How to Build a Strong Roof Truss

Get the truss span, the width of the roof from wall to wall, which is a key figure in building a truss. Decide on a pitch or slope of the roof, which will determine the height of the peak, and choose a roofing material, both decking and covering like shingles or tiles. Find the length of the house, for the number of trusses, normally spaced 24 inches apart.

Find the roof loads. Figure the dead load, the weight of the truss members, decking and roofing material. Get the live load, mainly snow and ice, from U.S. Weather Bureau tables for your area; this can be significant in cold winter areas and also may influence the pitch, since steep roofs shed snow better. Find the wind load, the maximum force of potential winds affecting the roof, also from the Weather Bureau.

Use these figures to select a truss style. Check local lumber suppliers or look on websites for truss designs and plans. Pick a style appropriate to the look of the house and the projected loads and buy a specific plan, which should include a materials list to tell you what kind of lumber and how much to buy. Have lumber delivered to a work area, preferably indoors, with a firm flat surface.

Use a framing square, tape measure and circular saw to lay out and cut truss chords, two rafters on top and a horizontal chord across the bottom, to the dimensions and angles of the plan. Make internal braces, called "webs," according to the design; all trusses use internal braces between the top and bottom chords based on some type of triangle, but specific lengths and angles will vary with the truss style. Cut one set as a pattern and test fit it and then cut all other components.

Lay out the truss members on a flat surface with the joints properly placed, one set at a time. Make gussets of 1/2-inch plywood, sheets which overlap the seam where boards meet and are fastened to each truss member on the wide edges of the board. Make a peak gusset with a wide horizontal bottom connecting both rafters and a top angled to the peak of the roof. Make rectangular gussets to connect braces with chords and tie the chords together at the rafter ends. Mark gussets using a square and cut them with a circular saw.

Install gussets with 1 1/4-inch ring shank nails and a hammer. Make gussets for both sides of each truss. Predrill pilot holes for nails to insure that the nails go through different points of the truss chord or web and do not conflict. Set each completed truss aside and stack them until ready to set them on the roof.