Q. When building a super-insulated house, one of the ways to increase insulation levels in the wall assembly is to increase the thickness of the wall. But instead of using double-wall framing, would it be okay to frame walls with I-joists?
A. Gary Schweizer, P.E., a senior engineer with iLevel by Weyerhaeuser in Charlotte, N.C., responds: Yes, I-joists can be used to build walls. You’ll probably need engineering assistance to help with the design, since specific application guidelines and details haven’t been developed by the I-joist industry or adopted by any building codes. Tall walls and high-wind or seismic locations will require engineering to ensure the lateral stability of the I-joist flanges, which under normal conditions could be provided by exterior sheathing and interior drywall. Engineered solutions will be required when wall framing exceeds certain heights, too.
You’ll also need to provide full-depth bottom and top plates to ensure even vertical loading. Since the majority of compression forces are distributed to the flanges, a 9½-inch I-joist will require 9½-inch-wide plates so that both flanges have full bearing. In addition, the bottom and top ends of the I-joist will require web stiffeners or end blocking to help with vertical load transfer and with the lateral connections with the plates. Intermediate I-joist blocking may also be required for fire stopping and installation stability.
