The following article appeared in the Journal of Light Construction magazine. While the main idea of this article relates to the cost efficiency favoring 2x4 over 2x6 walls vs. energy costs, there are other benefits to 2x4 walls. The "Dow™ Intelligent Wall" system that Miracle Homes uses actually costs more than conventional 2x6 walls, but has other benefits.

June 1998 - Journal of Light Construction
Two-by Debate Continues
Thicker is not better, new study finds

A recent study has added fuel to the long-running debate over whether 2x6 exterior walls offer significant advantages over 2x4 walls. Walls framed with 2x6s may be losing out, especially for those willing to sheathe with foam board. As reported in the February 1998 issue of Energy Design Update, increases in wood prices, along with relatively inexpensive fuel and increasing effective insulation are closing the energy performance gap between 4-inch and 6-inch walls.

The article sites a 1997 study done for the Polyisocyanurate Insulation Manufacturers' Association (PIMA) that modeled framing and energy costs for both 2x4 and 2x6 wall construction in a fairly standard 2,000 square foot home in six locations around the country. While the homes with 2x6 exterior walls sheathed with plywood cost an average of $1,907 more to frame than similarly sheathed 2x4 homes (an average of $11,501 as apposed to $9,144 for the 2x4 homes), they saved only about $30 a year in energy costs, even in the coldest climate considered (Minneapolis). At current energy rates, payback time to recover the costs of the fatter studs would be 78 years; even if energy rates rise, payback would be much longer than most consumers are willing to bear.

The more sensible path, the study found, was to use 2x4 exterior walls sheathed with 1-inch foam board instead of plywood. Because this wall breaks the thermal bridging provided by studs, it actually gave a higher effective R-value (18.7 vs. 15.2) than the 2x6 wall, but costs $1,143 less, or about $762 more than a 2x4 wall sheathed in plywood.

For more information, contact PIMA (1001 Pennsylvania Avenue NW, Washington, DC 2004; 202/624-2709; fax 202/628-3856; www.pima.org).

NOTE: The above article uses 1 inch thick foam wall boards as a comparison. Miracle Homes uses 1 ½ inch thick foam wall board which would make the effective R-value approximately 2 R-values higher and increase energy savings even more.