Roof Snow Loads by City: The Building Code Design Load in 30 Canadian Cities, and When a Roof Needs Clearing
What a Code-Built Roof Is Designed to Carry, Translated Into Snow You Can See
By
Published: November 14, 2026
Fact-checked · , including nrc-publications.canada.ca, National Research Council Canada
Credit: Shutterstock
Key Takeaways
•The design roof snow load for a house ranges from 1.00 kPa in Toronto, Calgary, Regina and Victoria to 2.58 kPa in Québec City, and the building code never lets it fall below 1 kPa.
•Depth is a poor measure of load: the same design figure equals roughly a metre or more of fresh snow, but only 20 to 65 cm of wet, rain-soaked snow.
•Official Canadian guidance points one way: watch for signs of stress indoors, rake from the ground if anything, and leave rooftop work to people with fall protection.
Most homeowners think about roof snow as a depth. The building code thinks about it as a weight. Those two ideas only meet once you know how dense the snow is, and density can change fivefold between a cold January powder and a March snowpack that has been rained on.
This guide puts numbers on both sides. It takes the ground snow load and rain load printed in the building code for 30 Canadian cities, runs them through the formula the code prescribes for houses, and reports the result: the snow load a code-built house roof in that city is designed to carry. Then it converts each figure into approximate depths of fresh, settled and wet snow, so the number means something from the driveway.
A design load is a minimum that builders must meet. It is not a prediction of when any particular roof will fail, and it is not a clearing threshold. No table can tell you that your roof is fine. What it can do is show why two cities an hour apart are built to different standards, why a rain-on-snow week matters more than a record snowfall, and which signs mean it is time to call a professional.
How the code turns ground snow into a roof load
The starting point is a table at the back of the code. Appendix C of the National Building Code lists climatic design data for several hundred locations, including two snow figures for each: the ground snow load, written S<sub>s</sub>, and an associated rain load, S<sub>r</sub>. Both are 1-in-50-year values in kilopascals (kPa). One kilopascal is about 20.9 pounds per square foot, or roughly 102 kilograms resting on every square metre.
Houses and small buildings fall under Part 9 of the code, which uses a simplified calculation. Under Article 9.4.2.2 of the National Building Code of Canada 2020, the specified snow load is S = C<sub>b</sub> × S<sub>s</sub> + S<sub>r</sub>. The basic snow load roof factor, C<sub>b</sub>, is 0.45 where the entire width of the roof does not exceed 4.3 m and 0.55 for all other roofs. A second sentence sets a floor: in no case shall the specified snow load be less than 1 kPa.
The width condition does most of the sorting. A house roof is wider than 4.3 m, so it takes 0.55. The lower factor applies to narrow roofs such as a small porch or a garden shed. The table below uses 0.55 throughout.
The worksheet for one city
Take Ottawa. The code lists Ottawa (City Hall) at S<sub>s</sub> = 2.4 kPa and S<sub>r</sub> = 0.4 kPa.
Multiply the ground snow load by the roof factor: 0.55 × 2.4 = 1.32 kPa.
Add the rain load: 1.32 + 0.4 = 1.72 kPa.
Check the floor: 1.72 is above 1 kPa, so the specified roof snow load is 1.72 kPa, about 36 pounds per square foot.
Now run Calgary through the same steps. With S<sub>s</sub> = 1.1 and S<sub>r</sub> = 0.1, the arithmetic gives 0.71 kPa. That is below the floor, so the code raises it to 1.00. Calgary's design figure is the minimum, not the calculation.
From kilopascals to centimetres
Depth equals load divided by specific weight. The code supplies the specific weights itself. Appendix C states that new snow is usually assumed to average 1 kN/m³ in Canada, and that old snow generally ranges from 2 to 5 kN/m³. In everyday units, that is about 100 kg per cubic metre for fresh snow and 200 to 500 kg for snow that has settled, thawed, refrozen or absorbed rain.
This guide groups that range into three bands: fresh snow at 1.0 kN/m³, settled snow at 2.0 to 3.0, and wet or dense snow at 4.0 to 5.0. The banding is ours; the endpoints are the code's. Ottawa's 1.72 kPa works out to about 170 cm of fresh snow, 55 to 85 cm of settled snow, or 35 to 45 cm of wet snow. Same load, three very different pictures.
Getting a roof ready for that load starts well before the first storm, and the Canadian snow-ready roof guide covers the preparation side in detail.
The starting point is a table at the back of the code. Appendix C of the National Building Code lists climatic design data for several hundred locations, including two snow figures for each: the ground snow load, written S<sub>s</sub>, and an associated rain load, S<sub>r</sub>. Both are 1-in-50-year values in kilopascals (kPa). One kilopascal is about 20.9 pounds per square foot, or roughly 102 kilograms resting on every square metre.
