Roof Rafter Snow

You can use either 2 6 or 2 4 rafters for roofs with a 3 12 pitch or greater but it depends on the overall size of your shed.

Roof rafter snow.

According to the american wood council the maximum span for rafters is about 30 feet and that s with a relatively low load of 20lbs per square foot. Depending on your region you may need to design for a maximum snow load of anything between zero to 65 pounds per square foot or roughly 0 3 kpa. Less snow will accumulate on a slippery roof it will slide off instead. Let s look at the sample table below which shows maximum rafter spans for a snow load of 31 3 pounds per square foot psf.

Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. If your roof is located in windswept areas or even north of the treeline the wind will cause snow drifting making less of it accumulate on your roof. For roofs that won t experience heavy snow loads a gable roof can span up to 22 with 2 4 rafters. Snow increases the overall weight of your roof adding to the forces acting on your rafters.

The roof deck collects the snow load and transfers the weight to the rafters. Slipperiness of the roof. If you have a stick frame roof there are a few basic techniques that you can use to strengthen your rafters. If the snow weighs 10 pounds per cubic foot and there are 1 5 feet on the roof each square foot of the roof is getting 15 pounds of pressure.

It extends outward in both. Strengthening existing roof rafters is a difficult process that often requires professional help. To figure out the load on your roof take the depth of snow in feet and multiply it by the weight of a cubic foot of snow. The truss could be designed based on the assumption that the 25 psf roof snow load is a factored ground snow load in which case a ground snow load is back calculated using asce 7 based on the specified roof snow load pg 25 psf therein lies the problem with specifying only a roof snow load.

If your roof is 1 000 square feet the total snow load is 15 000 pounds of snow. For any rafter the portion of the roof deck that transfers this load is the tributary area. As the load goes up for snow in northern climates or for heavy roofing material like tile the span length decreases.