Roof Snow Load Requirements

The standard practice for a few decades in new hampshire was to build our roofs to support 40 pounds per square foot psf live snow load.

Roof snow load requirements.

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. Schilke civil agricultural engineering montana state university august 1989. 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.

The final roof design loads shall not be less than 20 psf after all reductions are factored except for lyon storey counties. Ground snow loads p g for northern nevada locations 1. A clay tiled roof may have a dead load. The flat roof snow load is calculated using formula 7 3 1.

Table r301 2 1 climatic and geographic design criteria ground snow load. The dead load of a typical asphalt shingled wood framed roof is about 15 pounds per square foot. 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. In our case let s assume that our structure has a flat roof roof slope 5.

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. Unfortunately most buildings constructed during those years 1970 2000 do not even meet the 40 psf requirement. Intermediate values may be interpolated by proportion. 1603 1 3 roof snow load data the ground snow load pg shall be indicated.

Flat roof snow load pf. The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load. The residential code of ohio which applies to one and two family homes shows a map indicating the required snow load. The 20 psf load is equivalent to 14 inches of snow at the design density while the 25 psf load is 17 inches.

Why snow load information. That s about 4 feet of powder and as little as 2 feet of wet snow. The north zone middle zone and the south zone are identified on the roof load zone map above. Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10.

This downward imposed load on the home is also known as the snow load. The minimum design roof snow load after allowed reductions shall be 30 psf.