Houses and small buildings fall under Part 9 of the code, which uses a simplified calculation. Under Article 9.4.2.2 of the National Building Code of Canada 2020, the specified snow load is S = C<sub>b</sub> × S<sub>s</sub> + S<sub>r</sub>. The basic snow load roof factor, C<sub>b</sub>, is 0.45 where the entire width of the roof does not exceed 4.3 m and 0.55 for all other roofs. A second sentence sets a floor: in no case shall the specified snow load be less than 1 kPa.
The width condition does most of the sorting. A house roof is wider than 4.3 m, so it takes 0.55. The lower factor applies to narrow roofs such as a small porch or a garden shed. The table below uses 0.55 throughout.
The worksheet for one city
Take Ottawa. The code lists Ottawa (City Hall) at S<sub>s</sub> = 2.4 kPa and S<sub>r</sub> = 0.4 kPa.
Multiply the ground snow load by the roof factor: 0.55 × 2.4 = 1.32 kPa.
Add the rain load: 1.32 + 0.4 = 1.72 kPa.
Check the floor: 1.72 is above 1 kPa, so the specified roof snow load is 1.72 kPa, about 36 pounds per square foot.
Now run Calgary through the same steps. With S<sub>s</sub> = 1.1 and S<sub>r</sub> = 0.1, the arithmetic gives 0.71 kPa. That is below the floor, so the code raises it to 1.00. Calgary's design figure is the minimum, not the calculation.
From kilopascals to centimetres
Depth equals load divided by specific weight. The code supplies the specific weights itself. Appendix C states that new snow is usually assumed to average 1 kN/m³ in Canada, and that old snow generally ranges from 2 to 5 kN/m³. In everyday units, that is about 100 kg per cubic metre for fresh snow and 200 to 500 kg for snow that has settled, thawed, refrozen or absorbed rain.
This guide groups that range into three bands: fresh snow at 1.0 kN/m³, settled snow at 2.0 to 3.0, and wet or dense snow at 4.0 to 5.0. The banding is ours; the endpoints are the code's. Ottawa's 1.72 kPa works out to about 170 cm of fresh snow, 55 to 85 cm of settled snow, or 35 to 45 cm of wet snow. Same load, three very different pictures.
Getting a roof ready for that load starts well before the first storm, and the Canadian snow-ready roof guide covers the preparation side in detail.
The design snow load in 30 Canadian cities
The table ranks 30 cities from the highest specified roof snow load to the lowest. Every S<sub>s</sub> and S<sub>r</sub> value was read from the code document named in the last column, not from a secondary website. Depths are rounded to the nearest 5 cm and are approximate by nature.
30 rows · 9 columnsTap a header to sort
Québec City
Que.
3.6
0.6
2.58
260
85–130
50–65
NBC 2020, p. C-30
Corner Brook
N.L.
5.3†
0.9†
2.54
255
85–125
50–65
NBC 2025, p. C-42
St. John's
N.L.
4.4†
1.1†
2.35
235
80–120
45–60
NBC 2025, p. C-42
Fredericton
N.B.
3.1
0.6
2.31
230
75–115
45–60
NBC 2020, p. C-33
Moncton
N.B.
3.0
0.6
2.25
225
75–110
45–55
NBC 2020, p. C-33
Charlottetown
P.E.I.
2.7
0.6
2.09
210
70–105
40–50
NBC 2020, p. C-34
Prince George
B.C.
3.4
0.2
2.07
205
70–105
40–50
NBC 2020, p. C-13
Thunder Bay
Ont.
2.9
0.4
2.00
200
65–100
40–50
SB-1 (2024), Table 2
Saguenay
Que.
2.7
0.4
1.89
190
65–95
40–45
NBC 2020, p. C-31
Saint John
N.B.
2.3
0.6
1.87
185
60–95
35–45
NBC 2020, p. C-33
Montréal (City Hall)
Que.
2.6
0.4
1.83
185
60–90
35–45
NBC 2020, p. C-30
Sherbrooke
Que.
2.2
0.6
1.81
180
60–90
35–45
NBC 2020, p. C-32
Iqaluit
Nvt.
2.9
0.2
1.80
180
60–90
35–45
NBC 2015, Table C-2
Barrie
Ont.
2.5
0.4
1.78
180
60–90
35–45
SB-1 (2024), Table 2
Sudbury
Ont.
2.5
0.4
1.78
180
60–90
35–45
SB-1 (2024), Table 2
Ottawa (City Hall)
Ont.
2.4
0.4
1.72
170
55–85
35–45
SB-1 (2024), Table 2
Halifax
N.S.
1.9
0.6
1.65
165
55–80
35–40
NBC 2020, p. C-33
London
Ont.
1.9
0.4
1.45
145
50–70
30–35
SB-1 (2024), Table 2
Yellowknife
N.W.T.
2.2
0.1
1.31
130
45–65
25–35
NBC 2020, p. C-36
Winnipeg
Man.
1.9
0.2
1.25
125
40–60
25–30
NBC 2020, p. C-19
Whitehorse
Y.T.
2.0
0.1
1.20
120
40–60
25–30
NBC 2020, p. C-35
Vancouver (City Hall)
B.C.
