A well-constructed roof system is essential to a structurally sound building. Roof rafters run from the ridge board that runs along the centre of the building to the top plates of the exterior walls. They support the roof decking and shingles and transfer the load down toward the foundation. Rafters vary in length based on the width of the house and the slope of the roof. Given the roof's importance to structural integrity, roof framing is best left to professional carpenters or experienced do-it-yourselfers.
Mark the required angle, using the carpenter's square, on the rafter end to be attached to the ridge board. The roof's slope determines the cut angle and can be found on the building plans.
Hold the end of the rafter against the ridge board. The acute end of the rafter should be even with the top edge of the ridge, and the bottom should be two inches above the bottom edge of the ridge.
Nail the rafter to the ridge with nails angled through the side of the rafter and into the ridge. Nail the opposite end of the rafter to the top plate of the exterior wall.