Snow Load On Roof Trusses

The truss could be designed based on the assumption that the 25 psf roof snow load is a factored ground snow load in which case a ground snow load is back calculated using asce 7 based on the specified roof snow load pg 25 psf therein lies the problem with specifying only a roof snow load.

Snow load on roof trusses.

These factors account for variables such as site exposure building importance roof slope and the thermal properties of the roof. Live loads include wind precipitation foot traffic and all other weight that comes and goes. Actual load due to snow will depend upon the shape of the roof and its capacity to retain the snow and each case shall be treated on its own merits. Duration of load dol for snow is typically 1 15.

A live load is a temporary load that puts stress on the structure. Dol can play a part in some snow areas where the building official bo has made the determination snow will remain upon the roof for extended time periods. The information provided here is not intended to replace truss drawings. Lengthand widthof your roof.

The snow load calculations provided by this online tool are for educational and illustrative purposes only. If the snow weighs 10 pounds per cubic foot and there are 1 5 feet on the roof each square foot of the roof is getting 15 pounds of pressure. Snow loads are influenced by elevation general weather and moisture patterns slope direction exposure roof or trail bridge configuration and wind direction and severity. Trusses are designed to carry two types of loads.

To calculate the weight of snow on a roof use the first two sections of our snow load calculator. Engineered truss drawings should be obtained for specific site locations incorporating specific snow load wind speed eave wall height building length and importance factor use of building. The current snow load criteria irc 2012 2015 r301 2 3 irc 2012 2015 figure r301 2 5 ibc 2012 2015 1608 begins with a base value i e. To figure out the load on your roof take the depth of snow in feet and multiply it by the weight of a cubic foot of snow.

A dead load is carried constantly by the truss. The top chord live load tcll of any roof trusses will be the greater of pr or lr. Overestimation of snow loads can unnecessarily increase the cost of construction. If your roof is 1 000 square feet the total snow load is 15 000 pounds of snow.

If a roof is subjected to snow load it should be designed for the actual loads due to snow or for the live loads specified above whichever is more severe. Live loads and dead loads. Ground snow load to which several modification factors are applied. You need to supply the following information.