Rafter ties are always required unless the roof has a structural (self-supporting) ridge, or is built using engineered trusses.Rafter ties should be at least 2 x 4 inches (nominal). When ceiling joists run perpendicular to the rafters, inspectors may find rafter ties installed above ceiling joists as framing members every 4 feet running above the ceiling joists connecting opposing rafters. A rafter tie forms the bottom chord of a simple triangular roof truss. A sagging ridge is one indication that the roof structure may lack adequate rafter ties. When the walls spread, the ridge board might sag. They help keep walls from spreading due to the weight of the roof. Rafter ties resist the outward thrust that rafters exert on the exterior walls. ![]() Rafter ties are installed between opposing rafters, and they should be installed as close as possible to the top plate. The roof framing mock-up below shows a standard rafter tie. In many situations, you'll find that ceiling joists installed parallel to the rafters are intended to function as rafter ties.
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