, 6.9.2, and A.2.2.)

Solar panels

Parapet

Blocked door

Buried HVAC equipment

Firewall

Buried plumbing vent

Penthouse

Blocked air intake

Blocked doorBlocked accessto loading doors

Roof vents

A.2.3 Sliding snow and iceSliding snow and ice can provide a risk to roof integrity and danger to the public (see Figure A.2). Whensnow slides from a high roof onto a roof below, overloading of the lower roof can occur. In addition,sliding snow and ice can dislodge roof elements or unevenly load roofs.

Figure A.2Sliding snow and ice(See Clause A.2.3.)

A.2.4 Other conditionsIce dams typically form on the eaves, where thawed water from heated sections of the roof refreeze atthe uninsulated eave.



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A.3 Snow loading risks

A.3.1 GeneralWhen heavy snow events occur, they can result in loads exceeding the allowable capacity of thestructure. However, there are other factors that can increase the likelihood of a snow-induced failure.This can include roof capacity, building deterioration, roof shape, or roof obstructions.

A.3.2 Roof capacityRoofs are typically constructed to capacities established by building codes. As climatic data has changedover the years, so has the minimum required design criterion. A building designed in the 1950’s mighthave been designed to resist less snow load than a building built to the current code. Guidance ofdetermination of roof capacities can be found in Annex F.

A.3.3 Building deteriorationAs buildings deteriorate, they become more susceptible to roof failure. Poorly maintained roofing,insulation, fasteners, and flashing can result in reduced roof capacity.

A.3.4 Roof shapeRoof shape and obstructions can create drifting and loading conditions. Irregular roofs should be closelymonitored during heavy snow falls. Drift conditions can form quickly and need regular monitoring.

A.4 Planning for the snow eventMany maintenance and pre-season snow removal planning practices can help to reduce risks of snowoverloading on buildings. Before the start of the snow season, snow removal plans can be developed inadvance of the snow season, describing the method for snow removal from the roof of the buildingduring heavy snow winters. The snow removal plan is particularly important for buildings that havebeen identified as being at high snow overload risk.

Information on planning for the event can be found in Clause 4.

A.5 Monitoring, detecting, and assessing snow risksMeasurements of snow conditions are critical to helping determine the level of snow overloading risksposed to many of the buildings in a community, particularly during heavy snow winters. Communitiesshould monitor snow accumulations each winter through local knowledge of snow conditions spanningat least 30 years, measurements taken near the community by different agencies, and communitymeasurements of snow water equivalents at consistent locations each winter.

Information on monitoring, detecting, and assessing snow risks can be found in Clause 5.

A.6 Snow removalIf there are no adverse visual or audible warning signs of potential roof collapse after heavy communitysnow conditions are observed, roof snow removal should be considered during heavy snow winters. Themethod of snow removal is very important, as the sequence aims to prevent unbalanced loadingconditions on the roof. Due to the risks, a properly qualified contractor should be used to remove roofsnow.

Information on snow removal can be found in Clause 6.



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A.7 ConclusionSnow storms and winter weather conditions create unique loads on buildings. Roof failures can causemillions of dollars in damages and operations interruptions. It is important for a building or facilityowner to understand the building and know its limitations prior to a snow event. A plan for action andbuilding monitoring during and after a snow event should be in place.



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Annex B (informative)Buildings at greatest risk of snow overload roof collapseNote: This Annex is not a mandatory part of this Standard.

B.1 Risk factorsThe following factors will contribute to a greater risk of snow overload roof collapse for some buildingscompared to other similar age buildings in a community:a) Location of the building and its exposure to wind (greater exposure to wind usually reduces the

amount of snow on the roof unless objects or the shape of the roof prevents the snow fromblowing off the roof);

b) The age of the building can be a significant factor in the snow load risk, especially whenmaintenance has been deficient. For example, older roof coverings might have deteriorated,sealants can shrink, and water leaking can occur. A lack of correct design or use of older codes thatmight have required lower loads than current building codes can further increase risks of roofcollapse;

c) Although a collapse can occur on any roof surface, flat roofs are more susceptible to snow and iceaccumulation and ice blockages;

d) Roof overhangs that project several metres beyond the horizontal support;e) Buildings with extensions or modification to roofs and where the construction did not consider the

original design load (e.g., installation of a new roof using original structural framework, addition ofequipment to the roof, or additional weight hanging from the roof supports);

f) A new taller structure built next to an existing building. Snow can drift from the taller building tothe lower building, which would not have been designed for the higher loads.

g) Buildings with lightweight roofs such as profile steel, asbestos, or cement sheeting can bevulnerable due to their limited inherent strength;

h) Roofs which have had their insulation properties improved can allow snow to accumulate forlonger periods without melting (from leakage of heat to roof);

i) Large span roofs;j) Low sloped or flat roofs;k) Corroded older structural steel framed roofs;l) Buildings with parapets and valleys where substantial snow drifts can accumulate;m) Staggered roof lines of differing levels that can result in snow building up on the lower roofs from

drifting or sliding snow that is deposited downwards from adjacent roofs of higher levels;n) Poor maintenance of roof drainage systems; ando) Often, commercial and industrial buildings are more susceptible to roof failure, damage and

collapse from a lack of snow and ice removal during heavy snow winters than are residentialbuildings.

Examples of risk factors can be found in Figure B.1.



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Figure B.1Illustrations of warning signs of potential and imminent roof collapse

(See Clause B.1.)

B.2 Causes of roof collapseRoof collapses due to snow overload or excessive weight of snow can happen for a number of reasonsincludinga) snow load that exceeds the building code design load for the roof;b) inadequate structural design;c) an imbalance of snow load on a roof due to drifting of snow and other factors;d) excessively wet snow or rain-soaked snow;e) failure of a key member causing others to fail as a result of load transfer;f) inadequate or blocked roof drainage systems that allow rain on snow to accumulate on the roof or

ice to form;g) added weight to roofs, such as fixed machinery or equipment, that can reduce the original load

tolerances available for snow loads and lead to collapse well below the original snow loadspecifications;

h) poor workmanship and construction detail;i) critical bracing not installed or poorly installed;j) trusses, rafters, etc. installed at wider spacing than specified in originally approved designs;k) materials of reduced quality or of smaller dimensions than specified in originally approved designs;

andl) roof deterioration due to rot, deterioration of fasteners, or cyclical racking of the roof structure.



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Annex C (informative)Snow accumulation measurementsNote: This Annex is not a mandatory part of this Standard.

C.1 GeneralThe accumulation of old and new snow on the ground is known as the snowpack. Buildings are sensitiveto the high extremes of the snowpack, whether an anomalously high depth of snow accumulation or ananomalously heavy dense snow accumulation.

Because snow is subject to drifting, melting, and natural compaction, it can be difficult to measure thedepth of the snowpack or its water equivalent and density. Any point measurement can be quitedifferent from a reading taken only a few metres away unless caution and consistency are followed intaking measurements. To better ensure consistency, monitoring procedures have been developed formeasuring snow so that readings can be compared from one location to another in any given year andfrom winter to winter at any given location. These snow measurements can be taken manually, which isthe focus of this Annex, or using automated sensors and reporting systems (i.e., data loggers). Whetherthe snow measurements are taken manually or through automated systems, the measurements shouldbe taken consistently at the same location(s) in a community from one year to another.

Snow measurements of any type should be taken about 3–4 metres from a building, fence or otherobstruction. The use of a marker driven into the ground will ensure that a consistent location formeasuring is used each year and each measurement date.

While snow depths are easier to measure, it is the snow water equivalent, or snow density,measurements that are most helpful in indicating the severity of a snow overloading condition. Sincesnow overloading conditions can develop suddenly, it is recommended that communities engage in localmonitoring of the depth and density of the snow on a regular basis.Note: Annex F provides more details on the value of these snow measurements.

C.2 Manual snow depth measurementA simplified procedure for snow depth measurement can be found in Figure C.1.Note: Manufactured snow depth measurement devices will typically come with instructions. The generalinstructions in Figure C.1 do not replace manufacturer’s instructions.

C.3 Manual snow water equivalent measurementsAn ideal snow survey site would typically be located in a relatively sheltered area but with as littleobstruction overhead as possible (e.g., tall buildings, tree canopy) and away from the influence ofdrifting around specific buildings. At each sampling period, measurements are made at several points atthe site, with the "reading" for that site being the average snow depth and water equivalent of thepoints measured.

The snow weight of accumulated snow on the ground (new and old snow) can be measured usingseveral methods. The standard method of measuring snow weight or snow water equivalent is to use a“standard snow sampler” or graduated aluminum, tube with a cutter bit affixed to the first section ofthe tubing. The tubes are driven through the snow to the ground using the cutting edge and thencarefully withdrawn, extracting a core of snow. The tube and core are then weighed using a scalespecially calibrated. The difference between the empty weight of the tubes subtracted from the weight



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of the tube and snow core is the snow water equivalent. The tubes also have graduated scales on theside which will also allow measurement of the snow depth.

At least five core measurements (up to ten measurements) should be taken for each sampling period.The maximum snow reading at most communities occurs near the beginning of April, so it is importantto take the greatest number of measurements at this time. One option to simplify measurements is toempty each snow core sample from the snow tube into a common bucket and then the total of all ofthe emptied snow cores is weighed at the end of the sampling and divided by the number of samples toobtain the average snow water equivalent measurement.

