Roof Snow Load Requirements

Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10.

Roof snow load requirements.

That s about 4 feet of powder and as little as 2 feet of wet snow. The flat roof snow load is calculated using formula 7 3 1. Once the ground snow load at the building site is determined it must then be converted to roof snow loads according to asce 7 with appropriate treatment of exposure to wind thermal properties of the roof roof slope unbalanced snow loads drifting and risk exposure. A great deal of confusion currently exists among engineers architects recreation specialists and maintenance personnel concerning the proper snow loading to use for the design and maintenance of trail bridges building roofs and other structures in mountainous high snow load areas.

Drift load design in the 30 psf zones may utilize asce 7 16 table c7 1 ground snow values. Why snow load information. 1603 1 3 roof snow load data the ground snow load pg shall be indicated. The north zone design live load equates to 40 pounds per square foot the middle zone equates to 30 pounds per square foot and the south zone equates to 20 pounds per square foot.

Intermediate values may be interpolated by proportion. The 20 psf load is equivalent to 14 inches of snow at the design density while the 25 psf load is 17 inches. The load increases with the use of heavier roofing material. Unfortunately most buildings constructed during those years 1970 2000 do not even meet the 40 psf requirement.

Table r301 2 1 climatic and geographic design criteria ground snow load. Flat roof snow load pf. Schilke civil agricultural engineering montana state university august 1989. The minimum design roof snow load after allowed reductions shall be 30 psf.

The north zone middle zone and the south zone are identified on the roof load zone map above. This downward imposed load on the home is also known as the snow load. In our case let s assume that our structure has a flat roof roof slope 5. In areas of the state outside of certified local government jurisdictions the design snow load shall be based on the ground snow loads developed in snow loads for structural design in montana authored by f 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. It calls for 20 psf throughout most of ohio and 25 psf along a north south strip in the eastern half of the state. Ground snow loads p g for northern nevada locations 1. The dead load of a typical asphalt shingled wood framed roof is about 15 pounds per square foot.

In areas where the ground snow load pg exceeds 10 pounds per square foot psf 0 479 kn m 2 the following additional information shall also be provided regardless of whether snow loads govern the design of the roof. The residential code of ohio which applies to one and two family homes shows a map indicating the required snow load.