When installing a roof truss, it’s absolutely critical to exercise extreme caution and follow all of the manufacturer’s directions. Improper installation can cause roof truss failure and structural collapse, leading to injury or death. Roof trusses must be handled gently and from the top down. They are designed to withstand vertical pressure but not horizontal pressure. Small trusses can be installed by a crew of two to three workers. However, installation of trusses longer than 60 feet requires a professionally engineered bracing system.
Step 1 – Measure and Obtain Trusses
Measure the area to be framed and plan for the number of trusses you will need. Also plan for the temporary restraints required to brace the trusses during framing. The spacing of the trusses and their restraints depends on the span of the trusses. Check the manufacturer’s specifications and guidelines published by the Structural Building Components Association. If you purchase prefabricated trusses, they may come already separated by 1x4 boards. Mark anchor points every 2 feet to guide installation.
Step 2 – Lift Trusses Onto Roof
The help of a second or third person is necessary even to lift a truss onto a single story roof. It is best to brace the inside of the trusses before handling them. Use a t-brace to support the truss vertically. Install 2x4s at a 45-degree angle. Nail braces vertically every 4 feet along the top and bottom of a gable truss. Turn the truss upside down and place on corner on the roof surface. Slide the rest of the truss up, using a 2x4 as a ramp if necessary. Lifting trusses higher than one story may require a crane.
Step 3 – Brace First Truss to Ground
The first truss of the installation should be braced to the ground on the interior or the exterior of the building. Brace the truss on the interior if the ground outside of the building is not level. Begin installation at a solid starting point such as a braced gable end or girder offsets.
Step 4 – Install Temporary Bracing
Hold the trusses in place once temporary lateral and diagonal bracing. Check the manufacturer’s specifications to find the location of the top chord temporary lateral restraint. Locate additional restraints at pitch breaks, and install vertical braces at their locations. Set each truss after the first with its top chord temporary lateral restraint aligned with the ground bracing. Use wooden 2x4 or prefabricated metal braces as short member temporary lateral restraints between the trusses. Hold these restraints in place with two nails each. Install top chord diagonal bracing and web member diagonal bracing to form triangles perpendicular to the plane of the truss. Install the bottom chord lateral restraints and diagonal bracing.
Step 5 – Connect Trusses Permanently
Connect the end jacks to the wall and girder early during installation to maximize stability. Use hangers and tie downs to join the trusses permanently to the bearings. Install plywood roof sheathing over the trusses by joining panels every 2 feet with nails or H-clips.