Roof Load Distribution

Remember these loads are distributed uniformly over the entire surface of the roof.

Roof load distribution.

Live loads and total loads which are dead load live load. You will be designing with two sets of loads. The load bearing capacity of a roof should be adequate to support not only the roof cladding materials such as tiles or shingles but also objects that sit on top of the roof like antennae satellite dishes air conditioning units solar hot water systems and solar photovoltaic panels. Technically you should use the actual rafter length when adding up the weight of roofing materials.

This means that one is a fixed node and the other is a rolling node. Roof uniform load distribution these examples use an assumed load of 40 psf. A clay tiled roof may have a dead load. The load increases with the use of heavier roofing material.

For dead loads you are correct. Here each square foot of roof system delivers 50 pounds of live load and 15 pounds of dead load 65 psf total to the structural support system. However in my practice i typically use the horizontal run of the roof for both types of load. The live load appropriate to your locale is specified by your building official.

The dead load of a typical asphalt shingled wood framed roof is about 15 pounds per square foot.