1.8
0.2
1.19
120
40–60
25–30
NBC 2020, p. C-14
Edmonton
Alta.
1.7
0.1
1.04
105
35–50
20–25
NBC 2020, p. C-15
Kelowna
B.C.
1.7
0.1
1.04
105
35–50
20–25
NBC 2020, p. C-12
Saskatoon
Sask.
1.7
0.1
1.04
105
35–50
20–25
NBC 2020, p. C-18
Hamilton (below the escarpment)
Ont.
1.1
0.4
1.01
100
35–50
20–25
SB-1 (2024), Table 2
Calgary
Alta.
1.1
0.1
1.00*
100
35–50
20–25
NBC 2020, p. C-15
Regina
Sask.
1.4
0.1
1.00*
100
35–50
20–25
NBC 2020, p. C-18
Toronto (City Hall)
Ont.
0.9
0.4
1.00*
100
35–50
20–25
SB-1 (2024), Table 2
Victoria
B.C.
1.1
0.2
1.00*
100
35–50
20–25
NBC 2020, p. C-14
* The formula returns less than 1 kPa (Calgary 0.71, Victoria 0.81, Regina 0.87, Toronto 0.90), so the code's 1 kPa minimum governs.
† Newfoundland and Labrador enforces the 2025 code, which uses 1-in-1,000 values and a different formula. See the next section.
NBC = National Building Code of Canada, Division B, Appendix C, Table C-2. SB-1 = Ontario's Supplementary Standard SB-1, Climatic and Seismic Data. Table compiled October 7, 2026.
What the ranking shows
Four cities sit on the floor. Calgary, Regina, Toronto and Victoria all calculate below 1 kPa and are lifted to it. A house roof in downtown Toronto and one in Calgary are designed to the same minimum, for different reasons: Toronto's ground snow load is low, and Calgary's rain load is almost nil.
The top of the table is Atlantic and Quebec, not the North. Québec City leads at 2.58 kPa, more than two and a half times the minimum. Yellowknife and Whitehorse, with long cold winters and dry snow, land in the bottom half.
Geography inside a region matters as much as the region. Barrie is designed for 1.78 kPa and Toronto for 1.00, roughly an hour's drive apart. Ontario goes further and divides Hamilton into four zones in its Supplementary Standard SB-1: the ground snow load is 1.1 kPa below the escarpment but 1.3 or 1.5 kPa above it, depending on which side of the airport the property sits. That moves the specified roof load on the Mountain to between 1.12 and 1.23 kPa.
The figures also carry a stated margin of error. The code notes that although ground snow loads are listed to a tenth of a kilopascal, they typically have an uncertainty of about 20%, and it warns against interpolating between listed locations. Treat the table as a reference for scale, then ask your municipal building department what applies at your address.
The table ranks 30 cities from the highest specified roof snow load to the lowest. Every S<sub>s</sub> and S<sub>r</sub> value was read from the code document named in the last column, not from a secondary website. Depths are rounded to the nearest 5 cm and are approximate by nature.
30 rows · 9 columnsTap a header to sort
Québec City
Que.
3.6
0.6
2.58
260
85–130
50–65
NBC 2020, p. C-30
Corner Brook
N.L.
5.3†
0.9†
2.54
255
85–125
50–65
NBC 2025, p. C-42
St. John's
N.L.
4.4†
1.1†
2.35
235
80–120
45–60
NBC 2025, p. C-42
Fredericton
N.B.
3.1
0.6
2.31
230
75–115
45–60
NBC 2020, p. C-33
Moncton
N.B.
3.0
0.6
2.25
225
75–110
45–55
NBC 2020, p. C-33
Charlottetown
P.E.I.
2.7
0.6
2.09
210
70–105
40–50
NBC 2020, p. C-34
Prince George
B.C.
3.4
0.2
2.07
205
70–105
40–50
NBC 2020, p. C-13
Thunder Bay
Ont.
2.9
0.4
2.00
200
65–100
40–50
SB-1 (2024), Table 2
Saguenay
Que.
2.7
0.4
1.89
190
65–95
40–45
NBC 2020, p. C-31
Saint John
N.B.
2.3
0.6
1.87
185
60–95
35–45
NBC 2020, p. C-33
Montréal (City Hall)
Que.
2.6
0.4
1.83
185
60–90
35–45
NBC 2020, p. C-30
Sherbrooke
Que.
2.2
0.6
1.81
180
60–90
35–45
NBC 2020, p. C-32
Iqaluit
Nvt.
2.9
0.2
1.80
180
60–90
35–45
NBC 2015, Table C-2
Barrie
Ont.
2.5
0.4
1.78
180
60–90
35–45
SB-1 (2024), Table 2
Sudbury
Ont.
2.5
0.4
1.78
180
60–90
35–45
SB-1 (2024), Table 2
Ottawa (City Hall)
Ont.
2.4
0.4
1.72
170
55–85
35–45
SB-1 (2024), Table 2
Halifax
N.S.
