Rolling Roof Trusses
Factory-made trusses save time and give you a roof engineered for strength and stability.
Synopsis: A veteran frame carpenter walks you through the process of installing simple gable trusses by hand (no crane involved). He offers tips for getting the job done quickly and accurately, along with guidelines for bracing the trusses.
Roof trusses offer many advantages. They are lightweight (generally made from kiln-dried 2x4s), so they are fairly easy to handle. Because trusses are engineered, they can span longer distances without having to rest on interior bearing walls, allowing for more flexibility in room size and layout. Finally, installing trusses on most houses is pretty simple. If you want to get a house weatherized quickly, roof trusses are the way to go. Ceiling joists and rafters are installed in one shot, and no tricky cuts or calculations are required.
Lay out braces as well as plates
Laying out the top plates for trusses is the same as for roof rafters. Whenever possible, I mark truss locations on the top plates before the framed walls are raised, which keeps me from having to do the layout from a ladder or scaffolding. For most roofs, the trusses are spaced 2 ft. on center (o.c.). I simply hook a measuring tape on one end of the plate and mark the truss positions every 2 ft., putting an “X” on the far side of each mark. I also mark the layout on several 16-ft. 1x4s, which serve as top-chord braces during installation.
A straight fascia is just a snap away
Remember to order trusses well in advance of when you’ll need them. In Oregon, where I work, a three-week lead time is common. Before I ask for truss delivery, I make sure all the exterior and interior walls are upright, nailed off, and braced properly. Interior walls help to keep the exterior walls straight and plumb. In addition, with all walls in position, I have more support for the bundles of trusses when they’re delivered.
Even when the walls are straight, it’s worth taking some trouble to ensure that when the trusses are installed, the rafter ends line up perfectly. There’s an easy way to do this.
I measure in 1 in. from the outside edge at each end of the top plate. Then I snap a chalkline the full length of the wall as a straight reference line. As I set each truss, I measure from the tail of the rafter chord the distance of the eave overhang plus 1 in. I mark this point on the bottom chord of each truss and align the mark to the snapped reference line, keeping the ends of the trusses straight.
I also snap a chalkline along the gable endwall plates to locate and align the gable truss. Unless it’s required by code, I usually don’t sheathe gable trusses. The gable truss is set flush with the outside face of the wall sheathing below. I snap the chalkline along the gable end-wall plates 1 in. from the outside. When the gable truss is set on this line, it overhangs the right amount.
Cutting blocks to nail between trusses is another important step to complete before you start setting trusses. In seismic and highwind areas, code requires blocking between trusses at the plates and often at the ridge as well. I cut 22-1/2-in. blocks to maintain the 24-in.-o.c. truss spacing and to help keep the trusses stable as they go up.
From Fine Homebuilding #168
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