Roof Load Distribution

A clay tiled roof may have a dead load.

Roof load distribution.

The load increases with the use of heavier roofing material. Live loads and total loads which are dead load live load. 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. Remember these loads are distributed uniformly over the entire surface of the roof. In order for a roof truss load to be stable you need to assign two of your nodes on each truss to be support nodes. A fixed node will provide support in both directions down the length of the roof truss members often called the x and y directions.

This means that one is a fixed node and the other is a rolling node. The dead load of a typical asphalt shingled wood framed roof is about 15 pounds per square foot. To do this i use conservative too heavy dead loads and full snow loads regardless of pitch. Technically you should use the actual rafter length when adding up the weight of roofing materials.

Roof uniform load distribution these examples use an assumed load of 40 psf.