Trusses are engineered wood products used for structural support in roof structures of single- and multi-family residential and non-residential construction. Each truss is a frame composed of shorter lengths of lumber, which can be custom-designed for a particular end use. Light-frame trusses have replaced traditional larger solid-wood rafters in roofing structures, reducing the amount of wood needed and getting more from each tree harvested.
Machine stress rated lumber of varying strengths is normally used in the production of trusses, depending on end-use requirements. Within a single truss, several grades of MSR lumber will also be used, depending on the requirement of each piece as calculated according to engineering principles.
The chords and webs are connected by steel connector plates (“truss plates”). In pitched chord trusses, the top chords meet to form the apex of a triangle. In parallel chord trusses, used for flat roofs, the top and bottom chord are arranged in parallel. Complex and intricate shapes specified by building designers can also be produced. The attic space normally found with more traditional roofing designs is often lost with trusses.
Light-frame trusses are relatively cheap, easy to fabricate and simple to erect on site.
Pitched chord trusses are used extensively as support for roofs in residential construction in North America, where they are used in over 90% of all new single-family residential construction. Most of these light-frame trusses are produced in relatively small local assembly facilities to facilitate transportation of these awkward shaped items, although some are constructed on site.
Sales of trusses follow the new residential construction and repair and remodelling market, with the size of the U.S. market dominating demand. Parallel chord trusses are used predominantly for multi-family or non-residential buildings. They are a low-cost alternative to steel, but growth is restricted by their susceptibility to fire.
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