Figuring Roof Load

This sizing guide for roof rafters will help determine what you need for your small project.

Figuring roof load.

Thus as the roof gets steeper the rafter gets longer and the weight of roofing materials increases. However if the attic is intended for storage the attic live load or some portion should also be considered for the design of. There are several variables to consider when determining the proper rafter size. Explore a number of housing related calculators as well as hundreds of other calculators covering topics such as finance math health fitness and more.

Roofs are under a lot of pressure. Unlike the trussed roof live load and dead load of the rafters and ceiling joists must be accounted for as separate systems. This free roofing calculator estimates the area of a roof and the amount of materials required to replace or build said roof. In order to stay intact and in place a roof must be able to resist loads both permanent and temporary that are pushing.

The load on your roof trusses can be calculated based on the number of members and the number of nodes in the structure. If you live in the us our snow load calculator compares the total weight on your roof with the permissible load calculated according to the standards issued by the american society of civil engineers regarding the minimum design loads for buildings and other structures asce7 16. I often see roof loads calculated based on the horizontal run of the roof. As a result the live load dead load and distribution of forces are different.

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. For example if building is 24 x 24 and has trusses and the load on the roof will be for 30 lb snow load and a ceiling with no storage will total out like this. If your roof is 1 000 square feet the total snow load is 15 000 pounds of snow. This will amount to twice as much load on the exterior walls compared to a building with a center wall.

But isn t it more accurate to figure the weight of snow and roofing materials by measuring along the actual length of the rafter. 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. This house is identical to our first example except it is stick built. 2attic loads may be included in the floor live load but a 10 psf attic load is typically used only to size ceiling joists adequately for access purposes.

This calculator takes all of this into consideration.