Wall thickness can vary from 8 to 15 inches, depending on the particular product and the amount of insulation used, but the wall will be wider than a SIP or stick-framed wall with a comparable R-value.
What’s the payoff ? Solidity, for one thing. Reinforced concrete stands up well to high winds, so it’s an asset in places like Florida and the Gulf Coast. The sheer mass of a concrete wall--and a cast-in-place wall, in particular--will deaden street noise, making the home quieter inside than a wood frame. Concrete also doesn’t catch fire or get eaten by termites.
CWS manufacturers also make claims about energy savings, but some industry experts say that the R-value numbers alone aren’t overly impressive. A study by Building Science Corporation in Westford, Mass. points out that the R-20 offered by a 15”.-thick ICF wall with 5” of EPS would not be considered high in northern climates and “would need to be supplemented by interior insulated frame walls, which further raises the cost.” On the plus side, they add that the whole wall R-value of a properly detailed ICF wall will be much closer to its nominal value than with a stick-framed wall, largely because of the lack of thermal bridging.
Thermal Mass and Climate
Masonry wall advocates counter that R-value isn’t the whole story because concrete offers an added benefit that wood framing doesn’t: thermal mass, or the ability to store heat. Because masonry is slow to respond to changes in outdoor temperatures (see Graph 1), temperatures in the house stay more even, easing the load on the HVAC system.
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