How to Install a Sloping Flat Scissor Truss

Confirm that your sloping scissor trusses will be installed only on outside walls and interior load bearing walls or beams. If necessary, provide additional load bearing support where needed, prior to truss installation.

Erect safe scaffolding at both ends of the truss area making sure that the working height does not require additional ladders or straining while placing the trusses.

Begin laying out the truss placement location from the end wall using the measuring tape and pencil. Most trusses are spaced as directed by the engineering company or architect based on the span. For example, 12 inches on center or 16 inches or 19.2 inches -- this layout number is usually indicated by a red diamond on the measuring tape. Be sure to allow for any overhang. Layout all truss locations on the outside wall as well as the upper wall or beam before continuing.

Place each truss on the floor below the layout location. From the outside tail portion of the truss, make a mark equal to the length of the overhang on the bottom rail. Lift the outside wall end first and slide it beyond the outside wall far enough to allow for safely lifting the other end up to the crew member on the upper wall or beam. It is essential to have at least three members on the crew during this installation. If the trusses are very long, additional members will make the job easier and safer. Ropes may be required.

Place the overhang mark on the truss directly over the outside line of the lower wall also covering the layout mark noted in Step 3 and nail in place using at least four 16 penny cement coated nails and a hammer. The crew member on the upper wall or beam should also nail the truss in a similar manner. Repeat this step for each truss.

Nail a temporary spacing 1 inch-by-4 inch-by-12-foot board onto the top rail of the truss at the mid-span location. This board should be placed after the first four trusses are set. Add additional 1 inch-by-4-inch boards as additional trusses are set. When all are set, this board will be removed as the sheathing is applied.

Install 1 inch-by-4-inch cross bracing between each truss at the lower wall and the upper wall or beam. Additional cross bracing may be used at the mid span for more rigidity. Each truss must also have metal strapping plates or clips installed at each end to provide wind lift resistance. These are designated by the designer and can be purchased at most hardware stores.

Make sure the overhang is straight after all trusses are installed using a string line. Temporarily attach the string to the first and last truss. Each truss should meet this line exactly to ensure the proper distance for the overhang.