A simplified procedure for snow water equivalent measurement can be found in Figure C.2.Note: Manufactured snow depth measurement devices will typically come with instructions. The generalinstructions in Figure C.2 do not replace manufacturer’s instructions.

Figure C.1Snow depth measurement (also called “snow on the ground” measurement)

(See Clause C.2.)

��

1 2 3

Notes:1) The depth of snow on the ground includes both new snow and old snow which was in place. Find a location

for snow depth measurements where the snow appears to be near its average depth, avoiding drifts orvalleys.

2) Measure the depth with a snow measuring stick (aka “ruler”) or using the depth indicator on a snowsampling tube. Insert the measurement stick exactly vertically into the snow until the ground is reached.

3) Record the snow depth at the top of the snowpack. Measure at several locations and use an average of themeasurements.



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Figure C.2Snow water equivalent measurement

(See Clause C.3.)

��

��

��

��

��

1020304050

1 2 3

4 5 6

Notes:1) Clean the snow tube of debris, snow, etc.2) Weigh the snow tube.3) Insert tube exactly vertically; rotate tube into the snowpack to reach the ground.4) Twist sharply when the tube has reached the ground (be careful not to get too much soil in the snow sample).5) Pull out vertically.6) When an entire column has been removed, weigh the tube and snow core (exercise caution so that the snow

sample does not fall out of the tube). Subtract the total weight from the weight of the tube. At least 5 snowcores should be sampled and measured (up to 10). Sometimes, all of the cores can be emptied into a common



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bucket and the weight of all of the samples averaged (i.e., total weight of the snow samples divided by thenumber of samples).



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Annex D (informative)Building access markingsNote: This Annex is not a mandatory part of this Standard.

D.1 MarkingsAfter classifying a building for snow overload risks in accordance with Clause 5.6, a safety classificationof each building, including all possible hazards, should be identified by posting a coloured marking oneach inspected building as close as possible to all entryways. Markings should correspond to one of thethree access categories specified in Clauses D.2 to D.4. The meaning of each marking should beexplained to users and occupants.

This Annex has been developed to provide guidance on development of a system of markings wherenone exist.

D.2 Red marking: “ACCESS PROHIBITED”

D.2.1A red marking (see Figure D.1) marked “ACCESS PROHIBITED” prohibits access to the building, and is tobe used when building safety and structural integrity are severely compromised and pose a threat tothe safety and security of the public.Notes:1) It is important to note that an “Access Prohibited” classification does not correspond to an order of

demolition. It is a precaution intended to prevent people from endangering their safety in case of potentiallylethal hazards. After the emergency is dealt with, the building owner, manager, or competent individual of thebuilding can seek advice from an engineering consulting office on the best course of action to follow.

2) The French equivalent of “Access Prohibited” is “Accès Interdit”.

D.2.2Access to the building or cordoned-off area should be restricted to authorized personnel only.

D.2.3Upon completion of the evaluation, the building owner, manager, or competent individual of thebuilding may appoint a structural engineer to further assess the state of the building. Based on thefurther evaluation, a decision could be made to demolish the damaged building or to restore it to a safeand fully functional state.

D.3 Amber marking: “LIMITED ACCESS”

D.3.1An amber marking (see Figure D.2) marked “LIMITED ACCESS” indicates conditional access. This markingshould be affixed to buildings whose level of safety is uncertain with entry by the public prohibited.Note: The French equivalent of “Limited Access” is “Accès Limité”.



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D.3.2Entry by rescue personnel should be permitted for emergencies only. Explanatory remarks outliningsuch conditions should be indicated on the marking. Entry by the building owner, manager, orcompetent individual may be permitted upon special approval.Note: Building owner, manager, or competent individual access may be granted only by those with authorization todo so.

D.3.3When a building receives an amber or red marking, precautions should be taken to maintain the safetyof adjacent structures.Note: Ensuring the safety of adjacent structures can be accomplished by evacuating buildings in the immediatevicinity of the damaged area and by shutting down their services (e.g., gas, electricity, etc.).

D.4 Green marking: “UNRESTRICTED ACCESS”A green marking (see Figure D.3) marked “UNRESTRICTED ACCESS” indicates full access with norestrictions on building entry and use. Buildings receiving a green marking meet the minimumrequirements for safe use and occupancy.

In the event that a potentially unsafe condition has been overlooked by the inspecting team, users andoccupants should be advised to immediately report suspected hazards to local authorities for furtherevaluation.Note: The French equivalent of “Unrestricted Access” is “Un Accès Illimité”.

D.5 Building markings

D.5.1 Preliminary evaluation stage

D.5.1.1In the case of “Safety Uncertain” or “Unsafe” conditions, the marking of a building or vicinity should beaccomplished by affixing safety classification markings to the following:a) entrances;b) passageways; andc) all other access points to any danger zones.

D.5.1.2In the case of “Safe” conditions, no marking is required. A green “Unrestricted Access” marking may beaffixed to notify that the building is safe to enter.

D.5.2 Structural evaluation stage

D.5.2.1Similar to the preliminary evaluation stage, the safety classification of a building, including all possiblehazards, should be identified by posting a coloured marking on each entry gate or access door to thebuilding inspected. Markings should correspond to one of the three access categories specified inClauses D.2 to D.4.

D.5.2.2In case of an amber marking, the building should be scheduled for a structural evaluation.



in Canada’s North


Figure D.1Example: Marking of “clearly unsafe” conditions

(See Clause D.2.1.)

Inspected site name and address Date

Time

This building was inspected underthe following jurisdiction

Inspector

ID:

Affiliation:

Comments:This building’s safety has beenseverely compromised and poses a serious threat to life ofusers and occupants. Do notenter. Trespassing may resultin injury or death.

Previous posting:

by

DANGER AREA — DO NOT ENTERRemoval of this placard must be approved by Authority having jurisdiction



in Canada’s North


Figure D.2Example: Marking of “safety uncertain” conditions

(See Clause D.3.1.)


Time


Inspector

ID:

Affiliation:

Restrictions on access

Emergency purposes only

Other

This building has beendamaged and does not meetminimum requirements forsafe use and occupancy.Violation of the posted restrictions may result ininjury or death.

Previous posting:

by

RESTRICTED AREA — AUTHORIZED ENTRY ONLYRemoval of this placard must be approved by Authority having jurisdiction



in Canada’s North


Figure D.3Example: Marking of “safe” conditions

(See Clause D.4.)


Time


Inspector

ID:

Affiliation:

This inspection was performed

OUTSIDE

OUTSIDE and INSIDE

This building has beeninspected and meets minimumrequirements for safe use and occupancy. Any potentiallyunsafe condition should bereported to local authoritiesfor further evaluation

Previous posting:

by

NO RESTRICTIONS ON USE OR OCCUPANCYRemoval of this placard must be approved by Authority having jurisdiction



in Canada’s North


Annex E (informative)Assessment formNote: This Annex is not a mandatory part of this Standard.

E.1 Accumulated snowfall roof assessment formTable E.1 provides a sample form used for the assessment of a roof that has been subjected to heavysnowfall.

This assessment form should be developed as part of the snow removal plan in Clause 4.2.3 and used inaccordance with Clause 5.4.3.

E.2 Historical snow load dataIn order to properly assess the impact and risk of accumulated snow on a roof, it is important to assessthe original capacity of the roof.

Tables E.2 and E.3 provide historical snow loads for Northwest Territories, Nunavut, and the Yukondating back to 1961. A comparison between the snow loads of the original year of construction andcurrent snow measurements will provide guidance of determination of risk.



in Canada’s North


Table E.1Sample assessment form

(See Clause E.1.)



in Canada’s North




in Canada’s North


TableE.2

Historicalsnowload

data(Metric)

(SeeClauseE.2.)

Yukon

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long.