1.9
0.6
1.65
165
55–80
35–40
NBC 2020, p. C-33
London
Ont.
1.9
0.4
1.45
145
50–70
30–35
SB-1 (2024), Table 2
Yellowknife
N.W.T.
2.2
0.1
1.31
130
45–65
25–35
NBC 2020, p. C-36
Winnipeg
Man.
1.9
0.2
1.25
125
40–60
25–30
NBC 2020, p. C-19
Whitehorse
Y.T.
2.0
0.1
1.20
120
40–60
25–30
NBC 2020, p. C-35
Vancouver (City Hall)
B.C.
1.8
0.2
1.19
120
40–60
25–30
NBC 2020, p. C-14
Edmonton
Alta.
1.7
0.1
1.04
105
35–50
20–25
NBC 2020, p. C-15
Kelowna
B.C.
1.7
0.1
1.04
105
35–50
20–25
NBC 2020, p. C-12
Saskatoon
Sask.
1.7
0.1
1.04
105
35–50
20–25
NBC 2020, p. C-18
Hamilton (below the escarpment)
Ont.
1.1
0.4
1.01
100
35–50
20–25
SB-1 (2024), Table 2
Calgary
Alta.
1.1
0.1
1.00*
100
35–50
20–25
NBC 2020, p. C-15
Regina
Sask.
1.4
0.1
1.00*
100
35–50
20–25
NBC 2020, p. C-18
Toronto (City Hall)
Ont.
0.9
0.4
1.00*
100
35–50
20–25
SB-1 (2024), Table 2
Victoria
B.C.
1.1
0.2
1.00*
100
35–50
20–25
NBC 2020, p. C-14
* The formula returns less than 1 kPa (Calgary 0.71, Victoria 0.81, Regina 0.87, Toronto 0.90), so the code's 1 kPa minimum governs.
† Newfoundland and Labrador enforces the 2025 code, which uses 1-in-1,000 values and a different formula. See the next section.
NBC = National Building Code of Canada, Division B, Appendix C, Table C-2. SB-1 = Ontario's Supplementary Standard SB-1, Climatic and Seismic Data. Table compiled October 7, 2026.
What the ranking shows
Four cities sit on the floor. Calgary, Regina, Toronto and Victoria all calculate below 1 kPa and are lifted to it. A house roof in downtown Toronto and one in Calgary are designed to the same minimum, for different reasons: Toronto's ground snow load is low, and Calgary's rain load is almost nil.
The top of the table is Atlantic and Quebec, not the North. Québec City leads at 2.58 kPa, more than two and a half times the minimum. Yellowknife and Whitehorse, with long cold winters and dry snow, land in the bottom half.
Geography inside a region matters as much as the region. Barrie is designed for 1.78 kPa and Toronto for 1.00, roughly an hour's drive apart. Ontario goes further and divides Hamilton into four zones in its Supplementary Standard SB-1: the ground snow load is 1.1 kPa below the escarpment but 1.3 or 1.5 kPa above it, depending on which side of the airport the property sits. That moves the specified roof load on the Mountain to between 1.12 and 1.23 kPa.
The figures also carry a stated margin of error. The code notes that although ground snow loads are listed to a tenth of a kilopascal, they typically have an uncertainty of about 20%, and it warns against interpolating between listed locations. Treat the table as a reference for scale, then ask your municipal building department what applies at your address.
Building codes are provincial and territorial law. The national code is a model that each jurisdiction adopts, sometimes with changes, on its own schedule. According to the adoption tracker kept by the Canadian Board for Harmonized Construction Codes, the 2020 edition is now the basis nearly everywhere: British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, Prince Edward Island, Yukon and the Northwest Territories.
There are two exceptions, and they point in opposite directions. Nunavut still enforces the 2015 edition. That does not change Iqaluit's row, because the 2015 table lists the same 2.9 and 0.2 kPa. Newfoundland and Labrador moved the other way and began enforcing the 2025 edition on July 12, 2026.
What changed in the 2025 code
The 2025 edition rewrites the house formula. In the National Building Code of Canada 2025, the specified snow load becomes S = (C<sub>b</sub> × S<sub>s</sub> + S<sub>r</sub>) ÷ 1.5, where both snow terms are now 1-in-1,000 annual probability values. The roof factor and the 1 kPa minimum are unchanged. Table C-2 prints the rarer values in new columns beside the familiar 1-in-50 ones.
For St. John's, the 1-in-1,000 figures are 4.4 and 1.1 kPa, which gives 2.35 kPa. Under the 2020 formula the city would have been 2.30. For Corner Brook the new formula gives 2.54 kPa against 2.64 under the old one. The method is different; the results are close, and they do not all move in the same direction.
The climatic data behind the table is changing too. The 2025 code is the first to build projected future conditions into its design values, as the Canadian Centre for Climate Services explains. Where a projected change would raise a design demand, the value is adjusted. Where it would lower one, the historical value stays. Expect the figures in this table to be revisited as other provinces adopt the newer edition.
