What building supply retailers can expect from truss fabricators

G INCEover50% of thesinglefam9 ilv houses built in the U.S. use wood roof trusses in their construction, these engineered wood products can generate significant profits forthe lumber and building material supplier.

The industry has grown to about 2,000 manufacturers since metal plate connected wood trusses were introduced some 40 years ago. Many lumberyards operate their own truss plants and others deal with truss manufacturers on behalf of their builder customers.

Because trusses are the result of special engineering and fabrication, the building supply retailer is dependent upon the fabricator to produce the product his builder customer needs. The dealer should be sure that his fabricator provides the necessary engineering support. The truss supplier shouldbe responsible for specific technical items:

Sealed engineering drawings: Every truss design, from the simplest single pitchhouse truss to a complex hip truss with vaulted ceilings or long-span post framebuilding truss, should be accompanied by a drawing sealed by an engineer licensed in the state where the truss is to be used.

The drawing ensures that the truss is designed to support the expected loads (also shown on the drawing), that the forces and stresses in the truss do not exceed the allowable strengths of the lumber grade, size and species used, and that the metal connector plates will be of sufficient size to tie together all members and transfer all forces. The drawing is usually computer generated.

Layout plans: Misplacement in complex roof and floor systems may cause geometric problems, such as uneven roofline or ceiling line, or impose a concentrated load in the wrong place. Girder trusses, which support large areas, and drag trusses, which resist earthquake loads, must be placed exactly.

Repair drawings: Authorization from the design engineer is needed before any member can be cut or notched if trusses are damaged at the site or need modification. The truss supplier should provide this.

Bracing instructions: Both temporary and permanentbracing are required on a roof truss system. Temporary bracing holds trusses in place once erected, but before being sheathed. Permanent web bracing as part of the truss design is shown on the engineering drawings.

Tags: Brightly colored tags indicate which webs are to be braced, where the truss is to bear (if not at the ends), and where additional loads frame into the truss. Tags can prevent costly field repairs.

Quality control: Both an in-plant quality control program and "third party" inspections by an inspection agency are required.

Code compliance: Building officials may request documentation of connector plate approval by a major code agency. If required, it should be obtained by the fabricator from the plate manufacturer.

Communication with design professionals: A truss fabricator should discuss a project with the owners and designers before the plans are drawn to better adapt the building to truss use and minimize delays and problems during final construction.

Infornation in this article was contributed by Chris Dudek, chief engineer, Shelter Systems Group. A licensed engineer in 36 states and a member of the Wood Truss Council of America engineering review committee, he has l5 years experience in truss manufacturingeditor.

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