Roof Truss Spacing Requirements

Standard Is 24 inches

• Trusses must be spaced precisely to accommodate roof sheathing and roofing materials. Sheathing or decking typically is oriented strand board (OSB), in 4-by-8-foot sheets. The standard spacing for trusses is 24 inches, which works exactly with the 4-by-8 format. The truss pitch or angle of slope does not affect the lateral spacing, from end to end on a roof.

Marking Spaces

• Measure the wall caps on either side, and mark the truss spaces with a pencil or marker. Each truss space will be marked with two lines, 1 1/2 inches apart, with the centers 24 inches apart. Mark the rearmost truss space first. Measure 1 1/2 inches in from the end of the wall and draw a line across the cap board. Mark both outside walls the same, but do one wall at a time.

Second Truss

• Once the first truss location is marked, measure 23 1/4 inches from the wall end and mark the outside line for the second truss. Mark another line 1 1/2 inches from that, then measure 24 inches and mark the outside line for the third truss, with another line 1 1/2 inches down. Follow that pattern the length of the wall. The last space at the end may be slightly less than 24 inches.

Mark Walls the Same

• Mark the other wall the same way. Be sure the marks are identical on both sides. Lift the first truss into place, use a level to set it plumb and nail it to the wall caps. Drive three framing nails at angles with a hammer, two on one side and one on the other. Nail 2-by-4-inch boards to the truss rafters and to stakes in the ground to brace it plumb. Raise and set all other trusses one at a time.

Other Spacing

• Use a similar technique if 16-inch or 12-inch spacing is required by the building code or designers. Mark the first truss with the 1 1/2-inch lines. For 16-inch spacing, measure in 15 1/4 inches for the outside of the second truss, then continue down the roof at 16-inch intervals. Do the same for 12-inch spacing except the outside line for the second truss will be 11 1/4 inches.