How to Construct Timber Roof Trusses

Veronica R

Hupome Ranch - Exterior at Night   View this Photo

The roof is probably one of the most, if not the most important part of a building as it protects everything inside a building - including its occupants. The roof truss is a strong, triangulated framework usually made from timber and provides support for a roof. Trusses, which may be custom built, are usually named according to their shape such as king or queen trusses, clerestory, fan or gable trusses.

Choosing the Lumber
Knowing how much weight the truss will support will determine the thickness of the timber used. Generally, 2x6 or 2x8 size timber is chosen for larger structures and 2x4s for smaller structures, such as sheds. The timber that will support the most weight and cause the most stress on the wood, such as the top chords and the bottom pieces of the truss should be of the highest quality. To avoid shrinking and warping, the timber should be kiln dried and straight grained and dense boards with no obvious splitting should be used.

However, if the timber is slightly curved, the curve should be facing downward so that the curve is flattened out when weight is put on the truss. Choose high density softwoods like southern yellow pine, spruce or fir, and also make sure they are not twisted or crooked.

The first step to construct a roof truss is to determine its design and to ensure that it is being built to code. Once you have the design in place, all the materials such as the timber, hammer, connector plates, a saw, a saw horse, clamps, screws and nails should be purchased. The timber should be cut based on the size of the roof and specifications in the design. Once you have all the pieces, you can start to build the trusses - preferably on a surface that is as smooth and flat as possible. The steps include marking the top cuts on the top chords where they meet at the roof peak, determining if the top or bottom chord will have an overhang and locating the position of the diagonal bracing members.

Other points to consider when constructing the truss are whether you will connect all points of the frame members using reinforcing plates or gussets. Once the trusses have been assembled and before they are installed, they should be stacked flat to prevent them from warping and to ensure that they match in terms of size. The trusses should be securely installed on the structure.

One of the considerations for building timber roof trusses is to use high quality materials and experienced workers. When building timber roof trusses, labor, materials, equipment, and scrap disposal costs should also be considered.

What do you think is the most challenging part of constructing timber roof trusses?

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Answers (2)

Veronica R • Jan 5

Yes, I will need to find a better photo showing truss framework next time and not just the triangular roof characteristic of truss construction.

Les M, Architect • Dec 27

Can't see a truss in the photo - please explain. Looks more like portal construction.