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Aishihik

YT92

061

.60

-137

.52

1.9

0.1

1.9

0.1

1.9

0.1

1.8

0.1

1.8

0.1

1.3

1.3

1.3

1.2

1.2

1.2

1.2

Dawson

YT33

064

.07

-139

.42

2.9

0.1

2.7

0.1

2.7

0.1

2.5

0.1

1.9

0.1

2.6

2.6

2.6

2.8

2.8

2.8

2.8

2.8

DestructionBa

yYT

815

61.25

-138

.80

1.9

0.1

1.6

0.1

1.6

0.1

1.5

0.1

2.0

0.1

2.6

2.6

2.6

2.4

2.4

Faro

YT67

062

.23

-133

.36

2.3

0.1

2.3

0.1

Haines

Junctio

nYT

600

60.78

-137

.54

2.2

0.1

2.2

0.1

Snag

YT59

562

.40

-140

.37

2.2

0.1

2.2

0.1

2.2

0.1

2.0

0.1

2.0

0.1

2.4

2.4

2.4

2.4

2.4

2.4

2.4

Teslin

YT69

060

.17

-132

.72

3.0

0.1

2.9

0.1

2.9

0.1

2.7

0.1

1.7

0.1

2.2

2.2

2.2

1.6

1.6

1.6

1.6

WatsonLake

YT68

560

.13

-128

.71

3.2

0.1

3.1

0.1

3.1

0.1

2.9

0.1

2.2

0.1

2.7

2.7

2.7

2.6

2.6

2.6

2.6

Whiteho

rse

YT65

560

.72

-135

.05

2.0

0.1

1.8

0.1

1.8

0.1

1.7

0.1

1.7

0.1

1.7

1.7

1.7

1.7

1.3

1.3

1.3

1.3

NorthwestTerritories

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat

Long

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Aklavik

NT

568

.23

-135

.01

2.8

0.1

2.3

0.1

2.3

0.1

2.1

0.1

2.1

0.1

2.2

2.2

2.2

2.2

2.2

2.2

2.2

Echo

Bay/Po

rtRa

dium

NT

195

66.05

-117

.88

3.0

0.1

3.0

0.1

30.1

2.8

0.1

2.8

0.1

2.7

2.7

2.7

2.6

2.6

2.6

2.6

FortGo

odHo

peNT

100

66.29

-128

.63

2.9

0.1

2.9

0.1

2.9

0.1

2.7

0.1

2.7

0.1

2.8

2.8

2.8

2.9

2.9

2.9

2.9

FortMcPhe

rson

NT

2567

.43

-134

.88

3.2

0.1

2.3

0.1

FortProv

iden

ceNT

150

61.35

-117

.65

2.4

0.1

2.4

0.1

2.4

0.1

2.2

0.1

2.2

0.1

2.5

2.5

2.5

2.3

2.3

2.3

2.3

FortRe

solutio

nNT

160

61.19

-113

.67

2.3

0.1

2.3

0.1

2.3

0.1

2.1

0.1

2.1

0.1

2.3

2.3

2.3

2.2

2.2

2.2

2.2

FortSimpson

NT

120

61.93

-121

.35

2.3

0.1

2.3

0.1

2.3

0.1

2.1

0.1

2.1

0.1

2.5

2.5

2.5

2.7

2.7

2.7

2.7

FortSm

ithNT

205

60.00

-111

.88

2.3

0.2

2.3

0.2

2.3

0.2

2.1

0.2

2.1

0.2

2.0

2.0

2.0

1.8

1.8

1.8

1.8

HayRiver

NT

4560

.85

-115

.73

2.4

0.1

2.4

0.1

2.4

0.1

2.2

0.1

2.2

0.1

2.6

2.6

2.6

2.4

2.4

2.4

2.4

2.4

Inuv

ikNT

4568

.35

-133

.72

3.1

0.1

2.3

0.1

2.3

0.1

2.1

0.1

2.1

0.1

2.2

2.2

2.2

2.2

2.2

2.2

2.2

2.2

(Continued)



in Canada’s North


TableE.2(Continued)


50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat

Long

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Mou

ldBa

yNT

576

.23

-119

.33

1.5

0.1

1.5

0.1

1.5

0.1

1.4

0.1

1.4

0.1

1.0

1.0

1.0

1.1

1.1

1.1

1.1

Norman

Wells

NT

6565

.28

-126

.85

3.0

0.1

2.7

0.1

2.7

0.1

2.5

0.1

2.5

0.1

3.3

3.3

3.3

3.0

3.0

3.0

3.0

3.0

Rae-Ed

zoNT

160

62.83

-116

.05

2.3

0.1

2.3

0.1

2.3

0.1

2.1

0.1

2.1

0.1

2.4

2.4

2.4

2.3

2.3

2.3

2.3

Tung

sten

NT

1340

61.95

-128

.27

4.3

0.1

4.3

0.1

4.3

0.1

4.0

0.1

6.6

0.1

3.0

3.0

3.0

2.9

Ulukh

aqtuuq

/Ho

lman

NT

1070

.73

-117

.75

2.1

0.1

2.1

0.1

2.1

0.1

1.9

0.1

1.9

0.1

1.4

1.4

1.4

1.2

1.2

1.2

1.2

Wrig

ley

NT

8063

.23

-123

.47

2.8

0.1

2.8

0.1

Yello

wkn

ifeNT

160

62.48

-114

.35

2.2

0.1

2.2

0.1

2.2

0.1

2.0

0.1

2.0

0.1

2.0

2.0

2.0

42.0

42.0

42.0

42.0

42.0

Nunavut

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Alert

NU

582

.48

-62.25

2.6

0.1

1.6

0.1

1.6

0.1

1.5

0.1

1.5

0.1

1.9

1.9

1.9

2.1

2.1

2.1

2.1

ArcticBa

yNU

1573

.03

-85.17

2.4

0.1

2.1

0.1

2.1

0.1

1.9

0.1

1.9

0.1

1.4

1.4

1.4

0.9

0.9

0.9

0.9

Arviat/Eskim

oPo

int

NU

561

.12

-94.05

3.0

0.2

2.9

0.2

2.9

0.2

2.7

0.2

2.7

0.2

2.7

2.7

2.7

2.7

2.7

2.7

2.7

BakerL

ake

NU

564

.32

-96.02

3.4

0.2

2.9

0.2

2.9

0.2

2.7

0.2

2.7

0.2

2.0

2.0

2.0

1.5

1.5

1.5

1.5

Eureka

NU

579

.98

-85.95

1.6

0.1

1.6

0.1

1.6

0.1

1.5

0.1

1.5

0.1

1.0

1.0

1.0

1.2

1.2

1.2

1.2

Igluligaarju

k/Ch

esterfield

Inlet

NU

1063

.33

-90.70

3.6

0.2

3.0

0.2

30.2

2.8

0.2

2.8

0.2

2.6

2.6

2.6

2.4

2.4

2.4

2.4

Iqaluit/Frob

isher

Bay

NU

4563

.73

-68.50

2.9

0.2

2.9

0.2

2.9

0.2

2.7

0.2

2.7

0.2

2.2

2.2

2.2

2.4

2.4

2.4

2.4

2.4

Iqaluk

tuuttia

q/Ca

mbridge

Bay

NU

1569

.12

-105

.03

1.9

0.1

1.6

0.1

1.6

0.1

1.5

0.1

1.5

0.1

1.4

1.4

1.4

1.5

1.5

1.5

1.5

Isachsen

NU

1078

.78

-103

.53

1.9

0.1

1.6

0.1

1.6

0.1

1.5

0.1

1.5

0.1

1.3

1.3

1.3

1.4

1.4

1.4

1.4

Kang

iqiniq/Ran

kin

Inlet

NU

1062

.82

-92.08

3.0

0.2

3.0

0.2

30.2

2.8

0.2

2.8

0.2

2.6

2.6

2.6

2.5

2.5

2.5

2.5

Kann

giqtug

aapik/

Clyd

eRiver

NU

570

.45

-68.57

4.2

0.2

3.5

0.2

3.5

0.2

3.2

0.2

3.2

0.2

2.5

2.5

2.5

2.6

2.6

2.6

2.6

(Continued)



in Canada’s North


TableE.2(Concluded)

Nunavut

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Kugluk

tuk/

Copp

ermine

NU

1067

.83

-115

.08

3.4

0.1

2.6

0.1

2.6

0.1

2.4

0.1

2.4

0.1

1.9

1.9

1.9

2.2

2.2

2.2

2.2

Nottin

gham

Island

NU

3063

.10

-78.00

4.7

0.2

4.5

0.2

4.5

0.2

4.2

0.2

4.2

0.2

3.4

3.4

3.4

4.1

4.1

4.1

4.1

Resolute

NU

2574

.68

-94.90

2.0

0.1

1.7

0.1

1.7

0.1

1.6

0.1

1.6

0.1

1.3

1.3

1.3

1.3

1.3

1.3

1.3

1.3

Resolutio

nIsland

NU

561

.30

-64.88

5.5

0.2

5.2

0.2

5.2

0.2

4.8

0.2

4.8

0.2

4.6

4.6

4.6

5.6

5.6

5.6

5.6

Salliq/Co

ral

Harbou

rNU

1564

.13

-83.17

3.8

0.2

3.8

0.2

3.8

0.2

3.5

0.2

3.5

0.2

3.1

3.1

3.1

2.9

2.9

2.9

2.9

Note:

Data

courtesy

ofEn

vironm

entC

anad

aan

dtheNationa

lResea

rchCo

uncilo

fCan

ada.

SL=Snow

load

(198

5an

dea

rlier)

SLr=Snow

load

dueto

rain

falling

into

snow

ontheroof

SLs=Snow

load

dueto

accumulated

snow

(buildingcode

sconvertg

roun

dsnow

toroof

load

s)



in Canada’s North


TableE.3

Historicalsnowload

data(Imperial)

(SeeClauseE.2.)

Yukon

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long.

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Aishihik

YT92

061

.60

-137

.52

402

402

402

382

382

2727

2726

2626

26

Dawson

YT33

064

.07

-139

.42

612

562

562

522

402

5454

5458

5858

5858

DestructionBa

yYT

815

61.25

-138

.80

402

332

332

312

422

5454

5450

50

Faro

YT67

062

.23

-133

.36

482

482

Haines

Junctio

nYT

600

60.78

-137

.54

462

462

Snag

YT59

562

.40

-140

.37

462

462

462

422

422

5050

5050

5050

50

Teslin

YT69

060

.17

-132

.72

632

612

612

562

362

4646

4634

3434

34

WatsonLake

YT68

560

.13

-128

.71

672

652

652

612

462

5656

5654

5454

54

Whiteho

rse

YT65

560

.72

-135

.05

422

382

382

362

362

3636

3635

2727

2727


50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long.

