Roof Truss Load Transfer

Trusses like all structures are devices for transferring loads from where you don t want them to where you do.

Roof truss load transfer.

The portion of the roof contained between successive trusses is called a bay. Load bearing walla wall specifically designed to transfer a roof load and or upper floor load into the foundation. Loads are transferred downward and outward through sloping rafters the lower ends of which rest on the top plates of the exterior walls. Common design practice for trussed roof and floor diaphragms in light frame construction relies on drag trusses to serve as boundary elements boundary members and their connections and provide the primary and or auxiliary load transfer mechanism configured to carry in plane axial tension and or compression forces to the shear walls below.

They do this by means of top chords which are sloping members that extend from the peak of the roof to the top of the exterior walls at the eaves. Load path loads on the roof are initially supported by the decking. The member spanning from truss to truss which is meant to carry the load of the roofing material and to transfer it on the panel points is called a purlin. Typically roof live load is snow while floor live loads are furniture human occupancy storage.

Roof trusses support a roof s weight by transferring the weight load downward and outward to the building s bearing walls. The roof beams transmit the loads to the ridge beam at one end and a bearing wall or header beam at the other. Trusses must be designed for any special loading such as concentrated loads from hanging partitions or air conditioning units and snow loads caused by driftingnearparapetorslide offfromhigherroofs. A roof truss takes the weight of the roof and the snow on the roof if you live in that kind of climate and transfers it out into the load bearing walls of your house.

To achieve maximum indicated spans trusses may require six or more panels. The purlins transfer the loads to the roof beams as concentrated loads. The decking transfers the load to the purlins. The vertical load on the roof is transferred to the walls.

Hence the length of the purlin is equal to the width of the bay i e the spacing of the trusses.