CSA S505:20 Techniques for Considering High Wing and Snow Drifting and their Impact on Northern Infrastructure

Canadian Standards Association (CSA) Group received funding for the development of this Standard from the Standards Council of Canada, as part of the Northern Infrastructure Standardization Initiative with input from the Northern Advisory Committee (NAC).

This Standard was prepared by the Subcommittee on High Winds and Snow Drifting for Northern Infrastructure and Climate Change, under the jurisdiction of the Technical Committee on Northern Built Infrastructure and the Strategic Steering Committee on Construction and Civil Infrastructure, and has been formally approved by the Technical Committee.

This Standard addresses risks to northern infrastructure due to wind, snow, and snow drifting. It incorporates the following themes, all in the context of Canada’s North and climate change:

  • Weather data, climate variables, and relevant projections and forecasts
  • Reducing the risk of damage
  • Climate adaptation strategies
  • Improving function and accessibility
  • Design construction techniques


This Standard provides guidance to northern infrastructure designers, builders, operators, and owners to address the increased risk of damage to the built environment, including the potential effects of climate change (specifically, risks from higher and more frequent wind loads and associated snow drifting) in Canada’s North. Canada’s North, as defined in this Standard, consists of the territories of Yukon, Nunavut, and the Northwest Territories (NWT), along with the northern portion of Nunavik (“great land”) in the north of Québec, which juts out between Ungava Bay and Hudson Bay (where seven Inuit communities are located above the 54th parallel around the perimeter of the Ungava Peninsula).

Understanding and Assessing Impact

CSA undertook a series of approaches to understand how climate change will impact the design of local infrastructure in the North: local traditional knowledge and weather data stations. Local traditional knowledge can supplement and is often the only source of weather and climate data in a specific area of the North. It is important that local knowledge is used in the design of new infrastructure and upgrades to existing infrastructure. 

Local and traditional knowledge includes the following examples: 

  • The Denesoline of Lutsel K’e Dene First Nation Elders (living near the Great Slave Lake, NWT) have observed abnormal and unstable weather, such as unpredictable storms and unusually warm temperatures, and they have noticed an increase in lightning storms. 
  • The Sahtu Dene around the Great Bear Lake, NWT, have noted that in days past, snow would accumulate over many series of snowfalls, whereas nowadays, they note that it more likely arrives via unique heavy storm events. 
  • Residents of Québec’s Ivujivik (in Nunavik) have reported stronger winds and more storms per year, and both Inuit experts and scientists in Clyde River, Nunavut, note that wind velocity has risen in recent years, and the wind direction is far more variable and unpredictable. 

Climate data and future climate data modelling were also utilized to better understand the impacts on northern communities and infrastructure. Future climate modelling considered a timeline out to 2100 and two climate scenarios (RCP 2.6 and 8.5) and considered: 

  • Annual mean temperature change
  • Changes in mean annual and seasonal precipitation
  • Changes in snowpack
  • Permafrost thaw
  • Changes to sea ice and a reduction of ice cover
  • Sea-level rise

Snowpacks in the North are expected to become more saturated with water than in the past. This might be due to increased rainfall during warmer springs, warmer snow days, or increased precipitation as snow. Data from the North American insurance industry has revealed that roof failure due to concentrated snow drift loads is three times more likely to occur than collapse due to uniformly distributed snowfall loads across the entire roof.

Identifying Actions

The standard breaks down several actions Northern municipalities can take to better prepare their communities for the impacts of stronger and more frequent windstorms and shifting snowfall patterns. Identifying buildings and critical infrastructure at risk, retrofitting existing buildings, rain and snow monitoring, monitoring and risk analysis of snow drift patterns, community map and action plan for snow drifting and drainage, identifying post-disaster buildings, constructing snow fences, conducting snow drift studies, and more.

