A broken roof truss can cause many different problems. If the truss is bad enough, it can cause the sagging or collapse of a roof. The good news is that the problem can be fixed fairly easily with a few materials, a helper and diligent application of the steps below.
Assess the situation. When working in tight and cramped quarters in the attic, be careful where you step. The rafters are spaced at 24 inches apart and the area in between will easily fall through into the room below. If you put any pressure on the ceiling material, which is applied to the underside of the rafters, it will collapse. Place a few scrap 2-by-8 boards across the top of the ceiling rafters. This will give you a temporary floor to stand on.
Determine the size of the roof truss to be repaired. Trusses come in different lumber widths (2-by-6 or 2-by-8). You can do this by measuring across the width of the truss. A 2-by-6 truss will measure 5.5 inches and a 2-by-8 truss will measure 7.5 inches.
Cut two pieces of lumber 4 feet long for the first phase of the repair. These will serve as patches to be installed on each side of the broken roof truss.
Attach the truss patches. Place the 4-foot board against the flat side of the broken truss, making sure that the same amount of patch rests on either side of the break or that the break is centered in the middle of the patch. Secure the patch on one side of the break with the wood screws and have your helper apply up pressure until the truss in realigned. Secure the other side of the patch with wood screws.
Apply the second patch to the other flat side of the truss and in line with the first patch. Secure evenly across the board with wood screws. The roof truss will regain its strength with the repairs.