How to Lay Out Roof Trusses

Start at the back end of the roof to mark the wall caps on both sides of the house, one at a time. Get on a ladder and measure 1 1/2 inches into the house from the end of the back wall with a tape measure and use a framing square or speed square to draw a line with a pencil or marker across the wall cap. Move the ladder as you work so you are always looking right at the truss location.

Measure 23 1/4 inches in from the wall end and draw another line for the outside of the second truss. Measure 1 1/2 inches and draw a second line for the inside of that truss. Use a tape measure and speed square to mark the parallel lines or use the thin tongue of a framing square, which is 1 1/2 inches wide, as a guide. Place the square along the side of the wall cap with the tongue across the board and mark on both sides to show the truss space.

Move 24 inches from that second inside truss line and mark another set of lines 1 1/2 inches apart. Continue down the roof, marking 24 inches from the inside line of one truss to the outside line of the next. The last space may be slightly less than 24 inches. Use a tape measure to get the 24-inch and 1 1/2-inch spaces and draw lines using a speed square or use the 24-inch long blade of the framing square to mark the spacing.

Go to the back of the second wall and mark truss spaces along it the same way. Test your marks in a couple of places by pulling a string line across two wall marks and checking it with a square to make sure the lines are square and even, so trusses will be set with centers exactly 24 inches apart.