Rafters are the beams that run just under the roof of a home and represent the roof's angle. Joists are the horizontal beams that run just above the ceiling and anchor the rafter. Where these two housing frame components meet, they must be attached securely in order to ensure the stability and longevity of the roof.
Check the angle of the joists to ensure they are horizontal before attaching them to the rafter. Lay a water level on the top of the joist or check the angle with a laser level. If the joist does not sit perfectly level, then the wall heights must be corrected before the joists are attached.
Ensure that the ends of the joists that may project above the rafter are trimmed off before attaching the joists to the rafters. Use a table saw to cut off the angle that projects over the rafter.
Set the end of the joist on top of the wall (the other end of the joist should rest on the opposite wall). The trimmed edge of the joist should be up. Set the notched end of the rafter on the wall so that it sits flush with the top edge of the wall. Have a partner hold the rest of the rafter in place while you connect the joist and the rafter. The rafter and joist should sit flush against one another.
Attach a seismic anchor to the side of the rafter opposite the joist. Seismic anchors are joints with a 90-degree-angle twist that connect the rafters directly to the wall.
Nail the joist to the rafter. Use at least four nails per joist/rafter connection. Nails should be at least one and a half times the depth of the rafter and joist beams. Usually, these beams are 2-inches by 4-inches, and so the depth is 2 inches. Thus, the nails should be three inch long wood nails.
Test the rafter/joist attachment manually for stability by rocking it with your palm. For added stability, pre-drill holes for screws and anchor with 3-inch wood screws.