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Q.A client has asked me to build a practical outbuilding with a wood floor system. For simplicity's sake, I'd like to place it on a Sonotube foundation and use continuous-span wood I-joists. The bottom of the I-joists will be about 16 to 24 inches off the ground, and the perimeter joists will be completely protected from the weather by the siding and water table. Is it okay to use I-joists in this situation?

A.Jeff Olson, an engineer with Boise Cascade in White City, Idaho, responds: Although it's always best to consult with your local building official, I know of no limitations on the use of I-joists in this application. Many homes built on pilings in coastal areas have I-joist floor systems; raised pier-and-beam foundations (using either engineered or sawn lumber floor framing) are a popular alternative to concrete slabs all along the Gulf Coast. Keep in mind, however, that floor joists should be no closer than 18 inches to grade, and beams and girders should be no closer than 12 inches to grade. Local jurisdictions may have additional requirements for flood-plain areas.

For more information on raised-floor framing techniques, go to, a Web site sponsored by the Southern Pine Council.