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Aklavik

NT

568

.23

-135

.01

582

482

482

442

442

4646

4646

4646

46

Echo

Bay/Po

rtRa

dium

NT

195

66.05

-117

.88

632

632

632

582

582

5656

5654

5454

54

FortGo

odHo

peNT

100

66.29

-128

.63

612

612

612

562

562

5858

5860

6060

60

FortMcPhe

rson

NT

2567

.43

-134

.88

672

482

FortProv

iden

ceNT

150

61.35

-117

.65

502

502

502

462

462

5252

5248

4848

48

FortRe

solutio

nNT

160

61.19

-113

.67

482

482

482

442

442

4848

4845

4545

45

FortSimpson

NT

120

61.93

-121

.35

482

482

482

442

442

5252

5256

5656

56

FortSm

ithNT

205

60.00

-111

.88

484

484

484

444

444

4242

4237

3737

37

HayRiver

NT

4560

.85

-115

.73

502

502

502

462

462

5454

5450

5050

5050

Inuv

ikNT

4568

.35

-133

.72

652

482

482

442

442

4646

4646

4646

4646

(Continued)



in Canada’s North


TableE.3(Continued)


50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long.

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Mou

ldBa

yNT

576

.23

-119

.33

312

312

312

292

292

2121

2122

2222

22

Norman

Wells

NT

6565

.28

-126

.85

632

562

562

522

522

6969

6963

6363

6363

Rae-Ed

zoNT

160

62.83

-116

.05

482

482

482

442

442

5050

5048

4848

48

Tung

sten

NT

1340

61.95

-128

.27

902

902

902

842

138

263

6363

60

Ulukh

aqtuuq

/Ho

lman

NT

1070

.73

-117

.75

442

442

442

402

402

2929

2925

2525

25

Wrig

ley

NT

8063

.23

-123

.47

582

582

Yello

wkn

ifeNT

160

62.48

-114

.35

462

462

462

422

422

4242

4242

4242

4242

Nunavut

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long.

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Alert

NU

582

.48

-62.25

542

332

332

312

312

4040

4043

4343

43

ArcticBa

yNU

1573

.03

-85.17

502

442

442

402

402

2929

2919

1919

19

Arviat/Eskim

oPo

int

NU

561

.12

-94.05

634

614

614

564

564

5656

5656

5656

56

BakerL

ake

NU

564

.32

-96.02

714

614

614

564

564

4242

4232

3232

32

Eureka

NU

579

.98

-85.95

332

332

332

312

312

2121

2125

2525

25

Igluligaarju

k/Ch

esterfield

Inlet

NU

1063

.33

-90.70

754

634

634

584

584

5454

5450

5050

50

Iqaluit/Frob

isher

Bay

NU

4563

.73

-68.50

614

614

614

564

564

4646

4650

5050

5050

Iqaluk

tuuttia

q/Ca

mbridge

Bay

NU

1569

.12

-105

.03

402

332

332

312

312

2929

2932

3232

32

Isachsen

NU

1078

.78

-103

.53

402

332

332

312

312

2727

2730

3030

30

Kang

iqiniq/Ra

nkin

Inlet

NU

1062

.82

-92.08

634

634

634

584

584

5454

5452

5252

52

Kann

giqtug

aapik/

Clyd

eRiver

NU

570

.45

-68.57

884

734

734

674

674

5252

5254

5454

54

(Continued)



in Canada’s North


TableE.3(Concluded)

Nunavut

50-yearreturn

period

30-yearreturn

period

Location

Prov

Elev

(m)

Lat.

Long.

2015

SLs

2015

SLr

2010

SLs

2010

SLr

2005

SLs

2005

SLr

1995

SLs

1995

SLr

1990

SLs

1990

SLr

1985 SL

1980 SL

1977 SL

1975 SL

1970 SL

1968 SL

1965 SL

1961 SL

Kugluk

tuk/

Copp

ermine

NU

1067

.83

-115

.08

712

542

542

502

502

4040

4045

4545

45

Nottin

gham

Island

NU

3063

.10

-78.00

984

944

944

884

884

7171

7185

8585

85

Resolute

NU

2574

.68

-94.90

422

362

362

332

332

2727

2727

2727

2727

Resolutio

nIsland

NU

561

.30

-64.88

115

410

94

109

410

04

100

496

9696

117

117

117

117

Salliq/Co

ral

Harbou

rNU

1564

.13

-83.17

794

794

794

734

734

6565

6561

6161

61

Note:

Data

courtesy

ofEn

vironm

entC

anad

aan

dtheNationa

lResea

rchCo

uncilo

fCan

ada.

SL=Snow

load

(198

5an

dea

rlier)

SLr=Snow

load

dueto

rain

falling

into

snow

ontheroof

SLs=Snow

load

dueto

accumulated

snow

(cod

esconvertg

roun

dsnow

toroof

load

s)



in Canada’s North


Annex F (informative)Snow loads, climate change and buildings: A DiscussionNote: This Annex is not a mandatory part of this Standard.

F.1 IntroductionEngineers Canada1 and the Army Corps of Engineers (USACE)2 have recognized that adaptation orcoping with climate change involves many risk management decisions. The USACE describes mitigationmeasures (i.e., reductions of GHG emissions) as “avoiding the unmanageable impacts”, andcharacterizes adaptation to climate change as “managing the unavoidable impacts”.

Climate-informed risk management decisions must incorporate projected climate change trends anduncertainties. According to the USACE, planning for adaptation requires the use of the best availableand actionable climate science and climate change information, which should be followed with rational,legally justifiable methods, processes, and policies.

This Annex provides guidance and good practice suggestions to help with climate change riskmanagement decisions for design and construction of buildings, but does not dictate individualapproaches. Rather, the intent is to provide the information needed to support robust and defensibleengineering practices for climate change at various decision-points. This guidance is designed to beflexible enough to recognize the value of local knowledge and can also be adjusted for current state-of-the-science climate information and future climate change science developments in climate risk-informed decision-making.3

F.2 The changing climate of the NorthThe most recent climate change science tells us that changes in temperatures, rainfall, snowaccumulations, wind loads, accelerated weathering or deterioration of materials, and other severeweather events will affect the safety and reliability of buildings, housing, and communities, mostseverely in Canada’s North. The Intergovernmental Panel on Climate Change (IPCC) released its FifthAssessment (AR5) on climate science in late 20134 and concluded that it is now “unequivocal” that theearth has warmed since the start of the 20th Century5. This IPCC report, considered by governments asone of the most comprehensive, credible, and scrutinized sources on climate change, also concludedthat, since the 1950s, many of the observed changes were unprecedented over decades tomillennia4,5,6.

As is the North to the rest of Canada, so is Canada to the rest of the world: the rate of warming inCanada has been, on average, greater than the rate of the global change, with annual increases of 1.5 °C in mean temperature observed in Canada from 1950 to 20107,8, and even greater warming of up to 3 °C observed in the North over a similar period (see Figure F.1). Warming of the North and other regionsof Canada has also included changes in the frequency and intensity of precipitation, including moreintense precipitation events – as well as poleward shifts in storm tracks and changes in the number andintensity of storm systems7,8,9,10.

Analysis of precipitation data indicates that many regions in Canada have, on average, been tendingtowards wetter conditions or more precipitation. These increases have been most notable andstatistically significant in Canada’s North, as seen in Figure F.2. Trends in Canada’s North indicate that allseasons have become wetter, including winters, with snow amounts increasing in many parts of theNorth6,7. At the same time, however, the length or duration of the Northern winter snow season hasdecreased, with snow cover occurring later in the autumn and with earlier spring breakup. Increases in



in Canada’s North


precipitation extremes (for daily precipitation data) have been found to be greater than the increases inmean precipitation in many regions of Canada (including the North). This means that precipitationamounts are being more often influenced by the heavier events7,8,11. While the climate has always beenchanging throughout time, it is clear that many of these and other observed changes are beyond whatcan be explained by the natural variability of the climate.

Figure F.1 illustrates recent temperature increases observed in various regions of Canada’s North whileFigure F.2 illustrates the increasing trends in precipitation amounts in all seasons and regions.

Figure F.1Mean temperature departures from 1961 to 1990 climate normalsand linear trend for Canada and climatic regions, 1948 to 2009

(From Statistics Canada using Environment Canada’s homogenized climate data)(See Clause F.2.)

Arctic Tundra

199819881978196819581948 2008

3

2

1

0

–1

–2

–3

4°C

–4

3

2

1

0

–1

–2

–3

4°C

–4

Mackenzie District

199819881978196819581948 2008

3

2

1

0

–1

–2

–3

4°C

–4

3

2

1

0

–1

–2

–3

4°C

–4

Yukon and North British Columbia mountains

199819881978196819581948 2008

3

2

1

0

–1

–2

–3

4°C

–4

3

2

1

0

–1

–2

–3

4°C

–4

Arctic mountains and fiords

199819881978196819581948 2008

3

2

1

0

–1

–2

–3

4°C

–4

3

2

1

0

–1

–2

–3

4°C

–4

Departure from normal Linear trend



in Canada’s North


Figure F.2Linear trends associated with seasonal mean precipitation percentage departurefrom 1961 to 1990 climate normals for northern climatic regions, 1948 to 2009(From Statistics Canada using Environment Canada’s homogenized climate data)

(See Clause F.2.)Arctic mountains and fiords

199819881978196819581948 2008

20

10

0

–10

–20

–30

30%

30

20

10

0

–10

–20

–30

% Arctic tundra

199819881978196819581948 2008

20

10

0

–10

–20

–30

30%

30

20

10

0

–10

–20

–30

%

Mackenzie District

199819881978196819581948 2008

20

10

0

–10

–20

–30

30%

30

20

10

0

–10

–20

–30

% Yukon and North British Columbia

199819881978196819581948 2008

20

10

0

–10

–20

–30

30%

30

20

10

0

–10

–20

–30

%

Spring Summer Fall Winter

F.3 Future climate changeProjections of the future climate are typically based on a number of climate change scenario models,with each model based on certain assumptions of future GHG concentration trends and feed-backloops. While of course no one can foretell the future, each of the past five IPCC assessments hasconsistently, and with increased confidence, concluded that there is a direct correlation betweenhuman-generated greenhouse gases (GHG) and changes to the earth’s climatic patterns. The mostrecent IPCC Fifth Assessment Report (AR5)4 states, “It is extremely likely that human influence has beenthe dominant cause of the observed warming since the mid-20th century. Continued emissions ofgreenhouse gases will cause further warming and changes in all components of the climate system,likely at greater rates than that observed during the past century.” Indeed, the 2013 IPCC report statesthat efforts to limit future climate change will require “substantial and sustained reductions ofgreenhouse gas emissions”4.

