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 HomeBuilders uses actually
costs more than conventional 2x6 walls, but has other benefits.
- Journal of Light Construction
Thicker is not better, new study finds
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.
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.
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.
information, contact PIMA (1001 Pennsylvania Avenue NW, Washington,
DC 2004; 202/624-2709; fax 202/628-3856; www.pima.org).
The above article uses 1 inch thick foam wall boards as a
comparison. Miracle HomeBuilders 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.