Correct Spacing for Roof Trusses

Space Variations

• Trusses are used in about 80 percent of new houses and virtually all are made of pine or fir lumber. Most trusses are made with 2-by-4-inch boards. Some roofs with heavier load factors or special conditions may use 2-by-6-inch or even 2-by-8-inch lumber. Heavier lumber can affect spacing. A 2-by-4-inch truss may require closer spacing than a 2-by-6 in the same weather areas.

Standard Spacing

• Most trusses are spaced 24 inches on center, which means the centers of the truss members are 2 feet apart laterally. Building codes in some severe weather areas or governing roofs in special situations may require 16- or even 12-inch spacing, but 24 inches is the universal basic dimension.

How to Space

• Spacing trusses correctly requires marking the cap plates on the outside walls. Two techniques are employed: using either a framing square or a tape measure. A framing square has two arms, a tongue 1 1/2 inches wide -- which is the width of a standard truss board -- and a blade 24 inches long, which is the standard spacing. Mark the truss width with the tongue, and use the blade to mark the spacing. Using a tape measure requires stretching the tape across the top of the wall cap.

Marking Spaces

• Mark the first truss from the back end of the roof, then measure 23 1/4 inches to mark the outside line of the second truss. Mark the inside of that truss at 1 1/2 inches, then measure from that line 24 inches down the roof, marking the 1 1/2-inch width at every location. The last truss dimension on most roofs will be slightly under 24 inches.

Other Spacing

• Use the same technique if 16-inch spacing is required. Mark the first truss, measure 15 1/4 inches in from the end wall to mark the outside line of the second truss, then proceed down the roof. The same procedure would apply to 12-inch or any other spacing.