Basic Roof Truss Theory

Design

• A well-designed roof truss replaces rafters and offers a stronger design. Smaller pieces of wood, when assembled in a strong design, can offer just as much support for a roof as a single large beam. The result is a truss that can accomplish the same thing while using much less material, making it less expensive and easier to transport and install. Trusses can be manufactured in a wide range of designs and sizes, making them appropriate for many different kinds of roofs.

Stability

• Once trusses are assembled and in place, they provide a very stable support for a roof. The trusses are strengthened not only by their own design but by the bracing that connects them to each other and by the roofing material itself, which prevents the trusses from racking to the left or right. Because the trusses are manufactured to be identical, the roofing surface is completely flat, making the entire assembly rigid and resistant to wind and weather.

Triangles

• Aside from a circle, the triangle is the most stable shape because it only has three sides. Unlike a square, triangular frames won't change shape when subjected to stress, unless one of its points actually separates. Trusses are manufactured as a series of triangles to take advantage of this fact. The overall shape of most trusses is a triangle, or a series of triangles, to create a pointed roof that will shed snow and rain. The large triangle is reinforced with diagonally placed interior struts, creating a series of sturdy triangles that are resistant to sagging and warping.

Cost

• In addition to using less material, trusses also require less labor than installed rafters because they are manufactured in a factory. Building something in a factory is easier because permanent tools are in place and workers don't have to work in the uncertain conditions that exist on a roof. The result is less time spent building a truss, allowing manufacturers to sell them at a lower price.