Snow Load Flat Roof Design

If your structure has a sloped or flat roof you still need to calculate the flat roof snow load.

Snow load flat roof design.

In these situations make sure to act quickly any delay may be potentially dangerous for both the structure and the residents. Step 4 determine the flat roof snow load. Load types loads used in design load equations are given letters by type. The thermal factor c t from table e 3 determines if a roof is cold or warm slippery surface values shall be used only where the roof s surface is unobstructed and sufficient space is available below.

In colder regions the design snow load represents snow deposited by multiple snow events. In between snow events roofs may lose snow mass due to either wind scour or by melting from building heat loss. Snow loads acting on a sloping surface shall be assumed to act on the horizontal projection of that surface. Flat roofs must be installed on a very specific mild slope so that the water can drain off properly and if the drains and scuppers aren t cleared regularly this increases the chance of a leak.

Per asce 7 05 section 7 10. D dead load l live load l r live roof load w wind load s snow load e earthquake load r rainwater load or ice water load t effect of material temperature h hydraulic loads from soil f hydraulic loads from fluids. 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. A flat roof is no more or less likely to leak than a pitched roof it all comes down to the design and the competence with which it is installed.

Flat roof snow loads of 30 psf 1 44 kn m 2 or less and roof live loads of 30 psf 1 44 kn m 2 or less need not be combined with seismic loads. This is the snow load calculated in the previous section. This may also be true in some more moderate climates as well. The sloped roof snow load p s shall be obtained by multiplying the flat roof snow load p f by the roof slope factor c s.

P s c s p f. Where flat roof snow loads exceed 30 psf 1 44 kn m 2 20 percent shall be combined with seismic loads. 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. The design snow load represents the peak snow accumulation on a roof over the a winter season.

The balanced snow load is applied everywhere where the roof structure is located. After you obtain the roof slope factor from those sections in asce 7 10 the balanced design snow load for the sloped roof can easily be calculated using equation 7 4 1. 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. 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.

This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads. Used but they typically defined the load cases or combination stress or strength limits and deflection limits.