Request a Free QuoteNiagara Region, Ontario · LANE: NIAGARA SNOW LOAD GUIDE
Fence and Deck Building & Repair Experts
Snow load is one of the reasons two quotes for the same covered deck or shed in two Niagara towns can differ. A roof has to be framed for the snow its town is expected to get, and a heavier load means shorter spans between supports, or bigger lumber, or both. The Building Code's own roof-joist span table (Table 9.23.4.2.-D) shows how much. A No. 1 or No. 2 spruce-pine-fir 2x6 (38 x 140 mm) roof joist at 400 mm (16 in.) spacing may span 3.53 m at a 1.0 kPa snow load, 3.08 m at 1.5 kPa, and 2.80 m at 2.0 kPa. We are not putting a dollar figure on that difference, because it depends on the size and shape of the roof. When you ask for an estimate on anything with a roof, it is fair to ask which snow load it was framed for.
Ontario's Building Code does not leave snow to guesswork. Article 9.4.1.1.(3) says snow loads are taken from the province's climate table, Supplementary Standard SB-1, and SB-1 lists a 1-in-50-year ground snow load (Ss) and rain load (Sr) for named places. These are the Niagara rows in the current table, ground snow first: Grimsby 0.9 kPa (about 19 psf), St. Catharines 1.0 kPa (21 psf), Smithville 1.5 kPa (31 psf), Niagara Falls 1.8 kPa (38 psf), Welland 2.0 kPa (42 psf), Pelham (Fonthill) 2.1 kPa (44 psf), Port Colborne 2.1 kPa (44 psf), and Fort Erie and Ridgeway 2.3 kPa (48 psf). The rain load is 0.4 kPa in every one of them. Fort Erie's ground figure is more than twice St. Catharines'. The two Lake Ontario towns in the table sit lowest. Niagara-on-the-Lake, Thorold and Lincoln are not in the table. SB-1 says values for places not listed can be requested from Environment and Climate Change Canada, and that they "may differ from the values accepted by municipal building authorities based on local experience." We have not guessed a number for those towns. Ask the building department which value it uses. The ground figure is not the number a roof is built to. Article 9.4.2.2 turns it into a roof load with S = Cb x Ss + Sr, where Cb is 0.45 when the entire width of the roof is 4.3 m or less and 0.55 for every other roof, and the result can never be less than 1 kPa. Running that formula is our arithmetic, not a town ruling. For a roof up to 4.3 m wide it comes out at 1.0 kPa in Grimsby and St. Catharines (the 1 kPa floor), about 1.08 in Smithville, 1.21 in Niagara Falls, 1.30 in Welland, 1.35 in Pelham and Port Colborne, and 1.44 in Fort Erie. For a wider roof it is 1.0, 1.0, 1.23, 1.39, 1.50, 1.56 and 1.67 kPa in the same order. Decks have their own rule. Article 9.4.2.3 says a deck or balcony serving one home "shall be designed to carry the specified roof snow load or 1.9 kPa, whichever is greater." The highest roof figure above is 1.67 kPa, in Fort Erie, so in every Niagara town in the table the 1.9 kPa (about 40 psf) floor is the number a deck is built to. Roofs are where the towns differ. A solid roof over a pergola or a deck brings it back into building-permit review, and the town's snow load is part of what that review checks. See /pergola-permit-guide/ and /niagara-deck-permit-guide/ for when a permit is needed.
Here is what that means for the things in your yard this winter. A deck with nothing over it: the 1.9 kPa design floor is higher than the Code's roof snow load in every listed Niagara town. For what to check on an older deck, see /niagara-deck-inspection-guide/ and /deck-repair/. An open pergola with slats or rafters and no cover: we found no Code rule that sets a snow load for an open slatted top, so we are not stating one. A pergola, porch or deck with a solid roof: this is where the town matters. A roof framed for St. Catharines' 1.0 kPa is framed for less snow than the same roof in Welland (1.30 to 1.50) or Fort Erie (1.44 to 1.67). If a solid roof went on without a permit, nobody has checked it against those numbers. If it sags between supports or a connection has cracked, deal with it before the snow, not after. A shed or garage roof: the same formula applies. A roof up to 4.3 m wide takes the 0.45 factor, and a wider one takes 0.55 and the higher number. Peter builds decks, pergolas, covered porches, sheds and garages across Niagara, and repairs decks. If you are planning a covered structure for spring, use the contact details below and tell him which town you are in.
Under the Ontario Building Code, Article 9.4.2.3, a deck serving one home is designed for the roof snow load or 1.9 kPa (about 40 psf), whichever is greater. In every Niagara town listed in the Code's climate table the roof snow load is lower than 1.9 kPa, so 1.9 kPa is the figure.
Supplementary Standard SB-1 lists a 1-in-50-year ground snow load of 1.0 kPa for St. Catharines, 1.8 kPa for Niagara Falls and 2.0 kPa for Welland, each with a 0.4 kPa rain load. Fort Erie is the highest in the region at 2.3 kPa and Grimsby the lowest at 0.9 kPa.
The table gives the values, not the reasons. SB-1 says that, where possible, its values were adjusted for elevation and known topographical effects. Fort Erie and Port Colborne sit on Lake Erie while St. Catharines and Grimsby are on Lake Ontario. Whatever the cause, the Code value for Fort Erie is 2.3 kPa and for St. Catharines 1.0 kPa.
Neither is listed in SB-1. The standard says values for unlisted places can be requested from Environment and Climate Change Canada, and that a municipal building department may accept different values based on local experience. Ask the town's building department which figure it checks permits against.
A pergola with a solid roof does. It goes back into building-permit review, and the roof is checked against the town's snow load under Article 9.4.2.2. We found no Code snow-load rule for an open slatted top.
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