Jesse Lizer’s plans for a new house in Climate Zone 6 call for a 60-foot long walkout basement wall on the north side. The three below-grade foundation walls will be built with insulated concrete forms (ICFs) with an R-value of roughly R-25.
Lizer’s question, posted in GBA’s Q&A forum, concerns the exposed north wall of the foundation. Should it be built from ICFs like the rest of the foundation, or would he be better off framing it as a double-stud wall with an R-value of 40, like the rest of the house?
With the wood-framed wall, he not only gets better thermal performance, but wood framing would also make it easier to put in windows and doors. “Plus,” he adds, “if a rough opening gets framed wrong or something changes, we are fixing wood and not concrete.”
“Would it still make a better/stronger basement system if all the walls were ICF?” he asks. “I realize the length is quite long, which is why I am curious if it would even help make any difference or not.”
The discussion is the topic for this week’s Q&A Spotlight.
Thermal mass vs. higher R-value
With a core of concrete, the ICF wall has more mass than a wood-framed wall, and Mike Collignon thinks this benefit is worth considering. “This often doesn’t show up in R-value discussions,” he writes, “but it [is] quantifiable and does make a difference in reducing air infiltration.”
Added thermal mass, however, may not have much benefit in Lizer’s climate zone, Dick Russell says.
“Bear in mind that the ‘thermal mass’ effect of concrete is most useful in climates where there is a…