The IPCC projects temperature increases exceeding the critical 2 °C globally before the year 2100, withthe greatest warming expected under the higher GHG emission assumptions4. The GHG emissionassumptions used in the AR5 assessment are called “representative concentration pathways” (RCPs)12.Scientific evidence indicates that some of the greatest temperature increases globally can be expectedin Canada’s high Arctic regions, with the warming exceeding 7–9 °C by the end of this century under themore aggressive GHG emission assumptions4.



in Canada’s North


Along with the increase in temperatures, the climate models indicate increases in precipitation forCanada’s North, consistent with trends already being experienced7, 8, 10, 11. Since the capacity of theatmosphere to hold moisture (water vapor) increases with temperature, Arctic regions can expect moreextreme snowfalls during months when temperatures remain below freezing. Recent observed trendsindicate that the proportion of precipitation falling as snow has generally increased, as have trends inone-day snowfall7, 8. The Vincent and Mekis studies also indicate that the number of days in Arcticregions with heavy snowfall have also shown increases that are statistically significant7,8. Fortemperatures above 10 °C, the scientific studies indicate that extreme short duration rainfall events (e.g., heavy one day rainfall) also could increase significantly (by as much as 14%), highlighting significantimplications for community drainage risks and permafrost thawing13, 14.

Recent snowload roof collapses in the North and in other parts of Canada demonstrate the increasedrisk of changing snowfall extremes, seasonal accumulations of snow, rain on snow conditions, andsnowpack densities. In many of the forensic studies of snow overload roof collapses in the NWT, there isa good probability that the ground snow loads at the times of failure exceeded the NBCC recommendedclimatic design values at some locations15. These findings highlight the importance of monitoring trendsin snow conditions, along with an urgent need for building codes to be regularly updated with the morerecent snow load values. In addition, changing snow extremes indicate that additional safety factorsmay need to be considered in designs for Northern buildings. The findings also highlight an urgent needfor a more critical examination of the snow density assumptions currently incorporated into designground snow load calculations.

Studies of the major snow storm events in the United States11, 16 (where, with the exception of Alaska,winters are typically warmer than in Canada’s North) indicate that historically, severe snowstorms oftenoccur during warmer than normal winters in regions where winter temperatures are typically near orbelow freezing. The Changnon et al (2006) study for U.S. snow extremes11 found that 61% to 85% of allsevere snow storms occurred in wetter-than-normal winters, or winters with wetter or heavier thannormal precipitation. These findings are backed by other studies indicating that, while the winter snowseason will likely shorten, large snow storms might become bigger and more intense in a future withwetter and warmer winters. In Canada’s North, these studies point to more severe snowstorms andpotentially, heavier snow loads.

Figure F.3 illustrates some typical outputs from an ensemble of 40 climate change model projectionsusing the most recent 2012 IPCC Fifth Assessment Report (AR5) results. The outputs are applicable for aregion near the southern boundary of the Yukon and Northwest Territories, and for a period fromMarch to May. The ensemble results are shown for two different future GHG assumptions: the globallyreduced GHG assumption RCP4.5 that posits significant reductions in emissions into the future, and thehighest GHG assumption RCP8.5, which closely approximates real observed trends on releases of GHGsinto the atmosphere.



in Canada’s North


Figure F.3Examples of adjusted climate change model results

(Courtesy of Risk Sciences International and based on IPCC (2013) results)(See Clause F.3.)

170

160

150

140

130

180

120

3

2

1

0

–1

4

–2

20

15

10

5

0

25

2050s2020s1981-2010 2080s 2050s2020s1981-2010 2080s

2050s2020s 2080s

20

15

10

5

0

25

30

2050s2020s 2080s

RCP4.5

RCP8.5

RCP8.5RCP4.5

RCP8.5

RCP4.5

RCP8.5

61.46N, 128.27W AR5Ensemble spring precipitation (mm)

SE Yukon AR5 ensemble annualchange in precipitation (%)from 1981-2010 baseline

SE Yukon AR5 ensemble 1 day meanmax precipitation change (%)

from 1981-2010

61.46N, 128.27W AR5Ensemble spring Tmax (°C)

Notes:1) Taken for a location in southeastern Yukon and near the border with the NWT. The results represent outputs

from an “ensemble” of 40 climate change models released for the IPCC AR5 assessment reports (2013-14).The charts were developed by Risk Sciences International in support of the Climate and InfrastructureForensics Analyses System (CIFAS).

2) Top charts: IPCC AR5 ensemble projections of spring-late winter precipitation (left) and maximumtemperatures (right) for grid cells near the southern Yukon and NWT borders.

3) Bottom Charts: IPCC AR5 ensemble projections of % changes to annual precipitation compared to 1981-2010interpolated values for grid cell near southern Yukon-NWT border (left) and % changes to one day maximumprecipitation compared to 1981–2010 interpolated values. All climate change outputs have been initiallycalibrated or ground-truthed for the current climate.

F.4 Buildings at riskStudies by the Government of the Northwest Territories (GNWT) indicate that approximately 22% of thepublic access buildings in the NWT — schools, hospitals and medical facilities, community centers—havebeen found to be at some risk of collapse from increasing snow loads17. Some of these buildings havebeen retrofitted, while others (approximately 12%) were designated under snow overload "watch"status17. As a result, many buildings designed for the NWT Government use higher ground snow loadvalues than required in subsequent versions of the National Building Code of Canada. The use of a



in Canada’s North


factor to augment the ground snow load values could be considered equivalent to application ofincreased safety margins or a “climate change adaptation factor”18,19. The use of a climate changeadaptation safety factor provides resilience needed under current climate conditions, and supportsmore resilience under a range of future climate change projections. According to the IPCC SpecialReport on Extremes5,such “no regrets” to “low regrets” measures provide good starting points foraddressing ongoing and future trends in vulnerability to climate extremes, and have the potential tooffer benefits now and to lay the foundation for addressing projected future changes20.

The majority of public buildings that were identified as being in danger of collapse by the Governmentof NWT were relatively recently built, designed under fairly recent building codes and utilized the latestavailable ground snow load data published in the NBCC. In spite of the snow live-load factors inherent inour current limit states design approach, some of these recent buildings have still been failing or beenassessed as “at snow overload risk”. This raises the concern: If buildings have failed, are not others,designed by the same set of methodologies, also in danger of collapse under increasing snow loads thatexceed design conditions? How can designers and builders reduce these risks?

F.5 Managing the risksBearing in mind that building codes generally establish minimum levels of design, the NBCC providestwo different approaches to the design of buildings, according to their use and size.

These different approaches to design relate directly to those considered as “competent individuals” inthe context of this Standard:

1. Small buildings that have stood the test of time: For houses and small buildings, Part 921 of the NBCCprovides prescriptive design clauses and sizing tables that are based on decades of observation of theperformance of these types of standard structures as they have been subjected to the “environmentalloads” of wind, snow, and rain typical of the various regions of local climates (as well as seismic activityin different geological locations). Note that anyone may design houses and small buildings “under Part9”, provided the methodology therein is followed. For example, Part 9 contains rafter span tables,showing maximum allowable spans, depending on the rafter depth and the wood species and gradeused. If a span is longer than what is shown in the tables, a professional structural engineer must beengaged to design a roof system capable of supporting the design loads. However, as long as theprescriptive approach contained in Part 9 is followed, a structural engineer is not required. For thepurposes of this Standard, a competent individual for the types of small buildings covered in Part 9 isanyone who has a firm demonstrable understanding of this Part of the NBCC. Such competentindividuals might be skilled carpenters, building inspectors, architects, building technicians, and so forth.

2. Larger buildings: For buildings larger than those dealt with in Part 9, and for buildings used for morepublic institutional occupancy (categorized as “Groups A or B” in the NBCC), or for high hazard industrialstructures — in other words all buildings (or components thereof) that do not fall under the umbrella of“Part 9 buildings” — only professional structural engineers are permitted to provide structural designs.Having a heretofore reasonable expectation that the past will be the key to the future, structuralengineers rely on historical wind, snow, rain, and earthquake loads that are found in the NBCC tocalculate these environmental loads their building will likely encounter during its lifetime. Standardmethodologies and mathematical expressions for determining them are provided in Part 4 of the NBCC— augmented in greater depth in Part 4 Commentary. With these anticipated environmental loadsunderstood, cZlimit states design expressions for a standard building material’s22 resistance to loads areused to ensure that factored strength exceeds factored load. Incidentally, Part 3 of the NBCC deals withFire Protection, Occupant Safety, and Accessibility according to types of building occupancy. Only



in Canada’s North


professional structural engineers are considered to be competent individuals for the types of buildingsdealt with in Part 4.

