How to Install a Roof Truss to Code

Space trusses according to the specific building code in a locale, typically 24 inches on the center of the truss boards; some high wind or heavy snow locales may require 16-inch spacing for some roofs but this is not standard. Mark the caps on both outside walls for truss locations before starting installation.

Measure 1 1/2 inches from the end of the back wall with a tape measure and use a pencil and speed square to draw a line across the wall cap to mark the first truss. Measure 23 1/4 inches and mark the outside line for the second truss. Mark the inside of that truss 1 1/2 inches in. Measure 24 inches and mark the outside line for the third truss. Mark a line 1 1/2 inches in and continue down the roof, marking 1 1/2-inch truss locations every 24 inches. The last space may be slightly less than 24 inches.

Erect trusses starting at the back of the roof; manufacturers will supply two end trusses, which have more vertical bracing than internal trusses. Lift one of those to the roof upside down and have workers on the roof set it upright. Use a level to plumb it; trusses must be perfectly vertical. Brace the first truss with 2-by-4-inch boards nailed to the truss and to stakes in the ground outside.

Fasten the truss ends to the wall caps with three framing nails, toenailed diagonally with a hammer, two on one side of the truss, one on the other. Erect two more trusses, set them plumb and brace them with 1-by-4-inch purlins nailed to the outside of the trusses. Work down the roof, adding trusses, nailing ends to walls with three nails and bracing with purlins.

Install permanent bracing, which will vary with the style of roof and truss. Use purlins connecting the bottom chords of trusses, 2-by-4 diagonal braces tying clusters of three trusses together or whatever bracing system is specified. Check building codes for details for a locale; high-wind areas may require more bracing.

Add truss and hurricane clips. Truss clips are L-shaped metal brackets that fasten to top plates of internal walls and bottom chords of trusses, generally with screws using a screw gun. Place these along every place where a truss meets an internal wall top plate. Install hurricane clips where trusses rest on outside wall caps. Use galvanized nails to fasten these to both boards of the wall caps and to the truss chord, which sits on the wall. Use at least one clip per truss end; high-wind conditions may require two clips per truss.