How to Replace a Roof with Attic Trusses

Remove the old roof in stages. Peel off shingles with a shingle scraper, which is a long-handled tool with a wide blade that you can slide under the shingles to pull them up. Take off roofing paper or similar underlayment. Strip the wood roof decking; lift wood sheets at nail points with a pry bar, and pull the nails with a claw hammer. Take down the existing rafters or trusses by removing the fasteners on the wall plates. Put all the old material in a construction dumpster.

Inspect the top of the wall caps. Remove all remaining nails or fasteners, such as hurricane clips. Repair damaged sections, or replace cap boards that are split or seriously damaged by pulling off the old boards and nailing on new caps with 16d framing nails and a hammer.

Measure the roof's width and the length to determine the size and number of prefabricated attic trusses needed. Check with the supplier of the trusses for type; all attic trusses have bottom chords from wall to wall that form an attic floor, vertical bracing that forms a room, diagonal bracing for support and a wall top plate under the angled rafter chords. Decide how much space you need and how trusses should sit on the wall, with the bottom chord or the rafter as the bearing point.

Mark truss locations on the wall caps. Measure 1 1/2 inches inward from the end of the back wall, and use a speed square and pencil to draw a line across the wall cap. Measure 15 1/4 inches inward, and draw another line to mark the outside edge of the second truss. Based on that line, measure 24-inch increments across the roof's length.

Attach two lifting straps at about the midpoint on each prefabricated attic truss rafter and a guide rope to the bottom chord that a worker can use to help direct the rafter into position. Prepare bracing boards with stakes in the ground outside the wall. Have a crane's operator use the vehicle to raise the first truss onto the roof. Use the guide rope to move the truss until workers on the roof can place it in the proper spot, at the first 24-inch mark you made earlier, and fasten the truss to the wall caps and braces.

Set the truss plumb, or straight, by using a level. Fasten the truss to the wall caps with 16d framing nails, driving them diagonally through the truss chords into the wall caps. Use three nails per rafter, two on one side of the chord and one on the other side of the chord. Nail the bracing boards to a truss web or brace and to stakes in the ground to hold it plumb.

Install other trusses one at a time until all are secured to the roof at the 24-inch increment marks. Add temporary purlins or horizontal braces of 1-by-4-inch boards on top of the rafters to secure the trusses laterally. Put permanent bracing in as recommended by the truss manufacturer; the permanent bracing may be boards nailed across the internal truss webs or braces or boards nailed diagonally from the top of one truss to the bottom of another truss. Bracing varies by roof and truss.

Secure every rafter chord to a wall plate by using metal hurricane clips attached with 8d galvanized nails Put two nails into the part of the clip that goes over the wall cap and two nails into the part that ties into the rafter. Finish the roof with oriented strand board decking, roofing paper and shingles as desired; those items vary with the type of roofing you use.