How to Join Roof Rafters
Rafters are used in all types of roof framing. Even roof trusses, the most popular method of framing today, use rafters, although they are called top chords in trusses. They support the load on a roof, from the weight of the roofing to snow and ice accumulations and the force exerted by wind striking the roof.
They are the traditional form of roofing, dating back to when man first laid a couple of logs across some walls and covered them with brush.
Join rafters at the top or peak, either to each other or to a centre ridge board. Join rafters on the ends to wall caps, the top boards on the outside walls, which actually bear the weight of the roof. The traditional method of joining is framing nails, 10d or 12d, which are long steel spikes hammered through one piece of wood into another.
Install rafters at the wall by nailing framing nails with a hammer through the birdsmouth or bearing point notch, cut in the bottom of the rafter to fit securely over the cap board. Drive two nails, one in each side of the birdsmouth. Secure this joint with hurricane straps, which are metal connectors that overlap the rafter and wall cap and are nailed to both pieces. Some building codes now require these on all roofs as an extra precaution against wind loads.
Connect rafters at the peak with a ridge board or with gussets. A ridge board runs between pairs of rafters the length of the roof, to form the actual peak. The angled tops of rafters are nailed to the ridge board, two nails in each rafter. Gussets are an option on some roofs if they do not rely on a ridge board but use the rafters to form the peak. Gussets may be wood or metal. They are triangles shaped to connect the angled cuts of the rafters, from the very peak down to below the bottom of the rafter joint. They are nailed across the rafters to join them securely.
Add extra strength to rafter joints, with or without ridge boards, with cross or collar ties. These are rafter boards cut with ends angled to fit the angle of the outside of the rafters and fastened between two rafters below the peak. You can add collar ties on the outside faces of the rafters or cut to fit inside the rafter triangle; the latter are fastened with wood or metal gussets on both sides of the ties.