Do provincial codes publish different numbers?
Mostly not. Ontario, British Columbia, Alberta and Quebec each publish their own code documents, and we opened all four. British Columbia's 2024 code adopts the national document as its first book and lists the same values for Kelowna, Prince George and Victoria. Alberta's 2023 edition matches for Calgary and Edmonton, and Quebec's amended code matches for all four Quebec cities. Hamilton is the only place in the table where a provincial figure departs from the national one.
One caution on Vancouver: the city enforces its own building by-law, separate from the provincial code. The row above uses the national table's City Hall value.
Building codes are provincial and territorial law. The national code is a model that each jurisdiction adopts, sometimes with changes, on its own schedule. According to the adoption tracker kept by the Canadian Board for Harmonized Construction Codes, the 2020 edition is now the basis nearly everywhere: British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, Prince Edward Island, Yukon and the Northwest Territories.
There are two exceptions, and they point in opposite directions. Nunavut still enforces the 2015 edition. That does not change Iqaluit's row, because the 2015 table lists the same 2.9 and 0.2 kPa. Newfoundland and Labrador moved the other way and began enforcing the 2025 edition on July 12, 2026.
What changed in the 2025 code
The 2025 edition rewrites the house formula. In the National Building Code of Canada 2025, the specified snow load becomes S = (C<sub>b</sub> × S<sub>s</sub> + S<sub>r</sub>) ÷ 1.5, where both snow terms are now 1-in-1,000 annual probability values. The roof factor and the 1 kPa minimum are unchanged. Table C-2 prints the rarer values in new columns beside the familiar 1-in-50 ones.
For St. John's, the 1-in-1,000 figures are 4.4 and 1.1 kPa, which gives 2.35 kPa. Under the 2020 formula the city would have been 2.30. For Corner Brook the new formula gives 2.54 kPa against 2.64 under the old one. The method is different; the results are close, and they do not all move in the same direction.
The climatic data behind the table is changing too. The 2025 code is the first to build projected future conditions into its design values, as the Canadian Centre for Climate Services explains. Where a projected change would raise a design demand, the value is adjusted. Where it would lower one, the historical value stays. Expect the figures in this table to be revisited as other provinces adopt the newer edition.
Do provincial codes publish different numbers?
Mostly not. Ontario, British Columbia, Alberta and Quebec each publish their own code documents, and we opened all four. British Columbia's 2024 code adopts the national document as its first book and lists the same values for Kelowna, Prince George and Victoria. Alberta's 2023 edition matches for Calgary and Edmonton, and Quebec's amended code matches for all four Quebec cities. Hamilton is the only place in the table where a provincial figure departs from the national one.
One caution on Vancouver: the city enforces its own building by-law, separate from the provincial code. The row above uses the national table's City Hall value.
Why depth alone misleads
Density is the first reason. A roof holding 50 cm of new powder at 1 kN/m³ is carrying about 0.5 kPa. The same 50 cm of old, wet snow at 4 kN/m³ is carrying 2.0 kPa, which is the full design figure for Thunder Bay. Nothing about the depth changed.
Rain is the second. The code's own commentary in Appendix C states that the heaviest loads frequently occur when the snow is wetted by rain, which is why a rain load is added to every calculation. That single term reshuffles the ranking. Halifax and Winnipeg share a ground snow load of 1.9 kPa. Halifax's rain load is 0.6 and Winnipeg's is 0.2, so Halifax's roof figure is 1.65 kPa and Winnipeg's is 1.25.
Quebec's building regulator has made the same point in plainer words. After a stretch of snow followed by rain and freezing rain in January 2018, a spokesperson for the Régie du bâtiment told CBC News that "not all snow is created equal", while adding that roofs are built to resist the weather and that there was no cause for alarm.
Drifts are deeper and denser
Wind does not spread snow evenly. It scours open roof planes and piles snow wherever a roof meets a higher wall: below a second storey, beside a dormer, in a valley. Those drifts are heavier per centimetre as well as deeper. Field measurements by the National Research Council on more than 40 flat-roofed buildings between Halifax and Edmonton found that snow in drifts at changes in roof elevation averaged a specific gravity of about 0.3, some 25% higher than the design value of the day.
The practical reading: the depth you can see on the main roof from the street says little about the load in the corner where a garage roof meets the house wall.
Density is the first reason. A roof holding 50 cm of new powder at 1 kN/m³ is carrying about 0.5 kPa. The same 50 cm of old, wet snow at 4 kN/m³ is carrying 2.0 kPa, which is the full design figure for Thunder Bay. Nothing about the depth changed.
Rain is the second. The code's own commentary in Appendix C states that the heaviest loads frequently occur when the snow is wetted by rain, which is why a rain load is added to every calculation. That single term reshuffles the ranking. Halifax and Winnipeg share a ground snow load of 1.9 kPa. Halifax's rain load is 0.6 and Winnipeg's is 0.2, so Halifax's roof figure is 1.65 kPa and Winnipeg's is 1.25.
