How to Build a Simple Truss

Build the simplest kind of truss with crossties or king posts. Start with a truss plan. Buy a plan or lay one out on graph paper to show the pitch or slope of the roof, the width or span of the truss and the various angles to make a basic triangle of sloped rafters and a horizontal cross member. Use a framing square and circular saw to transfer those angles and dimensions to truss boards, typically 2-by-4-inch lumber. Lengths depend on the width and pitch of the roof; a king post can span only 16 feet, so a truss rafter on a roof that rises 5 inches per foot of run would be about 9 feet.

Make a crosstie truss by cutting two rafters to the pitch or slope and span or width of the roof. Connect those rafters with a crosstie, a horizontal member cut to fit about a third of the way from the peak to the bottom line of the truss. Build a king post by cutting rafters for the sloped roof and a bottom chord to connect the ends of those rafters, with a vertical post in the center between the peak and bottom chord. These boards vary according to the width and pitch of the roof. A roof with a 5-inch rise per foot of run -- half the width of the roof -- might have a 6-foot crosstie with a king post of 3 or 4 feet.

Secure all joints with gussets cut from 1/2-inch plywood and fastened to the connecting boards with 1 1/4-inch galvanized screws and a screw gun. Use rectangular gussets for straight joints where horizontal and angled members meet. Make peak gussets with a horizontal bottom to overlap both rafters and an angled top to conform to the pitch of the rafter peak. Put gussets on both sides of the truss.

Use crosstie and king post rafters only on small buildings, up to 16 feet in width. Expand that maximum span to 22 feet with a queen post style. That is a basic king post with two diagonal braces added, one on each side of the truss, each connecting the bottom of the king post to the center of the sloped rafter.

Expand the truss width to 33 or 36 feet with a Fink (or "W") or a Howe (or "K") style, each named for the inventors and the letter shapes formed by internal triangular bracing. A Fink replaces the king post with two diagonal webs, one on each side of the peak; two run from the peak to about a fourth of the width; and two from that point back to the rafter chord. A Howe retains the center post, adds two more vertical webs halfway between the peak and outer edge, with diagonal braces from the bottom of the center web to the top of the outside webs.