Roof Load Distribution

The live load appropriate to your locale is specified by your building official.

Roof load distribution.

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. For dead loads you are correct. The dead load of a typical asphalt shingled wood framed roof is about 15 pounds per square foot. Remember these loads are distributed uniformly over the entire surface of the roof.

To do this i use conservative too heavy dead loads and full snow loads regardless of pitch. 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. Roof uniform load distribution these examples use an assumed load of 40 psf. A fixed node will provide support in both directions down the length of the roof truss members often called the x and y directions.

Technically you should use the actual rafter length when adding up the weight of roofing materials. The load increases with the use of heavier roofing material. A clay tiled roof may have a dead load. However in my practice i typically use the horizontal run of the roof for both types of load.

This means that one is a fixed node and the other is a rolling node.