How to Brace Cathedral Roof Trusses

Brace real cathedral trusses with a center ridge board strong enough to support half the weight of the roof. Have the truss manufacturer calculate this and make a slot at the top of the truss to accommodate it. Build ridge boards typically with 2-by-8 or 2-by-10-inch boards, doubled or tripled as necessary to provide the lateral strength. Fasten these together with framing nails or screws long enough to go through the outside board into another one, using a hammer or screw gun.

Add bracing for the ridge board with vertical posts on end walls, doubled or tripled to match the size of the ridge. Install one post between the peak of the end truss and the top of the end wall plate, another between the wall cap and the floor or foundation. Secure these braces with framing nails or screws long enough to penetrate one board into another.

Place 2-by-4-inch studs on each end wall on each side of the center post. Set these at standard 16-inch stud spacing, but cut them with a circular saw to fit the specific height between the wall cap and the cathedral truss rafter. Fasten these with framing nails, toenailed diagonally into the truss chords and wall caps. Tie the rafters together from end to end by securing them to the ridge board.

Use "collar" ties as an alternative to a thick center ridge board on cathedral trusses. Make horizontal braces to fit between the angled rafters, but place them closer to the peak than ordinary bottom truss chords. Set these about a third of the distance between the peak and the wall. Fasten them with long screws or with bolts in holes drilled with a power drill through the collars and the rafters.

Make special steel "flitch plate" cathedral rafters as another alternative. Have 1/8-inch steel plates welded together at the same angle as the wood truss rafters. Drill matching holes in two rafters and the flitch plate with a power drill and bolt two rafters together around the steel plate.

Connect scissor trusses, which have both top and bottom chords, with purlins, braces nailed between trusses on the inside edges of the truss chords. Nail purlins with framing nails, from the top of one truss to the bottom of the next. Arrange the scissor trusses so a top chord frames the roof for exterior roofing and the bottom chord slopes at a slightly different angle, with vertical braces at the center and on each side and horizontal braces between the vertical supports.