Roof Framing 101
These days’ wider rafters are often used than are suitable for the fascia, so the tail of the rafter is also cut to create a narrower, more suitable fascia board. This requires laying out a level line on the tail of the rafter. To do this, do not make the tail cut until this has been established. Draw the sub fascia and finish fascia board on the end of the rafter and against the plumb tail cut. Use the bottom edges of these boards to mark the level line cut. Again, once all cuts have been marked, cut the pattern rafters, test and you’re ready to erect the roof framing.
Before beginning the framing, determine rafter location on both top plates and mark them using a framing square. The small or tongue side of the square is 1-1/2 inches wide so you can mark the locations of both sides of the rafters to guide the installation.
The easiest method of erecting the rafters is to make temporary braces of 2-by materials. These should be the height of the building walls, plus the rise. Use only enough supports for the first length of ridge board. Rip the ridge board to the correct width to meet the rafter widths at the ridge. Create a saddle at the top with the braces the height of the building walls, plus rise, less the width of the ridge board. Brace these supports in the centerline of the building. Position a ridge board down in the saddles of the supports. Align the top plumb cut with the ridge board, and align the heal cut of the bird’s mouth with the inside of the wall. Nail the rafter in place. As the rafters are installed, add any supports needed or required by code, such as collar ties or center supports. Continue erecting rafters until you reach the end of the firs piece of ridge board. Then move the temporary braces for the next ridge board and continue installing rafters.
With the rafters in place, the gable end framing uses vertical studs, or “blocking,” positioned directly over the wall studs and supported by the end top plates. They are notched to fit around the gable-end rafters. After the sheathing is installed, hanging or “fly” rafters are then installed.
Roof framing doesn’t have to be daunting, but if it’s your first try, a simple gable roof, say on a garden shed, is the best bet.