How much snow must a roof in BC carry, and will an older cabin's roof hold?

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A roof is built for the snow the building code sets for its location, from the ground snow load the building department gives, so an older roof was built for its own day's figure. The snow a roof must carry isn't the average snowfall: it's the code's figure for the heaviest snow on the ground expected once in 50 years at that spot, with the rain that soaks into it. A buyer's questions are what figure the lot's building department uses, what the house was built for, and whether anything heavier has gone on the roof since. Look up the address or PID on PlaceDossier to see the record for that lot. How the load is set: Under Part 9, which covers houses, a roof is designed for at least the 1-in-50-year ground snow load times 0.45 where the whole roof is no more than 4.3 m wide, or 0.55 for any other roof, plus the rain load that comes with it, and never less than 1 kPa (BC Building Code 2024, Division B, Article 9.4.2.2). Larger buildings and long-span trusses are designed under Part 4, which adds factors for the building's importance, wind exposure, roof slope and drifting snow (Article 4.1.6.2). Where the lot's figure comes from: The ground snow and rain loads are the values the authority having jurisdiction sets, and where it sets none, those in the Code's Appendix C (Division B, Sentence 1.1.3.1 (1), (2)). Many councils publish their own table by elevation, and the building department gives the figure for a permit. In the mountains: Appendix C lists over 100 places. Its notes say its values apply to populated valleys, not mountain slopes and passes, that they shouldn't be interpolated for unlisted places in complex terrain, and that Environment and Climate Change Canada gives values for places not listed; snow loads above a valley's reference level rise with elevation. So a cabin well above the valley floor can need a much higher figure than the town below (our reading of those notes). Decks and balconies: A deck, balcony or other outdoor platform serving one home is designed to carry the roof snow load or 1.9 kPa, whichever is greater (Article 9.4.2.3). An older building: A house is designed to the code in force when its permit was taken, and the national code's ground snow loads were last updated for its 2015 edition (Appendix C's notes), so an older roof's capacity can't be read from today's figure (our reading). Before adding a heavier roof covering, solar panels, a new roof over the old one or a room in the attic, have an engineer or the building department check the framing. Sheds, carports and barns: Whether a small shed or carport needs a permit is the council's building bylaw (see building permits and sheds and garages); a barn is designed to the farm building code (see barns and farm buildings). Ask the building department what an outbuilding must carry before you build or buy one for winter use (our reading). Clearing a roof: Clearing snow is work at a height: an employer must use fall protection where a worker could fall 3 m or more (WorkSafeBC's Occupational Health and Safety Regulation s. 11.2), so ask anyone you hire how they'll do it. Shovelling unevenly can load one side of a roof more than the other (our reading). What it means for a buyer: Ask whether the roof has sagged, leaked at the eaves or been cleared in a heavy winter, whether anything was added to it, and for the permit drawings, which can show the design load. On land to build on up a mountain road, ask the building department the snow load at that elevation before you buy: it shapes the roof and what the house costs to build.

How much snow must a roof in BC carry, and will an older cabin's roof hold?

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Before you buy: who to ask