Snow Load Tables Canada — Ground Snow Load by Province

What is ground snow load (S_s)?

Ground snow load (S_s) is the 50-year return period snow load at ground level for a given location, measured in kiloPascals (kPa). It represents the weight of accumulated snow on the ground that has a 2% probability of being exceeded in any given year. The values are set by the National Building Code of Canada (NBCC 2020) in Appendix C, Table C-2.

Ground snow load is not the same as roof snow load. Roof snow load accounts for roof slope, wind exposure, accumulation patterns, and a rain-on-snow component (S_r). The NBCC 2020 formula for specified roof snow load is:

S = I_s × [S_s × (C_b × C_w × C_s × C_a) + S_r]

Where C_b is the basic roof snow load factor (0.8 for most roofs), C_w is wind exposure, C_s is slope factor, and C_a is accumulation factor. To apply this formula to your specific roof, use the Roof Snow Load Calculator →

The rain-on-snow load (S_r) is an associated rain load added to the ground snow load when calculating roof snow load. It is higher in coastal regions (BC, NS, NL) where mid-winter rain events are common, and lower in the continental interior where winter precipitation is almost entirely snow.

How much snow can a roof hold?

A common practical question is how much snow depth corresponds to a given snow load. Snow density varies considerably — fresh light snow weighs roughly 100 kg/m³ (0.10 kPa per 10 cm depth), while wet packed snow can reach 500 kg/m³ (0.50 kPa per 10 cm depth). As a rough guide:

A residential roof designed to the NBCC snow load for Toronto (S_s = 1.4 kPa) can typically handle roughly 50–140 cm of accumulated snow depending on snow type — but the roof snow load (after applying slope and exposure factors) is always less than the ground snow load value in the table below. Have a structural engineer assess any roof you suspect is overloaded.

Ground snow load tables by province

All values from NBCC 2020 Appendix C, Table C-2. S_s = specified ground snow load (kPa). S_r = associated rain load (kPa). For cities not listed, consult your local authority having jurisdiction (AHJ) or a licensed engineer — municipal snow load maps may provide site-specific values.

How to use these values

The S_s value from the table is the starting input for roof snow load design — it is not the final design load. You must apply the NBCC 2020 Clause 4.1.6.2 formula with the appropriate roof factors before sizing roof members or checking an existing structure.

• For a flat or low-slope roof (≤ 30°), C_s = 1.0 and the full ground snow load applies
• For a steep roof (≥ 70°), C_s = 0 — no snow accumulation assumed
• Wind-exposed locations use C_w = 0.75, reducing the design load by 25%
• Valleys and areas prone to accumulation use C_a > 1.0, increasing the design load

Provincial building code references

Most provinces adopt the NBCC with amendments. The ground snow load values in NBCC Appendix C apply across all provinces unless a provincial amendment specifies otherwise. For permit submissions, reference the provincial building code edition adopted in your jurisdiction:

BC uses site-specific snow load maps for some regions where Appendix C values are not available — particularly in mountain communities and coastal inlets. Contact your local AHJ or a licensed engineer for site-specific values.