Trusses Make a Stronger, Straighter Roof and They Go Up Quickly
Bird's eye view
Assembled at the factory, trusses reduce labor and material costs
Trusses can be ordered for just about any roof configuration and are made from smaller lumber sizes than dimensional rafter stock. They are assembled by the manufacturer in jigs using pieces engineered specifically for the application, which translates into consistency and precision, and they can be boomed into place quickly once they’re on the job site.
Trusses can be made from stock that might not work in other applications
Trusses are manufactured in a variety of standard configurations and can be fashioned into just about any type of roof. Builders can special order trusses to fit the job.
Strongly consider raised-heel trusses to permit more insulation
Roof trusses made from 2x4s can span distances up to 34 ft. on a roof with a pitch of 5 in 12 or greater. When made from 2x6s, trusses can span up to 56 ft. without any intermediate supports.
Like engineered rafters, roof trusses permit longer clear spans than conventional sawn rafters, giving the designer more latitude in homes with large rooms. But last-minute design changes are much more difficult to implement than they would be for a conventionally framed roof.
In all but the mildest climates, it makes sense to order raised-heel trusses, which provides extra depth at the eaves for insulation.
Handle with care until they're in place
Although trusses are very strong, they are unwieldy. They don’t have much strength until they are set in place vertically and they can be stressed or damaged if they’re handled carelessly on site. Large trusses should be placed with a crane. Smaller trusses can be tipped into place with one or more long poles. In all cases, they must be braced to prevent tipping or even collapsing until roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. is applied.
Trusses are engineered. Manufacturers design trusses for specific applications. They can’t be modified in the field if something doesn’t fit. If a truss is damaged on site, the manufacturer should be contacted for help in devising a fix.
Section 802.10 of the International Residential Code covers engineered roof trusses. The code prohibits drilling, notching, or modifying trusses. It's important to adequately plan for mechanical equipment so as not to exceed the design load [802.10.4]
Illustration: from Code Check Building 2nd Edition. click to buy .
ABOUT ROOF TRUSSES
Roof trusses are increasingly common in residential construction, accounting for roughly two-thirds of the U.S. market for new houses built in the U.S.
Trusses reduce labor as well as materials costs, as a 1996 study by the Wood Truss Council of America and the Building Systems Council of NAHBNational Association of Home Builders, which awards a Model Green Home Certification. discovered. “Framing the American Dream” presented a comparison of labor and materials costs in two identical 2,600-sq. ft. houses, one built with engineered components and the other framed conventionally. Using roof trusses saved a total of 156 hours of labor and 4,190 board feet of lumber.
Another advantage: Some manufacturers are making roof trusses from lumber that is certified by the Forest Stewardship Council(FSC) Nonprofit organization that promotes forestry practices that are sustainable from environmental and social standpoints; FSC certification on a wood product is an indicator that the wood came from a well-managed forest.. The Hayward Corporation of Monterey, Calif., is one firm that makes trusses from 100% certified wood. TrusPro Inc., of Guadalupe, Calif., is another.
Drywall, Wood, and Truss Uplift
- Donald Blum/Fine Homebuilding #168
- Courtesy Wood Structures, Inc./Fine Homebuilding #89
- Christopher Clapp/Fine Homebuilding #89
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