Building with Trusses

Building a roof? You could dust off your framing square, download and decipher some rafter tables and pop a few nerve pills before struggling to cut and fit rafters, or you could spend a pleasant afternoon by the lake raising a roof the easy way with trusses ordered from the local building centre.

Roof trusses are triangular frames of lumber that form the sloped shape of a roof. Because they are delivered to the building site pre-assembled, they also go up fast (compared to rafters, which are site-cut), and trusses are engineered to allow for wide spans with minimal support. On the downside, the size of trusses makes them challenging to transport to water-access cottages (and they’re often ugly, if you can see them from the underside in the finished building). That said, speed, practicality, and simplicity are why many modern cottage roofs are framed with trusses.

When you order trusses you’ll need to provide the building width and length, the slope and the shape of the roof you want, plus the amount of overhang at the eaves. A computer program does the engineering work, and you can specify rooflines with valleys, dormers, and even loft spaces.

Like many building systems, trusses are strong after they’re installed and all parts are connected, but are floppy on their own—be careful as you move them into position. Small trusses are easy to hoist onto walls, passing them to helpers on scaffolding inside the building for placement and fastening. Metal brackets are much stronger than nails alone for fastening trusses to walls, especially in exposed, high-wind locations. Just be sure to brace your trusses generously as they go up: Wind can easily topple them like dominoes until plywood roof sheathing knits the roof structure together.