A community map and action plan should be created to identify critical life safety and essential services where resiliency is needed. The map and action plan should consider issues such as the following:

  • Emergency access and routes
  • Truck services (water, oil, and fuel)
  • Entrances and exits for buildings classified as high importance and post-disaster
  • Roof and deck profiles for buildings classified as high importance and post-disaster
  • Air intakes and exhausts
  • Critical infrastructure network

The map and action plan should make note of the horizontal extent of drifts, maximum recorded depth of drifts, and specific notes accompanying each drift as needed, drawn from the experience of maintenance and equipment operators or community public works foreperson. At-risk buildings or elements can include:

  • Buildings with visible damage
  • Buildings with a change of use or occupancy
  • Isolated buildings
  • Buildings under construction
  • Buildings with large opening(s) such as windows and doors
  • Buildings with exterior appurtenances susceptible to damage

At-risk infrastructure components can include:

  • Road networks
  • Telecommunication and power lines
  • Towers and poles
  • Above-ground water lines
  • Utilidors
  • Satellite dishes
  • Wind turbines
  • Photovoltaic panels


Retrofitting existing buildings for increased wind and snow drifting. Repeated wind forces can weaken a structure, rendering it more susceptible to failure during some future windstorm. At the same time, snow drifting can damage a building in a way that could make it too unstable for use or block entrances, ventilation openings, or other access points that could affect function and accessibility.

The following wind effects should be considered when assessing existing buildings:

  • Torsion
  • Uplift
  • Wracking
  • Fatigue
  • Bending
  • Pressure
  • Material failure
  • Areas adjacent to parapets or other elements such as HVAC equipment, PV arrays, penthouses, clerestories, etc.
  • Roofs that are within 10 m horizontally of other taller structures
  • Roof areas such as decks, roof steps, and valleys.

The building assessment might indicate the need to retrofit building envelopes and structures. These retrofits can include the following:

  • Anchorage of structure or elements
  • Protection of openings
  • Structural reinforcements (lateral or vertical load systems)
  • Air and moisture infiltration
  • Impact debris potential
  • Modification to the building form

Adding a canopy, wind deflector, or windscreen can mitigate frequent localized snow drift problems on existing buildings. Snow fences can be an effective barrier to blowing and drifting snow by reducing the wind speed and lowering its ability to carry snow beyond the fence. The most significant snow accumulation forms on the downwind side of the fence, far away from the roadway. Typically snow fences should be perpendicular to prevailing winds. On level terrain, the length of the downwind drift created by a snow fence can be upwards of 35 times the height of the fence. The upwind drift can reach a distance of 15 times the height of the snow fence. In Arctic regions, snow fences can range from 2 to 5 m in height and provide community-wide protection from severe snow drifting around buildings.

Snow fence design and siting must be coordinated with community land-use planning to accommodate snow accumulation setbacks on the windward and leeward sides of the fence that must remain vacant and unobstructed.

The Standard also identifies other key infrastructure impacted by snowdrifts and provides expertise on reducing snowdrifts through road construction best practices and plowing considerations. Additionally, the Standard provides actions to reduce snow/ice damming affecting bridges and roads over culverts.

Outcomes and Monitoring Progress

While the Standard does not provide any specific monitoring practices, it does recommend continuing to measure snowfall and snow drift patterns to identify where snow is falling, drifting patterns, and the weight of the snow. This monitoring will help identify buildings or infrastructure at risk, as well as the efficacy of snow fence placement.

The Standard recommends that when considering engineering design for new infrastructure, local elders should be consulted about snow block behaviour during spring freshet and variables such as snow drift heights, riverbank height, river height and flow speed, and prevailing winds.

Finally, the Standard recommends a proactive approach to climate change adaptation. It is important that uncertainties regarding the future climate not become a barrier to climate change risk reduction actions and lead to inaction. While uncertainties about future environmental loads expected over the lifespan of new infrastructure can be a significant challenge, it should not stop buildings from being designed for future changes in wind, snow, and other climate events. In reality, the costs and liability risks of inaction or delayed action will probably be much higher.

Some proactive adaptation approaches are available, making use of engineering judgment. These include the following:

  • No/low regrets investments to update, reduce the uncertainty, and increase the accuracy of current wind and snow loads locally will enhance the resilience of new infrastructure into the future
  • Enhance the safety factors (or add a climate change adaptation factor) for environmental loads
  • Increase the return periods of the wind and snow loads used for design
  • Planning for phased adaptation to future increases in wind and snow loads through planned retrofits