---
title: "How Snow and Ice Affect Buildings | AVANORTH"
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last_updated: "2026-03-09T15:39:03.766Z"
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description: "How snow loads, ice dams, and freeze-thaw cycles impact building structures in Canada. Prevention strategies for roofs, walls, and foundations."
"og:description": "How snow loads, ice dams, and freeze-thaw cycles impact building structures in Canada. Prevention strategies for roofs, walls, and foundations."
"og:title": "How Snow and Ice Affect Buildings"
"twitter:description": "How snow loads, ice dams, and freeze-thaw cycles impact building structures in Canada. Prevention strategies for roofs, walls, and foundations."
"twitter:title": "How Snow and Ice Affect Buildings"
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AVANORTH Home
**Construction Tips**·February 1, 2026· 4 min read
# **How Snow and Ice Affect Building Structures**
Canadian winters bring heavy snow loads and freeze-thaw cycles that test every building. Learn how snow and ice impact roofs, walls, and foundations over time.
**AVANORTH Team**
AVANORTH Construction
## Snow Loads: A Structural Reality
In Canada, snow is not just a nuisance. It is a structural load that buildings must be engineered to support. The National Building Code of Canada specifies design snow loads based on geographic location, ranging from about 1.0 kPa in southern Ontario to over 5.0 kPa in parts of Quebec, northern Ontario, and the Atlantic provinces. These loads translate to significant weight: a 1.0 kPa snow load on a 200-square-metre roof is 20,000 kilograms, roughly the weight of 12 mid-size cars.
Snow loads are not uniform. Wind redistributes snow on roofs, creating drift loads at roof-to-wall junctions, around parapets, near mechanical equipment, and on lower roofs adjacent to taller structures. These drift loads can be two to three times the ground snow load. Structural engineers must account for both uniform snow loads and drift patterns when designing roof structures.
## Ice Dams on Roofs
Ice dams form when heat escaping through the roof melts snow on the upper portion of the roof. The meltwater runs down to the eave, where the roof surface is colder (it overhangs beyond the heated building envelope), and refreezes. Over time, a ridge of ice builds up at the eave, trapping water behind it. This water backs up under the shingles and can leak into the building.
Preventing ice dams requires addressing the root cause, heat escaping through the roof:
- **Adequate attic insulation:** R-50 to R-60 in the attic floor prevents heat from reaching the roof deck
- **Proper attic ventilation:** Continuous soffit-to-ridge ventilation keeps the roof deck cold and uniform in temperature
- **Air sealing:** Seal all penetrations between the heated living space and the attic (pot lights, plumbing stacks, electrical boxes, the attic hatch) to prevent warm air leakage
- **Ice and water shield membrane:** A self-adhesive waterproof membrane installed on the first 900 mm to 1200 mm of the roof deck above the eave provides backup protection if some ice damming occurs
## Freeze-Thaw Damage to Masonry
Brick, stone, and concrete block absorb moisture. When that moisture freezes, it expands and creates internal pressure that progressively deteriorates the masonry. This manifests as:
- **Spalling:** The face of the brick or stone flakes off, exposing the softer interior
- **Mortar joint failure:** Freeze-thaw cycles break down mortar joints, opening paths for more moisture to enter
- **Efflorescence:** White salt deposits on the masonry surface indicate moisture is moving through the wall and carrying dissolved salts to the surface
Prevention starts with proper wall design: an air gap behind the brick veneer allows moisture to drain, weep holes at the base of the brick let water exit, and flashing at window heads and shelf angles redirects water outward before it can enter the wall assembly.
## Foundation Heaving
As discussed in our earlier post on frost lines, freezing soil can exert enormous upward force on foundations. But ongoing freeze-thaw cycles also cause cumulative damage to exposed foundation surfaces. Concrete that is not air-entrained will progressively deteriorate from surface scaling when exposed to freeze-thaw and de-icing salts.
Protection measures include:
- Using air-entrained concrete for all exposed foundation surfaces
- Applying waterproof coatings to above-grade foundation walls
- Maintaining proper grading to direct water away from the foundation
- Avoiding the use of salt-based de-icers near concrete surfaces in the first year after placement
## Snow Removal Considerations
Building owners and managers should have snow management plans that include:
- Maximum permissible snow depth on the roof before removal is required
- Designated snow storage areas on the property that do not block drainage paths
- Spring drainage plans to manage meltwater from accumulated snow piles
- Regular inspection of roof drains and scuppers to ensure they are not blocked by ice
## Designing for Winter Resilience
Buildings in Ontario should be designed assuming they will face 50 or more freeze-thaw cycles every winter. This means specifying materials and assemblies that tolerate moisture cycling, providing drainage paths at every intersection, and maintaining the building envelope to prevent water infiltration.
At AVANORTH, we design and build for the full range of Canadian winter conditions. Our material specifications, detail drawings, and construction practices all account for the reality that snow and ice are persistent forces that buildings must resist throughout their service life.
#snow-load #winter #structural
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