Quebec's building regulator has made the same point in plainer words. After a stretch of snow followed by rain and freezing rain in January 2018, a spokesperson for the Régie du bâtiment told CBC News that "not all snow is created equal", while adding that roofs are built to resist the weather and that there was no cause for alarm.
Drifts are deeper and denser
Wind does not spread snow evenly. It scours open roof planes and piles snow wherever a roof meets a higher wall: below a second storey, beside a dormer, in a valley. Those drifts are heavier per centimetre as well as deeper. Field measurements by the National Research Council on more than 40 flat-roofed buildings between Halifax and Edmonton found that snow in drifts at changes in roof elevation averaged a specific gravity of about 0.3, some 25% higher than the design value of the day.
The practical reading: the depth you can see on the main roof from the street says little about the load in the corner where a garage roof meets the house wall.
The simplified formula was written for a specific kind of building: light wood framing with closely spaced, repetitive members and modest spans. The code's explanatory note describes it as suited to traditional wood-frame residential construction and says it assumes considerable redundancy in the structure. Step outside that description and the table stops being a guide.
Flat and low-slope roofs. The simplified load does not apply where parapets or other large projections trap snow on a flat roof. Flat roofs also hold meltwater and rain if drains freeze over.
Lower roofs beside taller walls. The code treats drift zones separately. For one configuration it requires the lower roof to carry not less than 1.5 times the specified load near the step.
Sheds, carports and awnings. The National Research Council notes that the same requirements may not apply to small accessory buildings and suggests monitoring them and raking them from the ground more regularly.
Temporary car shelters. These are not designed like a roof at all. Quebec's regulator says to keep them free of build-up and, in its snow and ice removal guidance, never to clear one while standing inside it.
Altered houses. The same guidance says an engineer's review is especially important if the building has undergone major modifications. Removed walls, added dormers and new rooftop equipment all change how load travels to the foundation.
Older houses. Design methods and materials have changed over the decades. The National Research Council's view is measured: an older roof is not a cause for concern on age alone, since it has demonstrated its performance over many winters. Its past performance still says nothing about a snow load heavier than any it has seen.
Signs a roof is under stress, and the next step for each
A roof that is carrying more than it should often shows it indoors first. The framing deflects, and the finishes attached to it show the movement. The Régie du bâtiment du Québec publishes a short list of signs, and the National Research Council's frequently asked questions on snow loads adds a few more. Together they make a workable triage.
Interior doors that start to jam or rub. A door that closed freely last week and now sticks on an upper floor is the earliest common sign. Note which doors, then check the rest of the list.
New cracks in drywall or plaster. Look at ceiling-to-wall joints and above door frames on the top floor. Photograph them with a date so you can tell whether they grow.
Creaking, cracking or popping from above. Houses make noise in cold weather. Sounds that are new, repeated and come from the roof or the walls that hold it up belong on this list.
A ceiling that sags, bows or buckles. Treat visible deformation as serious. Move people out of the rooms below it.
Water leaks that appear after a heavy snowfall. A leak can be an ice dam or a flashing failure. Alongside any other sign here, it points to structure.
One sign on its own is a reason to watch closely and call for an assessment. Quebec's regulator is direct about what several at once mean: if such signs are numerous, evacuate the building and arrange to have the snow load removed.
Important
If a ceiling is visibly deforming or you hear repeated cracking from the roof structure, leave the house first and make calls from outside. Do not go up to look, and do not go into the attic.
The person to call is a structural engineer. The National Research Council also suggests a local building-science specialist, typically an architect or consulting engineer, and your municipal building department can tell you which requirements your house was built to.
Leaks that show up without any of the structural signs are a different diagnosis, and the guide to roof leaks walks through tracing them.
When clearing is worth the risk, and when it is not
Start from the design assumption. A code-built roof is meant to carry its snow load without anyone removing it. The National Building Code says so in as many words for engineered buildings: snow removal by mechanical, thermal, manual or other means shall not be used as a rationale to reduce design snow loads. Clearing is an exception for unusual winters, not routine maintenance.
What official guidance says about depth
We looked for a published depth trigger from a Canadian authority and found exactly one. Saskatchewan's Building Standards Advisory on snow loads on roofs says building owners should be concerned any time snow is more than two feet deep over the whole roof, or when the load is unevenly distributed. It immediately adds that the depth is a guideline only. The advisory dates from October 2015.
Quebec's regulator, the National Research Council and the Insurance Bureau of Canada publish no depth figure at all. That absence is informative. Two feet, about 60 cm, of settled snow weighs somewhere between 1.2 and 1.8 kPa depending on its density. No single depth can be right for both Regina and Québec City, or for powder and slush.
The default is to leave it
For a sloped house roof showing no signs of stress, in an ordinary winter, the evidence favours leaving the snow where it is. The National Research Council's advice to homeowners is blunt: you should never clear a roof yourself. It allows one exception, a snow rake used from ground level where the roof can be reached that way, and even then with care.