As our climate continues to change, it is becoming clear that the historical climatic design data in theNBCC will become less and less representative of the future climate and that many future climate riskswill be significantly under-estimated17,18,19. It cannot be assumed that the future will be similar to thepast, and probabilities estimated from trends in the historical data cannot be simply projected into thefuture1,2,5,17,18,19,23.. The IPCC concluded in their 2012 Special Report on Extremes5 that “Based on arange of emissions scenarios,…a 1-in-20 year annual maximum daily precipitation amount is likely tobecome a 1-in-5 to 1-in-15 year event by the end of the 21st century in many regions, and in mostregions the higher emissions scenarios…lead to a stronger projected decrease in return period”.

Figure F.4 conceptually illustrates that impact of increasing extremes on return period values of climateextremes. Future increases in precipitation extremes effectively reduce the return periods associatedwith the climatic design values. For example, a current 50-year return period value used in codes orstandards could effectively represent a 25-year or lower return period amount near the end of thiscentury. The magnitude of a 50-year return period extreme event will be significantly higher near theend of the century, with the impact that the magnitude of the current 50-year return period couldrepresent less than a 25-year return period value before the end of this century.

Figure F.4Projected changes in extreme 24-hour precipitation amounts and return periods

(See Clause F.5.)

10 20 40 60 80 100

2090

1990

CGCM.1/T63SRES A2

205580

70

60

90

90

Event recurrence time (years)

Size

of e

vent

(mm

)

Projected changes in extreme 24-hr precipitation eventsNorth America (25N-65N)

Notes:1) Future (green and red contours) for North America compared to 1990 values (blue contour).2) Results are based on outputs from the 2007 Canadian climate change model (CGCM3.1) using one higher

GHG emission assumption (IPCC AR4). (Figure from F.W. Zwiers and S. Slava, based on paper by Kharin et al.,2007.)

3) The Canadian CGCM3 (A2) North American projections depicted in this Figure are similar to results from otherensembles of North American climate change projections. All of the models used in the multi-model ensembleprojected an increase in North American extreme 24-hour precipitation under future climate changeconditions.



in Canada’s North


F.6 Implications for engineeringWhat does this mean for structural engineers involved in Part 4 buildings and the trades designingPart 9 buildings? What changes in climate can engineers and the trades expect, and of what magnitude?With what certainty can a building be designed for the future, knowing that the environment it mustwithstand is changing relatively rapidly?

Engineers Canada has stated that “engineers, under their professional code of ethics, need to beinvolved in addressing the impacts of changing climate on infrastructure design and operations becauseit affects public safety and public interest.”24

As the climatic design values in codes and standards become more outdated relative to a changingclimate, designers face even greater challenges and professional risks25. While the prescriptive nature ofPart 9 might offer some legal protection to carpenters and architects who design according to itsmethodology, structural engineers designing Part 4 buildings will have no such protection in the eyes ofthe law, for professionals have always been held to a higher standard of accountability.

F.7 Climate change and designers’ risk“If you think mitigated climate change is expensive, try unmitigated climate change.”26

Since GHG emissions remain in the atmosphere for centuries to come, the costs and challenges of“managing the unavoidable impacts” of climate change will be greater without future reductions inglobal GHG emissions (i.e., mitigation). The Insurance Bureau of Canada has noted that climate changeis already affecting property and casualty insurance offerings and premiums in Canada27. The Canadianinsurance data26 indicates that the insured damages resulting from extreme weather grew from lossesof $200 million in 2006 to $1.2 billion in 2012, reflecting trends in global insurance losses.

Since climate change and its related impacts on infrastructure are now considered “reasonablyforeseeable”, the designers, builders, or operators who fail to take these impacts into account couldface potential litigation risk26. An article written by a leading legal expert appeared in the Bulletins ofseveral provincial and territorial engineering associations and highlighted some of these liabilityramifications for building designers. The article states28,

“It is becoming widely understood, for example, that in northern Canada, roads and air landingstrips are buckling because their foundations no longer rest on permanently frozen ground…Furthersouth, most Canadian provinces can expect, among other things, increasing precipitation; [sic]increased intensity of storm events, such as flooding, ice storms, heavy winds…more frequent…freezing and thawing cycles…There is a real risk that infrastructure stakeholders, i.e. those integrallyconnected with infrastructure ownership, planning, design, development and operation, could beliable to people who suffer personal injury or property damage caused by infrastructure that hasbeen adversely affected by climate change. In fact, the legal framework in Canada currently permitsa court, in the right circumstances, to find infrastructure stakeholders legally liable for personalinjury and property damage suffered by third parties, including, in the case of design professionals,on the basis of negligence… The law of negligence provides a means by which a person may seekcompensation for damages he or she suffered because of another’s failure to take reasonable care.For example, if the quantity of snow on the roof of a building causes the building’s roof to collapseresulting in personal injury, those injured may seek compensation... On the basis of Canadian caselaw, there are clear circumstances in which liability could be extended to design professionals,including engineers. There is an established duty of care between a design professional and anowner…Whether a design professional took reasonable care will usually be measured against theprofessional standard at the time the design was prepared. Following the standard practice of one’s



in Canada’s North


peers can be strong evidence of reasonable and diligent conduct but, importantly, it is notdeterminative. Rather, it is possible that the standard practice may itself be judged deficient incertain circumstances and, accordingly, adhering to such practice would be considered negligence.For example, given knowledge of climate change effects in a geographic area as a result of theproliferation of climate-related information and projection models, if the ‘standard practice’ at thetime of designing a specific type of infrastructure project is to ignore potential climate-changeeffects (despite widely available evidence), the standard practice itself may be negligent. Adheringto a deficient standard would be a breach of a design professional’s standard of care to an injuredperson”.

“In other words, liability might arise where a design professional complies with the minimumstandards set out in laws, codes and standards, but these standards fall below those of “areasonable person” in the legal sense. If a design professional is concerned that applicable laws,building codes or standards lack consideration for the impacts of climate change on aninfrastructure asset, a design professional should consider whether it is even reasonable to rely onthose laws, building codes or standards in the circumstances. In other words, would a “reasonableperson” simply rely on them in designing the infrastructure asset or would a reasonable person inthese circumstances design an infrastructure asset to a standard greater than the minimumstandard set forth?”28

In April, 2003, the Association of Professional Engineers of Nova Scotia (APENS) published a prescientposition statement on climate change (APENS Position on Climate Change)29. This statement has beenadopted by several other provincial and territorial engineering associations stating that:

“Climate change is an issue of risk management. Design and management approaches must beexpanded and plans developed for probable future impacts” while awareness becomes part ofprofessional “Due Diligence”. Thus, professional engineers need to become better informed, whichis part of professional development”29 and become “engaged in discussions regarding opportunitiesfor the mitigation of climate change and for impact/adaptation planning in anticipation of furtherclimate change and extreme weather events.”

F.8 Approaches for the design of new buildings, considering increasedsnow load risksRegardless of the approaches used to consider future climate change, it is important that uncertaintiesover the future climate not become a barrier to climate change risk reduction actions and lead toinaction. While uncertainties over the future environmental loads expected over the lifespan of a newbuilding could be a major challenge, it should not stop engineers from designing for future snow andother climate events. In reality, the costs and liability risks of inaction or delayed action will probably bemuch higher. Engineers have been relying on good judgment using factors of safety for centuries. It isstill the standard method of design for pre-limit states (such as working stress design).

Some proactive adaptation approaches are available, making use of engineering judgement. Theseincludea) No/low regrets* investments to update, reduce the uncertainty, and increase the accuracy of

current snow loads locally will enhance the resilience of new buildings into the future. Theseinvestments include measures to increase snow measurements (as outlined in this Standard) andto use good knowledge of local climate and community planning conditions in designconsiderations. For example, local effects from topography (location of the building in relation toobstructions) or the potential for taller buildings to be constructed within close proximity arealways necessary design inputs.31 And, consulting long-term residents could reveal vital



in Canada’s North


information on local and spatial variations in weather and climate that are not readily availablefrom the existing limited datasets. These low to no regret measures also include periodic snowoverload risk assessments of the building and enhanced maintenance, as outlined in this Standard.* The IPCC SREX document on climate extremes defines no and low regrets adaptation options as: “Measuresthat provide benefits under current climate and a range of future climate change scenarios… and areavailable starting points for addressing projected trends in exposure, vulnerability, and climate extremes (i.e.,these measures would also be of benefit even if climate change was not expected).

b) Enhance the safety factors (or adding a climate change adaptation factor) for environmental loads.The Government of the NWT applied the equivalent to enhanced safety factors to augment designsnow loads for design of public buildings15,17. Safety factors are used in engineering to account foruncertainties in the engineering, material properties, etc. and augment the structural capacity of abuilding beyond the expected loads or actual loads. In Canada, the safety factors used in codes andstandards typically do not account for uncertainties in the climatic design information. Until currenttrends and climate change models are further refined and the spatial and temporal resolution ofclimate models improved, enhanced (climate) safety factors greater than one could be used toaccount for the existing and increasing uncertainties in the climatic loads expected over thelifetime of the building. It is difficult to specify an additional or augmented climate change safetyfactor for future snow load values, particularly since the rate and amount of changes to climateand snow loads in Canada’s North depend critically on future increases in greenhouse gases and onthe complex interactions between several climate variables. Current and future trends in snowdepths, densities, rain on snow and snow loads (Ss) ̶ all backed by sufficient snow data forestimates of current trends̶ need to be tracked to guide development of climate change safetyfactors for snow loads32.

c) Increase the return periods of the snow loads used for design (i.e., allowing for increasedextremes). For example, the return periods associated with extreme snow loads could be increasedfrom the 1 in 50 to a 1 in 100 year recurrence event. While it is inherently difficult to estimate theprobability of historical extremes because there are so few such extreme events in the measuredrecord, it is considerably more difficult and unavoidably uncertain to estimate the probability ofeven more extreme events into the future. A simple approach, pending more reliable updated orfuture oriented snow load values, would be to refer to a higher return period value.

d) Planning for phased adaptation to future increases in snow loads through planned retrofits,enhancements or reinforcement, as possible, based on careful monitoring of snow loads (i.e.,ensuring that the total building structure will have capacity to withstand higher roof loads later).However, this option is risky since sudden or unexpected early changes in climate extremes arelikely. Phased adaptation approaches are more commonly considered in planning management offlooding or drainage risks.

