Snow Load Flat Roof Design

Used but they typically defined the load cases or combination stress or strength limits and deflection limits.

Snow load flat roof design.

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. 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. 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. 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.

Step 4 determine the flat roof snow load. This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads. Regardless of the recommendations of this snow load calculator there are some cases in which you should always remove the snow from your roof. The design snow load represents the peak snow accumulation on a roof over the a winter season.

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. P s c s p f. 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.

Per asce 7 05 section 7 10. Snow loads acting on a sloping surface shall be assumed to act on the horizontal projection of that surface. 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. Determine the transient load of the roof.

Where flat roof snow loads exceed 30 psf 1 44 kn m 2 20 percent shall be combined with seismic loads. This is the snow load calculated in the previous section. 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. 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 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. In between snow events roofs may lose snow mass due to either wind scour or by melting from building heat loss. The balanced snow load is applied everywhere where the roof structure is located. In colder regions the design snow load represents snow deposited by multiple snow events.

This may also be true in some more moderate climates as well. 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.