Workplace safety rules treat the roof itself as the last option for trained crews. Quebec's safety board, the CNESST, sets out a hierarchy for clearing a roof that begins with working from the ground, moves to a lifting platform with guardrails, and permits working on a sloped roof only as a last resort. It notes that a telescopic roof rake is very often enough for a house.
The stakes of a short fall are not hypothetical. A CNESST investigation found that a snow-removal worker in Témiscouata-sur-le-Lac died in March 2025 after falling 3.96 metres from a ladder while clearing snow from truck trailers. That was a trailer, not a house, and a paid worker, not a homeowner. The height is about that of a bungalow eave. We found no Canadian statistics on homeowner injuries from roof clearing, so we will not suggest a rate.
When clearing makes sense
Removal becomes reasonable when the conditions Quebec's regulator calls exceptional or atypical line up: a deep existing snowpack with rain or freezing rain forecast on top of it, heavy drifting against a higher wall, a flat roof with blocked drains, or any of the indoor signs above. In those cases the question is who does it and how.
Hire for anything that cannot be reached from the ground. The Insurance Bureau of Canada's winter checklist frames it as clearing the roof and deck or hiring a professional to do it. In Quebec no licence is required for roof snow removal, so ask about experience, fall-protection equipment and liability insurance.
Rake from the ground, standing clear. Stay out of the zone where snow and ice will land, and well away from the power line that feeds the house.
Leave a thin layer. Quebec's regulator advises leaving a little snow on the surface to protect the roofing. Scraping down to the shingles can damage or tear them.
Do not chip ice. Chopping at ice risks damaging the roof surface and causing leaks. If ice is the problem, the cause is heat loss, not snow.
Keep the ground-level items clear. Exits, gas meters, and furnace, dryer and exhaust vents are the part of snow clearing every household can do safely.
Start from the design assumption. A code-built roof is meant to carry its snow load without anyone removing it. The National Building Code says so in as many words for engineered buildings: snow removal by mechanical, thermal, manual or other means shall not be used as a rationale to reduce design snow loads. Clearing is an exception for unusual winters, not routine maintenance.
What official guidance says about depth
We looked for a published depth trigger from a Canadian authority and found exactly one. Saskatchewan's Building Standards Advisory on snow loads on roofs says building owners should be concerned any time snow is more than two feet deep over the whole roof, or when the load is unevenly distributed. It immediately adds that the depth is a guideline only. The advisory dates from October 2015.
Quebec's regulator, the National Research Council and the Insurance Bureau of Canada publish no depth figure at all. That absence is informative. Two feet, about 60 cm, of settled snow weighs somewhere between 1.2 and 1.8 kPa depending on its density. No single depth can be right for both Regina and Québec City, or for powder and slush.
The default is to leave it
For a sloped house roof showing no signs of stress, in an ordinary winter, the evidence favours leaving the snow where it is. The National Research Council's advice to homeowners is blunt: you should never clear a roof yourself. It allows one exception, a snow rake used from ground level where the roof can be reached that way, and even then with care.
Workplace safety rules treat the roof itself as the last option for trained crews. Quebec's safety board, the CNESST, sets out a hierarchy for clearing a roof that begins with working from the ground, moves to a lifting platform with guardrails, and permits working on a sloped roof only as a last resort. It notes that a telescopic roof rake is very often enough for a house.
The stakes of a short fall are not hypothetical. A CNESST investigation found that a snow-removal worker in Témiscouata-sur-le-Lac died in March 2025 after falling 3.96 metres from a ladder while clearing snow from truck trailers. That was a trailer, not a house, and a paid worker, not a homeowner. The height is about that of a bungalow eave. We found no Canadian statistics on homeowner injuries from roof clearing, so we will not suggest a rate.
When clearing makes sense
Removal becomes reasonable when the conditions Quebec's regulator calls exceptional or atypical line up: a deep existing snowpack with rain or freezing rain forecast on top of it, heavy drifting against a higher wall, a flat roof with blocked drains, or any of the indoor signs above. In those cases the question is who does it and how.
Hire for anything that cannot be reached from the ground. The Insurance Bureau of Canada's winter checklist frames it as clearing the roof and deck or hiring a professional to do it. In Quebec no licence is required for roof snow removal, so ask about experience, fall-protection equipment and liability insurance.
Rake from the ground, standing clear. Stay out of the zone where snow and ice will land, and well away from the power line that feeds the house.
Leave a thin layer. Quebec's regulator advises leaving a little snow on the surface to protect the roofing. Scraping down to the shingles can damage or tear them.
Do not chip ice. Chopping at ice risks damaging the roof surface and causing leaks. If ice is the problem, the cause is heat loss, not snow.
Keep the ground-level items clear. Exits, gas meters, and furnace, dryer and exhaust vents are the part of snow clearing every household can do safely.