Warmer winters might result in more extreme snowfalls, more frequent snow events, and might alsoinclude wetter or higher density snow conditions as well as risks of additional winter rain or freezingrain, further increasing the weight or load of already snow-overloaded roofs. Given the use of enhancedsafety factors or other measures to account for growing uncertainties in climatic loads, e.g., snow loads,what additional guidance can be given on the magnitude of the changes or additions?

F.9 Should engineers trust the science?The climate change science reported in the IPCC Fifth Assessment Reports (AR5) required the efforts ofmore than 800 selected authors and review editors from 85 countries. These IPCC reports weredeveloped under a rigorous, open, and transparent process in order to deliver a robust assessment. AllIPCC reports go through multiple rounds of review, with external reviews coming from as broad a rangeof experts as possible. Since scientific knowledge increased markedly in the period after the IPCC’s



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Fourth Assessment Report (AR4) was released in 2007, supporting statements and conclusions in thelatest report are stronger and more confident in identifying human GHG emissions as the primary driverof climate change. The AR5 report is considered to be the most detailed assessment of climate changeever, based on more data, containing more detailed regional climate projections, and is more confidentabout its conclusions than any previous assessment33.

In reality, the findings contained in the IPCC assessment reports often tend to be “conservative” due tostrict requirements for use of peer-reviewed science, delays in results reaching the peer-review andpublished state, and delays for peer-review of the IPCC reporting itself. As a result, many of the findingsdo not represent the latest research. Indeed, recent research findings indicate that projections of futurechanges in precipitation extremes could be underestimated by the climate models and that the climateextremes of the future could exceed current projections. In addition, the scientists contributing to thereport represent governments who, by nature, do not wish to promote irresponsible scientificstatements and tend to be cautious in drawing conclusions. For all of these reasons, engineers andapplied scientists can be reasonably confident that conclusions reported by the IPCC process can berelied upon. The “Precautionary Principle”34, combined with the engineers’ Code of Ethics (requiring anengineer to keep the public safety paramount), must provide guidance to the design approach.

F.10 Other concerns: Non-standard roofs, snow density, wind influencesQualified personnel who design, construct and operate buildings also need to consider other risksrelated to snow loads. For example, while snow load design procedures are covered for basic roof typesin Part 4 and the Commentary of the National Building Code of Canada, there are no standard protocolsbeyond specialized studies to guide the design of buildings for ice build-up, for ponding on flat roofs, orfor snow accumulation on roofs of non-standard shapes (e.g., valleys). Designing for these eventualitiesis left to the expertise of the design engineer.

Evidence also indicates that snow densities contributing to snow loads can vary over much greaterranges than the average values assumed in building code snow load calculations35. In reality, seasonallyaccumulated ground and roof snow densities tend to increase with snow depths, relatively warmertemperatures, wind packing, after many snowfall accumulations, and can be higher following heavierand wetter snowfall events. As can be seen from Table F.1 and Figure F.5, snow density values and unitweights for snow on the ground range from low values (new snow) to values approaching the density ofice and water (extremely wet dense).

In regions where winds are expected to increase under climate change (likely across many regions ofCanada’s North), the distribution of snow on the roof structure will be impacted and need to beconsidered during design36. In addition, for durability and maintenance purposes, higher frequencies offreeze/thaw cycles will probably deteriorate building envelopes at a greater rate, thus increasing thechance of damaging water ingress — further reducing a building’s lifespan. A higher frequency offreeze/thaw cycles might also increase the development of ice on the roof, especially if accompanied bymore rainfall on snow events. The roof’s thermal properties can also impact the roof snow loads, with awell-insulated or well-ventilated roof typically retaining more snow due to less melting of snow on theroof than a poorly insulated or ventilated roof. Note that codes and standards do not (and should not)allow reductions in roof snow loads from melting of snow as a result of heat escaping from buildings.



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Table F.1Typical densities of newly fallen snow, snowpacks, ice,

water and roof snow loads (kg/m3)37,38,39(See Clause F.10.)

Type of snow on ground Typical density (kg/m3)

New “dry” snow falling in still air 30–70

New wet snow falling in still air 100–200

Wind packed snow 250–400

Very wet, heavy snow (on ground) 400–800

Old snowpack 200–450 (see snow load densities below) — higher fordeep snowpacks

Firn (snow partly consolidated into ice) 400-800

Ice ~920

Water 1000

Roof snow load densities – assumed average for NBCC snow loadestimates

North of treeline 300;South of treeline 205 east of divide and 260-430 westof divide

Figure F.5The depth of a snowpack associated with a given snow load

(See Clause F.10.)

25.4 mm (1 in)of ice

254–304.8 mm (10–12 in)of fresh snow

76.2–127 mm (3–5 in)of packed/old snow

Dangerzone

1200+ mm(48 in)

610+ mm(24+ in)

102 mm(4+ in)

= =

Note: The depth of a snowpack associated with a given snow load (weight) will vary significantly with the densityof the snowpack and type of snow (age, compression for deeper snow, temperature conditions, atmospherichumidity, etc). (From Massachusetts Emergency Management Agency)

F.11 ConclusionsThis Annex is not intended to provide estimates of numerical coefficients for use in factors of safety. It isevident that good engineering judgment is needed in designing buildings that can stand up to theincreased loads expected over their planned lifespan.



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The increased cost of more resilient construction is minimal. While stronger beams, roof joists, trusses,hold-downs (for increased wind uplift), and columns will add some capital costs to construction, givenincreasing climatic loads, the increase will be minimal compared to the cost of lost lives, injuries,damages, retrofits, lawsuits, and re-building. Furthermore, with augmented “climate change” insurancepremiums that may be levied on buildings (as well as the increased cost of professional insurance), asavings in insurance can be anticipated for those buildings that can be demonstrated to have beendesigned for expected greater environmental loads than is the current practice. Further savings inoperating and maintenance budgets are anticipated due to avoidance of regular snow removal fromroofs as preventative measures—as well as less need for surveillance and regular assessments for snowoverloading.

In conclusion, designers of buildings have a responsibility to ensure that structures will withstand theenvironmental forces that can be reasonably anticipated. Legal opinion is increasingly supporting therequirement for climate change to be considered in the design of structures. The changes in climateresulting from accumulating greenhouse gases in our atmosphere will be with us for some time tocome, including an expectation for more severe or frequent high-impact weather events in the North(including heavier snow loads during some winters). Engineers are bound, both legally and ethically, toproduce buildings that are safe and will perform as expected. While designs for higher snow, ice, andrain loads will be somewhat more costly to construct, this extra cost might be expected to be partiallyreduced by lower insurance premiums and less maintenance costs. “Due diligence” practices suggestthat engineering judgment be used, based on the best climate analyses and science available todaywhile awaiting developments towards more precise scientific guidance on future snow loads. Thisengineering judgment should incorporate either a conservative factor of safety, an enhancement ofreturn periods, or other approaches to reflect the risks from increasing snow loads in the North.

F.12 References(1) Engineers Canada – Climate Change. Accessed from http://www.engineerscanada.ca/climate-change

(2) U.S. Army Corps of Engineers, 2011. U.S. Army Corps of Engineers Climate Change Adaptation Planand Report 2011. Washington, DC.. Accessed from http://corpsclimate.us/docs/usaceadaptnplanreport2011v02.pdf

(3) The IPCC concluded in its Special Report on Climate Extremes (SREX), published in 2012, that“Integration of local knowledge with additional scientific and technical knowledge can improve disasterrisk reduction and climate change adaptation (high agreement, robust evidence). See Note 5.

(4) IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis.Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel onClimate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia,V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York,NY, USA.

(5) IPCC, 2012: Managing the Risks of Extreme Events and Disasters to Advance Climate ChangeAdaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on ClimateChange [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, UK,and New York, NY, USA, 582 pp.

(6) Jones, Nicola, 2013. Climate assessments: 25 years of the IPCC, Nature, Volume 501:298–299.



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(7) Vincent, L.A. and É. Mekis, 2006. Changes in daily and extreme temperature and precipitationindices for Canada over the twentieth century. Atmosphere-Ocean, 44 (2): 177–193.

