High-R Wall Construction Strategies: Reducing Costs And Risk While Increasing Energy Performance

by Seul Rhee

The U.S. Department of Energy’s Building America research program has been a source of innovations in residential building energy performance, durability, quality, affordability and comfort for nearly 20 years. This world-class research program partners with industry (including many of the top U.S. homebuilders) to bring cutting-edge innovations and resources to market.

The NAHB Research Center Building America industry team’s high-R wall system research focuses primarily on increasing the wall’s thermal performance and maintaining current constructibility and affordability features. High-R wall system designs for residential construction have centered on reducing the framing factor of the wall system to allow more area for insulation materials. The ultimate goal is to promote options to substantially increase wall insulation by cost-effectively upgrading from 2×4 to 2×6 advanced framing.

The switch to 2×6 framing to encourage use of 24-in. o.c. stud spacing has been an important part of high performance wall system design. A review of lumber use data for home construction indicates that the switch to 2×6 appears to be increasing; however, advanced framing techniques do not appear to be implemented as the increase is primarily with 2×6, 16-in. o.c. framing. The NAHB Research Center recognized this phenomenon, coupled with anecdotal evidence that some builders hesitate to switch to advanced 2×6 framing, and embarked on an effort to achieve a much higher level of optimization when switching to advanced framing designs. This effort was undertaken to minimize the cost increase in switching to advanced 2×6 framing and to increase the wall system’s energy performance level beyond new energy code requirements.

As part of the 2×6 advanced framing, framing might be reduced and insulation increased via an innovative rim header design that uses the rim joist member that is already present in a typical home as a structural member to support and transfer vertical loads around openings. This eliminates the need for structural headers within the wall plane. When combined with 2×6 framing, this advanced detail reduces the framing around openings without increasing the cost of framing materials.

The Home Innovation Research Laboratory (formerly known as the NAHB Research Center) has been conducting research that evaluates the structural performance of rim headers with the goal of increasing opportunities for high-R walls to be used as a much more common construction method. A recent profile summarizes this work and why this particular technology was selected as a 2013 Top Innovation.

Building America has published a Technical Report (High-R Walls for New Construction Structural Performance: Integrated Rim Header Testing) that provides extensive detail on these strategies.

Also, don’t forget that Building America research reports, ENERGY STAR field guides, and a wealth of other technical content are now easily accessible via the Building America Solution Center.