A roof truss is a building material used to frame and support the roof structure of a home. While traditional roof framing was built on-site using lumber or steel, the majority of new homes today are built with pre-manufactured truss systems. There are many different types of roof trusses available to accommodate different home designs and roof loads.
While many different trusses are available for roof construction, they can usually be broken down into one of two basic categories. Flat trusses, known as parallel-chord or girders, are used to construct flat roofs. Pitched, or common, trusses are used to build sloped-roof structures. Hip, gambrel or bowstring designs are popular examples of common trusses.
All types of trusses have the same basic components and structure. The name "truss" describes a triangular design, which may range from a simple individual triangle to a large number of interconnected units. The outside framing members are known as chords, while the smaller connecting members are called webs. A point where the truss rests on a load-bearing wall is known as a bearing point, and a king post is a vertical support that divides the bottom chord on many types of trusses.
Roof trusses are used to carry and support the weight of the roof deck and any finish material used to cover the roof. This weight can be quite significant if clay or slate roof tiles are used, or it may be very light when used to support asphalt shingles or rolled roofing. The chords support the roof while the webs brace and stabilise the chords, helping to distribute the load across the entire truss to the bearing walls on either side.
One of the primary benefits to truss construction is the ability to span much longer areas than with traditional stick framing. Because trusses are designed by engineers, they are also safer and more reliable than alternative materials. Truss roof systems can be erected much more quickly and efficiently than framed roofs, and a variety of different truss designs are available offer versatility to builders and homeowners.
Because of the triangular shape of a truss, homeowners will find that roof trusses can greatly reduce the amount of usable space in the attic. This can cause problems with storage, or may even cut into potential living space. Trusses are also generally more expensive than stick framing in terms of upfront cost, though the associated labour savings may offset this higher material cost.