(8) Mekis, Éva and Vincent, Lucie A., 2011. An Overview of the Second Generation Adjusted DailyPrecipitation Dataset for Trend Analysis in Canada. Atmosphere-Ocean, 49: 2, 163-177.

(9) Zhang, X., J. Walsh, J. Zhano, U. Bhatt and M. Ikeda, 2004. Climatology and Interannual Variability ofArctic Cyclone Activity: 1948–2002. Journal of Climate, 17: 2300-2317.

(10) Lemmen, D.S., F. J. Warren, J. Lacroix and E. Bush (Eds), 2008. From Impacts to Adaptation: Canadain a Changing Climate. Government of Canada, Natural Resources Canada, Ottawa.

(11) Kunkel, K.E., T.R. Karl, H. Brooks, J. Kossin, J. Lawrimore, D. Arndt, L. Bosart, D. Changnon, S.L.Cutter, N. Doesken, 2013. Monitoring and understanding changes in extreme storms: state ofknowledge. Bulletin of the American Meteorological Society, 94:499–514. doi:http://dx.doi.org/10.1175/BAMS-D-11-00262.1.

(12) Knutti, R. and J. Sedlacek, 2013: Robustness and uncertainties in the new CMIP5 coordinatedclimate model projections. Nature Climate Change, 3:369-373. doi:10.1038/nclimate1716.

(13) Lenderink Geert and Erik Van Meijgaard, 2010. Linking increases in hourly precipitation extremes toatmospheric temperature and moisture changes. Environmental Research Letters, 5. doi:10.1088/1748-9326/5/2/025208.

(14) Berg, P., C. Moseley, J.O. Haerter, 2013. Strong increase in convective precipitation in response tohigher temperatures. Nature Geoscience, 6:181-185. doi:10.1038/ngeo1731.

(15) Bastedo, Jamie, 2007. On the Frontlines of Climate Change: What’s Really Happening in theNorthwest Territories. Prepared for The Honourable Nick G. Sibbeston, Senator for the NorthwestTerritories. Cygnus Environmental, Yellowknife.

(16) Changnon, S., D. Changnon and T. Karl, 2006. Temporal and Spatial Characteristics of Snowstormsin the Contiguous United States. Journal of Applied Meteorology and Climatology, 45: 1141–1155.

(17) GNWT, 2004. Roof snow overload risk estimation: PW&S/GNWT managed facilities/buildings. PublicWorks and Services, Government of the Northwest Territories, Yellowknife.

(18) Auld et al, 2008. “The Changing Climate and National Building Codes and Standards”. Adaptationand Impacts Research Section, Environment Canada, Toronto, Canada.

(19) Auld, H, 2008. Adaptation by Design: The Impact of Changing Climate on Infrastructure. Journal ofPublic Works and Infrastructure, 1 (3), May 2008. pp. 276-288.

(20) “high agreement, medium evidence” of benefits, as described by IPCC.

(21) Specifically, “Part 9 buildings” are defined as being no more than 600 sq. m in area and no morethan three storeys in height, which are used for major occupancies classified as Group C (residential),Group D (business and personal service), Group E (mercantile), and Group F, Divisions 2 and 3 (mediumand low hazard industrial).

(22) The four standard building materials: timber/lumber products, structural steel, reinforced concrete,and masonry.



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(23) Milly, P.C.D., J. Betancourt, M. Falkenmark, R. M. Hirsch, Z.W. Kundzewicz, D.P. Lettenmaier and R.J.Stouffer, 2008. “Stationarity is Dead: Whither Water Management?” Science, 319:573-574.

(24) http://www.engineerscanada.ca/climate-change

(25) The snow load data has been updated at least in part for the 2015 NBCC. The 2005 NBCC includedchanges from a 30-year return period to a 50-year return period for ground snow loads.

(26) From “The Costs of Not Dealing with Climate Change”, a presentation given at the Horton ModelUN, at Acadia University, by Heather Johannesen, Atlantic Institute for Sustainability, November 28,2002.

(27) National Round Table on Environment and Economy, 2011. Managing the Business Risks andOpportunities of a Changing Climate: A primer for Executives on Adaptation to Climate Change. NRTEE,Ottawa, 10 pp.

(28) Koval, Patricia, 2013. “Climate Change Risk: Is Liability Lurking For Professional Engineers?”Engineering Dimensions, January/February 2013, pp. 27-28 http://www.peo.on.ca/index.php/ci_id/20321/la_id/1.htm

(29) Presentation slides and Position Paper, 2003. By Einar Christensen, Carol Cunningham, ChrisFeetham, and Tom Livingston

(30) The IPCC SREX document on climate extremes defines no and low regrets adaptation options as:“Measures that provide benefits under current climate and a range of future climate change scenarios…and are available starting points for addressing projected trends in exposure, vulnerability, and climateextremes” (i.e. these measures would also be of benefit even if climate change was not expected).

(31) Indeed, snow that could be dumped or drifted from taller future structures must always beconsidered.

(32) Changes to design ground snow loads (snow component only) for the 2015 NBCC, consideringchanging extreme snow depths alone, increased Ss values for many northern communities by anaverage of 15% in the two decade period following the 1995 NBCC, with increases to the changed Ssvalues ranging from 3-35%. It is likely that snow loads will increase further in many communities oncechanges to snow densities and rain on snow are factored into future updates.

(33) Symon, C, 2013. Climate Change: Action, Trends and Implications for Business. The IPCC’s FifthAssessment Report,Working Group 1. University of Cambridge Programme for Sustainability Leadership,UK.

(34) “The most widely cited definition of the Precautionary Principle, and the one that is used in theCanadian Environmental Protection Act (CEPA 1999), emerged from the Rio Conference (1992) whichstates, ‘Where there are threats of serious or irreversible damage, lack of full scientific certainty shouldnot be used as a reason for postponing cost-effective measures to prevent environmental degradation.’The precautionary principle, which is essentially used by decision-makers in the management of risk,should not be confused with the element of caution that scientists apply in their assessment ofscientific data.” [From The Official Position on Climate Change by the Nova Scotia Association ofProfessional Engineers, April 17, 2003.]

(35) Building codes in past have assumed constant average snow density values. The current densityvalues (unit weights) used in ground snow load calculations are assumed to average 2.94 kN/m3 (300



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Kg/m3 or approximately 18.7 lb/ft3) for locations north of the treeline. South of the tree line, theaverage density is assumed as 2.01 kN/m3 east of the continental divide and ranges from 2.55 to 4.21kN/m3 west of the divide.

(36) Cheng, C., E. Lopes, C. Fu, and Z. Huang, 2014: Possible Impacts of Climate Change on Wind Gustsunder Downscaled Future Climate Conditions: Updated for Canada. J. Climate. doi:10.1175/JCLI-D-13-00020.1.

(37) “Preventing Roof Collapse Due to Heavy Ice and Snow”, Insurance Institute for Business and HomeSafety, Tampa, Fl. 2011, p. 2.

(38) Gray, D.M. and D.H. Male, 1981. Handbook of Snow: Principles, Processes, Management and Use.Pergamon Press, Toronto. 155.

(39) http://www.sciencelearn.org.nz/Contexts/Icy-Ecosystems/Looking-closer/Snow-and-ice-density



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Annex G (informative)Sample advisory on snow overload conditionsNote: This Annex is not a mandatory part of this Standard.

G.1 GeneralPotential snow overload conditions might require the issue of public advisories to warn the public ofpotential risks. Clause G.2 provides an example of a sample advisory that may be considered.

G.2 Sample advisory“Over the past number of months there has been a fairly heavy accumulation of snow in most parts ofthe NWT. Along with the additional snow fall we have also seen fairly high winds which can create aneven greater snow accumulation problem on buildings in the community. In past years, this has resultedin collapsed roofs in a number of communities. Some roof structures can be especially prone to highaccumulations of snow due to drifting. To avoid the collapse of a roof it is important to inspect each oneof your buildings to determine the amount of snow accumulation on the roof.

Determine the maximum snow load capacity of your roof. Snow load is measured in kilograms persquare metre (kg/m2) or pounds per square foot (psf) . For example, 200 mm (10 in) of snow isapproximately 24 kg/m2 (5 lb/ft2). Resources are available to help you determine the snow load capacityof your roof, including the building blueprints and specifications, the construction date of the building,and the structural engineers involved in the original design. It is important to know the snow density onthe ground to help determine the density of the snow on the roof of the structure. This can be doneusing snow tube density measurements in the community in accordance with CSA S502-15, ManagingChanging Snow Load Risks for Buildings in Canada’s North.

Before removing snow from a roof:a) Examine the building for visible signs of structural distress, such as twisting, bending, or cracking.

Consult a structural engineer if necessary;b) Before removing snow from a roof, cordon off the deposit area on the ground and have an

employee monitor the area to ensure that pedestrians or vehicles do not enter this zone;c) Avoid producing an uneven or concentrated snow load on the roof during snow removal;d) If snow blowers are used on the roof, ensure the blades are raised high enough to prevent damage

to the roof cover; ande) Watch for ponding as snow compresses and absorbs rain. The increased weight can create

depressions that may not drain.

Prior to allowing employees to physically remove snow from the roof of a structure, implement safesnow removal procedures.”



Documents

Managingchangingsnowloadrisksfor buildingsinCanada’sNorth · CAN/CSA-S502-14 NationalStandardofCanada Managingchangingsnowloadrisksfor buildingsinCanada’sNorth Licensed for/Autorisé