Tip
Book a roof-clearing contractor in the fall if you live in the upper half of the table or own a flat-roofed building. Crews are hardest to reach in the week everyone needs one.
Ryan is the founder of Homeowner.ca and a proud Canadian homeowner based in Guelph, Ontario. Over his 25-year career in digital publishing, he has focused on transforming complex information into clear, practical guidance that helps people make confident, well-informed decisions.
No. It is the minimum load the code requires the structure to be designed for. It is not a measured capacity for your roof, and it is not a safe-up-to line either. Workmanship, age, alterations and the condition of the framing all affect what a particular roof can carry, and only an on-site assessment by an engineer can speak to that.
Multiply by 20.9. A 1 kPa load is about 21 psf, Ottawa's 1.72 kPa is about 36 psf, and Québec City's 2.58 kPa is about 54 psf.
Not reliably. The code warns that values should not be interpolated for unlisted locations, because ground snow load shifts with elevation and local terrain. Vancouver City Hall is listed at 1.8 kPa and North Vancouver at 3.0. The national table covers several hundred locations beyond these 30, and your municipal building department can give you the figure it enforces.
Using the code's figures, roughly 100 kg for new snow and 200 to 500 kg for old snow. Snow that has absorbed rain sits at the heavy end of that range.
The simplified house formula has no term for slope or surface. In practice both matter: the National Research Council notes that low-slope roofs and rough roofing materials tend to hold more snow than steep pitches or slippery finishes.
It applies only where the entire width of the roof is 4.3 m or less. That covers narrow roofs such as a small porch, not the main roof of a house.
A deck or balcony serving a single home must be designed for the specified roof snow load or 1.9 kPa, whichever is greater. In most of the cities in the table, that makes the deck's minimum higher than the roof's.
The code does not accept snow removal as a reason to design for less load, and it is not a substitute for structure. If you have reason to think a roof was under-built or weakened by renovation, the fix is an engineer's assessment, not a clearing schedule.
Your municipal building department can tell you which requirements the house was built to. For an opinion on the roof itself, a structural engineer or a building-science consultant can assess it on site.
Yes. The Insurance Bureau of Canada and Saskatchewan's building standards branch both advise keeping gas meters, appliance vents and exhaust vents clear of snow and ice. Blocked vents are a health risk that has nothing to do with roof load.
Sources
Canadian Board for Harmonized Construction Codes. (2026). Provincial/Territorial Adoption. Retrieved from https://cbhcc-cchcc.ca/
Canadian Centre for Climate Services. (2026). New 2025 National Building Code Uses Future Climate Data for First Time. Retrieved from https://climatedata.ca/
Saskatchewan Ministry of Government Relations, Building Standards and Licensing Branch. (2015). Building Standards Advisory: Snow Loads on Roof. Retrieved from https://kindersley.ca/
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National Research Council of Canada. (2024). National Building Code – 2023 Alberta Edition. Retrieved from https://nrc-publications.canada.ca/
Taylor, D. A. (1987). Snow Loads on Multi-Level Flat Roofs in Canada (NRCC 28486). National Research Council Canada. Retrieved from https://nrc-publications.canada.ca/
Canadian Commission on Building and Fire Codes. (2022). National Building Code of Canada 2020. National Research Council of Canada. Retrieved from https://nrc-publications.canada.ca/
Canadian Board for Harmonized Construction Codes. (2025). National Building Code of Canada 2025. National Research Council of Canada. Retrieved from https://nrc-publications.canada.ca/
Canadian Commission on Building and Fire Codes. (2015). National Building Code of Canada 2015. National Research Council of Canada. Retrieved from https://nrc-publications.canada.ca/
National Research Council of Canada & Régie du bâtiment du Québec. (2025). Quebec Construction Code, Chapter I – Building, and National Building Code of Canada 2020 (amended). Retrieved from https://nrc-publications.canada.ca/
National Research Council of Canada. (n.d.). Codes Canada – Frequently Asked Questions: Snow Loads (archived page). Retrieved from https://nrc.canada.ca/
CBC News. (2018). It's Time to Clear the Snow Off Your Roof, Régie du bâtiment Warns. Retrieved from https://www.cbc.ca/
CBC News. (2019). Snow, Ice Buildup Causes Roofs to Collapse in Central Quebec. Retrieved from https://www.cbc.ca/
Commission des normes, de l'équité, de la santé et de la sécurité du travail. (n.d.). Déneiger un toit. Retrieved from https://www.cnesst.gouv.qc.ca/
The Canadian Press. (2025). Death of a Roof Snow Remover Result of Poor Work Methods, Concludes the CNESST. CTV News. Retrieved from https://www.ctvnews.ca/
Insurance Bureau of Canada. (n.d.). Ice and Snow Protection. Retrieved from https://www.ibc.ca/
Ontario Ministry of Municipal Affairs and Housing. (2024). 2024 Building Code Compendium, Volume 2: Supplementary Standard SB-1, Climatic and Seismic Data. Retrieved from https://www.publications.gov.on.ca/
