Building Your Own Roof Trusses

Pitch and Span Are Key

• The key elements in truss building are the roof pitch, the angle of slope from outer wall to center peak and the truss span or width of the building from wall to wall. The pitch determines the angle that the rafter portion of the truss will be cut. The span determines the basic design and the internal bracing needed. All trusses have two sloping rafters connected by a horizontal beam, or bottom chord, with braces between the rafters and chord at intervals between the peak and wall.

Truss Design

• Study truss design catalogs or manuals to see what style fits your needs. The most basic truss, a king post, has rafters and chord tied with a center post, but it will span only 16 feet. Other styles can span 20 to 60 feet, with varying amounts of space inside the roof for attic storage; some steeper pitch styles can accommodate a room inside the truss. Most house trusses have from four to eight braces set at various angles to brace the rafters against the bottom chord.

Make a Pattern

• Once you have a design, cut a set of pattern rafters, chord and braces. Use a framing square to calculate and mark the rafter angles. Lay the rafters, bottom chord and braces on a flat surface in the proper positions and make pattern gussets of plywood to fit over the joints. Peak gussets should have a flat bottom and top sides that slope the same angle as the rafters. Internal brace gussets can simply overlap where two boards meet or be angled to fit the connection angle, depending on the location and style of joint.

Pattern Gussets

• Mark two sets of pattern gussets for nailing, with the nail holes offset so gussets on each side of the truss do not conflict. Once one pattern truss is built, cut rafters, braces and gussets for all trusses the same way and build them one at a time. Build all trusses on a flat surface, like a driveway, and stack them as they are completed for later installation. Get help; completed trusses will be heavy and require at least two workers to lift.

Metal Gussets

• Some building supply and lumber stores sell metal gussets, which can be used to make trusses. These typically have spikes that are driven into the truss elements to secure the joint and then are fastened with nails or screws. Many experts prefer wood gussets of 1/2- or 5/8-inch plywood; wood gussets generally overlap joints more than metal types and can make a more solid connection.