Attic trusses are sometimes weakened due to heavy loads or dry rotting. These trusses can be strengthened by using some tried and true procedures that have been proven to work in the construction industry. The average do-it-yourself homeowner can complete this project in 1 to 2 days, depending on the size and scope of the project.
Measure the width and length of the truss that needs strengthening. The width will be either 3 1/2 inch or 5 1/2 inch. These are common widths for trusses, which are called "2 by 4's" and "2 by 6's." When measuring the length of the repair area, measure passed the area by 12 inches. For example, if you have a crack in your truss that runs 12 inches along the truss, then your measurement will total 36 inches.
Cut the width and length out of a 4 by 8 sheet of 3/4-inch plywood. Make two marks, one on each end of the plywood, that correspond to the width of the truss. Connect the marks using a chalk line. Make your cuts in the plywood along the length of the plywood, which is also along the length of the wood grain. Cut an additional piece of plywood so that you have one for each side of the truss.
Attach the plywood strips along the length of the truss, one on each side. Apply wood glue to the plywood before placing the patches. Align the plywood so that the centre of the plywood is "on center" with the crack in the truss. Clamp the strips in place using C-clamps. Make sure that the plywood strips align with the edges of the trusses. Insert 3-inch wood screws through the plywood. The screws should penetrate all the way through both pieces of plywood and the truss. Keep the screws off of the cracked or damaged truss area. Instead, place the screws just to the outside of the damaged area within the 12 inches that extend past the crack on each end.