Rafters serve a critical function in a home. Rafters support the roof deck which is comprised of the roof sheathing, underlayment and roof covering. A rafter could become damaged from an excessive load, such as snow or ice, or water entry if a leak goes undetected. When done correctly, applying a scab to a damaged rafter will not only return the rafter to its original load-bearing strength but it is also much cheaper and easier to do than replacing the entire rafter.
Measure the width of the damaged rafter. Purchase a minimum 6-foot long scab beam of the same width as the rafter. The scab repair should extend at least 3 feet away on each side from the damaged area on the rafter.
Cut the scab into a 6-foot length. Press it up firmly against the rafter, so the widths match. For example, if you have a 2-by-6-inch rafter, place the 6-inch width of the scab against the 6-inch width of the rafter. Be sure to leave 3 feet on each side of the scab so you have good solid wood to screw the scab into.
Hold the scab firmly in place and drill pilot holes for the screws in a zigzag pattern. Start the pilot holes 6 inches from the edge of the rafter damage and work back to the end of the scab beam.
Insert a screw into each pilot hole and drive the screws firmly into the existing rafter. Do this for both ends of the scab report. Repeat this same procedure to apply the scab to the other side of the damaged rafter.
Use screws, not nails to attach the scab because screws provide greater strength and support.
If more than one rafter is damaged consult a structural engineer to determine if the rafters need to be replaced.