What snow actually weighs on a Canadian roof
Snow weight by type
| Snow type | Density | Weight per 10 cm depth (per sq m) |
|---|---|---|
| Fresh dry powder | ~50 kg/m³ | 5 kg / sq m |
| Fresh wet snow | ~150 kg/m³ | 15 kg / sq m |
| Settled snow (1–2 weeks old) | ~250 kg/m³ | 25 kg / sq m |
| Compacted snow (multiple storms layered) | ~400 kg/m³ | 40 kg / sq m |
| Wet snow + ice layer | 500–800 kg/m³ | 50–80 kg / sq m |
Roof area math
A 100 sq m roof (typical single-family detached) with 60 cm of compacted wet snow:
- Total snow load: ~24,000 kg (24 tonnes)
- Equivalent to: 4–5 mid-size cars sitting on the roof
- Design margin: typically 20–40 % above expected maximum (varies by region and code era)
National Building Code design loads by region
Snow load by Canadian region
| Region | Design load (ground snow) | Typical roof design |
|---|---|---|
| Toronto, Vancouver | 1.6–2.2 kPa | 80–110 lb / sq ft |
| Calgary, Edmonton | 2.0–2.6 kPa | 100–130 lb / sq ft |
| Montréal, Québec City | 2.4–3.0 kPa | 120–150 lb / sq ft |
| Saguenay, Saint John, St. John's | 2.8–3.6 kPa | 140–180 lb / sq ft |
| Sherbrooke, Saint-Maurice valley | 2.6–3.4 kPa | 130–170 lb / sq ft |
| Nunavut, Yukon, NWT | 3.0–5.0+ kPa | 150–250+ lb / sq ft |
Where the load exceeds design
Snow load tends to exceed design capacity on:
- Flat or low-slope sections (under 4:12 pitch) — snow does not slide off
- Leeward sides of roof valleys — wind drifts deposit 2–3x the average load
- Behind dormers — snow piles against vertical walls
- Around HVAC penetrations — drift accumulates against equipment
- Adjacent to taller structures — wind shadow drift loading
Warning signs that mean clear within 24 hours
Structural warning signs
- Visible sagging of the roof line — call immediately
- Doors or windows that suddenly stick or won't close — frame distortion from load
- Cracking sounds from the attic at night — wood members yielding
- Cracked plaster along interior wall-ceiling junctions
- Roof rafters or trusses visibly deflected more than 1 cm at midspan
Ice damming warnings
- Icicles longer than 60 cm at the eaves — ice dam present
- Water staining inside the building near exterior walls — meltwater backup
- Ice visible behind shingles at the eaves
- Visible ice ridge along the eave line over 5 cm thick
- 01Snow > 60 cm on a flat or low-slope roof: call for assessment
- 02Snow + ice dam at eave: call within 24 hours
- 03Audible structural sounds: evacuate and call within 4 hours
- 04Visible deflection: evacuate and call immediately
- 05Heritage building, any snow load: monitor weekly during winter
How a professional crew clears safely
Equipment that won't damage the roof
- Poly-edge snow rake — operator stays on the ground (safest, primary tool)
- Fall-arrest-equipped manual clearing — for two-storey and commercial roofs
- Low-pressure hot-water steam — for ice dam removal (Steam Power Cleaner units)
Equipment to never use
- Power snow blowers — destroy shingles, membrane, gutters in minutes
- Power shovels or skid-steer attachments — same
- Ice chipping tools — strip shingles and shorten roof life 5–15 years per event
- Salt or calcium chloride applied directly to shingles — corrodes flashing and damages shingle asphalt
Cost in Canada (2025–26)
| Service | Cost |
|---|---|
| Single-storey roof rake from ground | $450–$700 |
| Two-storey or steep-slope (fall arrest) | $700–$1,200 |
| Commercial low-slope | $0.45–$1.20 / sq ft |
| Ice dam removal (per dam) | $350–$900 |
Questions, answered.
How much snow can a typical Canadian roof safely hold?
A residential roof built to current National Building Code can hold the regional design load — Toronto 170 kg/m², Montréal 210 kg/m², Calgary 115 kg/m², Halifax 250 kg/m², St. John's 340 kg/m². In fresh snow that's 1.5-3 metres deep; in wet snow + ice it's 35-70 cm. Pre-1970 buildings hold roughly 60-75% of those values. Heritage and pre-WW2 industrial buildings should be monitored more frequently.
When should I call a crew to clear my roof?
Call within 24 hours if: snow exceeds 60 cm on a flat/low-slope roof, you see an ice dam over 10 cm thick at the eaves, doors or windows are sticking, or you notice new diagonal cracks in interior drywall. Call within 4 hours if you hear creaking or popping from the roof structure. Evacuate and call immediately if you see visible deflection of the roof line. Rain-on-snow events are the highest-risk profile and warrant pre-emptive clearing.
Can I clear my roof myself with a snow rake?
For one-story residential roofs, a polypropylene snow rake operated from the ground can remove the bottom 1-2 metres of snow safely. Beyond that height, falls from ladders and rooftops are the #1 winter injury for Canadian homeowners. Commercial flat roofs and residential roofs above one story require professional crews with fall-arrest gear. The cost of a fall — fracture, head injury, time off work — dwarfs the $250-450 crew callout.
What does professional roof clearing cost in Canada?
Residential single-story roof clearing runs $200-450 depending on size and access. Two-story homes are $400-800. Commercial flat roofs are quoted per square metre — typically $1.20-2.40/m² for clearing, with a $400-650 minimum callout. Ice dam steaming adds $300-650 depending on dam thickness and length. Emergency same-day callouts (during or immediately after a storm) carry a 50-100% premium.
Are ice dams as dangerous as snow load?
Ice dams pose two distinct risks. Structural: a 20 cm ice dam over a 12 m eave concentrates 4+ tonnes on a 2 m wide strip at the roof edge — enough to pull down gutters, tear fascia, and in extreme cases collapse verandas. Water damage: meltwater backs up under the shingles and runs down inside the wall cavity, causing rot, insulation damage, and mold that often goes undiscovered until spring. Ice dams should be steam-removed (not chipped) within 24-48 hours of formation.