To improve thermal performance of her townhome development “City Cabins” while keeping material and labor costs to a minimum, builder Martha Rose devised a “plywood-over-foam” wall assembly designed to provide greater insulation, air sealing and thermal break. With her engineer’s stamp, City of Seattle and Shoreline have accepted her innovative design numerous times through prescriptive code compliance.
For this 5-unit entry-level, zero-net-energy subdivision in Washington County, Oregon, the builder used an innovative “Thermal Break Shear” (TBS) wall assembly with rigid foam insulation between the lumber framing and plywood sheathing in an otherwise conventional light-frame wall assembly. The Code Official required proof the proposed shear wall assembly would be capable to resist code level seismic forces, so the builder contracted with Oregon State University to perform destructive seismic testing, which demonstrated not only that the assembly complies with structural code, but surprisingly, TBS wall is significantly more resilient in an earthquake than a conventional wall.