A truss is composed of triangles because of the structural stability of that shape and design. A triangle is the simplest geometric figure that will not change shape when the lengths of the sides are fixed. In comparison, both the angles and the lengths of a four-sided figure must be fixed for it to retain its shape.

Roof

This house uses trusses for the roof framing. Trusses are pre-fabricated, triangulated wooden structures used to support the roof. The alternative is to build up the roof’s frame with 2×8s and 2×10s. Trusses are quite common these days because they have five big advantages from the builder’s standpoint:

• Trusses are incredibly strong.
• Because they are built strictly from shorter lengths of 2×4 lumber, they are generally a lot less expensive than the alternative.
• You can have just about any shape custom-built, and this allows interesting features like cathedral ceilings at low cost.
• You can span a large distance with a truss and the truss transmits all of the weight to the exterior walls. Therefore, none of the interior walls are “load-bearing,” so they can go anywhere and are easily moved later.
• Trusses go up quickly!

From the homeowner’s standpoint, the one big disadvantage is that you don’t have any attic space.

Trusses come in several standard configurations:“W” truss,“M” truss, “Scissors” truss, “Gable” truss.