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How to Attach Rafters

Bob Haring

Rafters support a roof, holding its protective covering in place and supporting the various loads or forces exerted by weather. They are angled or sloped from a center peak to walls on two or more sides. All rafters are attached with framing nails, usually 10d or 12d, driven in with a hammer, but specific installations vary according to the type of roof. Some rafters have metal plates at attachment points for extra support.

  1. Attach rafters at two basic points, the peak and the wall. Wall ends are generally attached with a birdsmouth, a triangle cut in the bottom of the rafter to fit exactly over the top plate of the wall, with a vertical end at the bottom. Form peaks either by butting the angled ends (plumb cuts) against each other and nailing from both sides or by installing a center ridge board that goes between the rafters to hold each pair together and all rafters in a series together.

  2. Install rafters with a ridge board by raising the first end pair and nailing the birdsmouths to the wall caps, with the plumb cut ends resting against each other. Set another rafter pair at the other end of the roof, then slide a ridge board between the ends of both pairs of rafters from the bottom. Nail each rafter to the ridge board with the plumb cuts flush against the sides of the ridge.

  3. Nail rafter tops together with the plumb cuts flush against each other. Drive nails from both sides while holding the rafters in place. Add a cross or collar tie to this installation -- a horizontal brace which holds the two rafters together. Place that tie about a third of the way between the peak and the wall top line of the rafter. Miter the ends of the tie to match the slope of the rafters.

  4. Form rafters into a truss. Make trusses by laying rafters in their proper position, putting a bottom chord across the bottom and a cross tie or angled braces between the bottom chord and rafters. Secure all joints with gussets, wood or metal plates which overlap the joints where two boards meet and are nailed to both boards. Attach trusses either through the birdsmouths on the two rafters or through the bottom chord if it rests on the wall.

  5. Add "hurricane" clips to rafters at wall junctions. These are metal plates which overlap the rafter and wall cap boards and are nailed to both pieces. Many jurisdictions now require these to add strength to rafter installations. Similar clips may be used to attach rafter tops to ridge boards.