Flat Roof Snow Load

If your roof is flat it is more likely to have snow load problems than if it is pitched.

Flat roof snow load.

Snow load thickness density. Pg is converted to pf by this formula. Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10. The design snow load represents the peak snow accumulation on a roof over the a winter season.

This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads. Flat roof snow loads p f the snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load. You can also find the load per square meter or square foot of roofing by opening the advanced mode. First figure out how deep the snow is piled up there.

Flat roof snow load are determined by the following method. The snow load pf on a roof with a slope equal to or less than 5 degrees 1 in ft 4 76 deg shall be calculated in lb ft2 kn m2 using the following formula. Wind loads depend on wind speed and can vary as widely as the snow. Step 4 determine the flat roof snow load.

For ground snow loads greater than 20 pounds per square foot the roof load is equal to 70 of the product of the exposure thermal and importance factors the ground snow load and 20 pounds. Often changes of five or 10 pounds per square foot result in minimal differences in cost. This rain on snow augmented design load applies only to the balanced load case and need not be used in combination with drift sliding unbalanced or partial loads. In colder regions the design snow load represents snow deposited by multiple snow events.

Once you know these values our snow load calculator automatically finds the total weight of snow on your roof. The flat roof snow load ρ f on a roof with a slope equal to or less than 5 degrees 0 09 rad 1 inch per foot 4 76 degrees shall be calculated in accordance with section 7 3 of asce 7. This is highly regional as weights of snow for example range from 10 to 300 pounds per square foot based on moisture and volume of the snow. 0 7 x ce x ct x is x pg pf.

In our case let s assume that our structure has a flat roof roof slope 5. This may also be true in some more moderate climates as well. If you want to calculate these values by hand use the following formulas. Once you have the ground snow load p g you can compute the flat roof snow load p f.

For roofs that are flat and with ground snow loads lower than 20 pounds per square foot the roof snow load is equal to 70 of the product of the exposure thermal and importance factors and the ground snow load. For locations where 0 pg 20 psf all roofs with a slope w 50 with w in ft shall have a 5 psf rain on snow surcharge.