How to Stick Frame a Gable Roof

Use the pitch and rafter run, or distance each rafter must support between wall and peak, to cut rafters. Lay a 2-by-4-inch rafter board with the 4-inch face up. Put the point of a framing square at the bottom of one end of the board. Align the pitch mark on the thin tongue, such as 5 inches for a 5/12 roof, and the 12-inch mark on the wide blade at the top of the board.

Draw a line with a marker on the angle that forms on the end of the rafter -- this is the plumb or top cut for the peak. Calculate the length of rafter with the "length of common rafter" table on the square's blade. Look under the inch mark for the pitch, the 5-inch mark in this example, to find the differential; it will show 13 inches per foot. Multiply that differential times the rafter run, such as 12 feet for a 24-foot wide roof, to find the bearing point for the rafter.

Measure that length down the rafter from the plumb cut -- in this example that would be 156 inches. Draw a vertical line 1 inch up into the board at that point. Measure 3 1/2 inches back up the board and connect that point with the top of the vertical line to form a triangle, called a birdsmouth, to fit over the wall cap. Add any desired overhang, typically 18 inches, and cut another angle, like the plumb cut but with the point of the square at the top of the board.

Cut all the angles on a pattern rafter with a circular saw. Set it on the roof to make sure the birdsmouth fits firmly on the wall cap and the top cut is at the peak. Cut another 3/4-inch off the plumb cut, at the same angle, to allow for a ridge board. Mark and cut all other rafters the same.

Set the first pair of rafters upright at the back end of the roof, plumb them with a level and nail the birdsmouth of each rafter to the wall caps with three 16d framing nails, two on one side of the rafter, one on the other. Nail 2-by-4-inch boards to the rafters and to stakes in the ground to brace them. Move to the other end of the roof and raise another pair of rafters the same way. Let the rafter tops rest against each other.

Mark a 2-by-6-inch ridge board for rafters. Draw a line 1 1/2-inches from the back end, using a tape measure and a speed square. Measure and mark another line 23 1/4 inches from the end for the outside of the second rafter. Mark the next line 24 inches farther, then measure and mark lines every 24 inches the length of the roof.

Lay oriented strand board panels over the roof joists between the walls to provide a stable work surface. Lift the ridge board to the center of the roof and raise it between the rafters from the bottom. Level it with a level and nail it to the rafters on both sides of each end. Install other rafters in pairs working down the roof from the back. Plumb each set with a level and keep the ridge board level.

Brace the rafters once all are installed. Cut 2-by-4-inch "collar" ties to go between the rafters a third of the way between the peak and the roof bottom. Nail these in place with framing nails. Add a "king" post at each end, a 2-by-4 to fit between the bottom of the collar tie and the end wall cap board. The roof is framed and ready for sheathing and shingling.