Many builders wrestle with how to best insulate basements. Interior stud walls are time consuming to build. Exterior foam invites termites to tunnel into the house, and can fall victim to the ravages of ultraviolet light and the teeth of the neighborhood dog. Lightweight insulating blocks, which use air, fly ash, or polystyrene beads to boost their R-values, lack the strength and water-resistance of standard concrete. Despite these obstacles, researchers at Oak Ridge National Laboratory recently set the unlikely goal of designing an affordable foundation with the strength of traditional concrete and up to 50 percent fly ash or other low-density additives. They seem to have succeeded.

The system, which will be licensed to manufacturers, uses interlocking dovetails to bind structural outer blocks to lightweight, insulating inner blocks. Vertical and horizontal reinforcing rods help stiffen the wall while pinning it to preformed footer blocks. According to Jeff Christian, the researcher who headed the project, the system's R-6 to R-8 insulating values should satisfy most energy codes in the middle to southern U.S. Expanded polystyrene inserts can raise the insulating value to R-15.

Christian expects costs to be competitive with a standard masonry wall with interior insulation. The system is also easy to use. Skilled masons are needed to lay the footers, but the wall blocks can be slipped together by anyone. In fact, Christian has fielded inquiries from Habitat for Humanity and other groups that routinely build low-income homes with unskilled labor.

Contact: Jeff Christian, Oak Ridge National Laboratory, 423-574-5207