How to Install Pre-Formed Roof Trusses

Prepare for truss installation by marking the cap plates on the exterior walls. Mark the first truss location, 1 1/2 inches from the end of the wall. Measure 23 1/4 inches from the end wall with a tape measure and mark the outside line for the second truss; trusses normally are spaced 24 inches apart. Mark the inside line for that truss at 1 1/2 inches, then measure and mark 1 1/2-inch wide truss locations every 24 inches. The last location may be slightly under 24 inches. Mark caps on both walls identically.

Erect the first end truss; manufacturers normally supply two special end trusses, which have more vertical bracing. Decide how to lift trusses to the roof. Hire a crane, especially for two-story houses, or use workers on scaffolds on each side of the house or workers with lifting poles on each side of the roof. Lift trusses upright with a crane. Lift the truss upside down manually and set each end on one wall, then have workers on the roof raise it vertically.

Use a level to plumb the first truss vertically and use a hammer to nail its bottom chords to the wall caps with three framing nails, two from one side and one from the other. Brace it with 2-by-4-inch boards nailed temporarily to the truss and to stakes in the ground outside. Raise the second truss, set it plumb and nail it to the wall caps. Add other trusses the same way down the roof. After a third truss is placed, nail 1-by-4-inch purlins as braces, either across bottom chords or across both sides of the top chords. Repeat this pattern down the roof.

Set the other end truss in place once all intermediate trusses are installed. Check all trusses to make sure they are plumb. Install a ridge board at the top of trusses, if that is called for; trusses using a ridge board will have a space at the peak. Install permanent purlins if there is no ridge board and the plans call for these permanent braces, often installed across bottom chords. Some trusses get lateral bracing from the addition of oriented strand board (OSB) decking.

Add hurricane clips at each end of each truss. Nail these metal brackets to the wall caps and to the truss bottom chords with galvanized nails. Many jurisdictions now require these clips on all roofs. Use four nails, two in the truss and two in the wall cap. Set these clips so they will secure the truss but will not interfere with any drywall or ceiling installation.