Building Construction Basic Roof Framing

Rafters

• You still can frame a roof with joists and rafters. The most complex part of this is cutting rafters correctly, so they meet at precise peaks and sit securely on top of walls. This can be done using a framing square and a circular saw, but requires carpentry expertise. Rafters generally are connected at the peak by a ridge board, a long board the length of the roof between the angled ends of rafters. They also are braced laterally sometimes with purlins, boards nailed horizontally between rafters.

Trusses

• Framing a roof with trusses can be done by less-skilled carpenters. The key to truss framing is marking the trusses. That is done with a tape measure, speed square and marker. A framer gets on a ladder to reach the cap boards on each wall. Truss boards are 1 1/2 inches thick, so locations are marked on both sides of the roof with parallel lines 1 1/2 inches apart and centers spaced 24 inches apart. Trusses may or may not require a ridge board.

Spacing

• Spacing is critical with either trusses or rafters, but is easier with trusses. The first location is marked 1 1/2 inches from the end of the back wall. The second is marked with the outside edge 23 1/4 inches in from the wall end, with a second line 1 1/2 inches farther. Other locations are marked with outside lines 24 inches apart, so centers will be exactly 2 feet apart. The last space is usually slightly under 24 inches, to conform to 4-by-8-foot panels of roof decking.

Fastening

• Trusses or rafters are fastened to wall caps with 16d framing nails, three per board, driven diagonally into the cap boards. Two nails are put on one side, one on the other. Trusses or rafters also need to be secured with "hurricane" clips, metal brackets nailed with galvanized nails to both the wall cap and the truss or rafter board. Trusses also require some lateral bracing, usually purlins placed diagonally between truss chords at the top and bottom of each truss.

Plumb

• Either trusses or rafters must be set plumb, exactly vertical. Rafters are nailed in place by carpenters on the roof; typically, end rafters are set in place first and tied together with a ridge board with rafters nailed to it from the side. Trusses are lifted to the roof as a unit, upside down, set upright and secured with nails to the wall caps. The first rafters or truss are braced plumb with boards nailed to them and to stakes in the ground outside.