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ICF in colder, more variable climates

Whethernut | Posted in Green Products and Materials on

I lived in an ICF home in TN that had equal thickness foam either side of the concrete-rebar core.  This resulted in daytime heat working into the building late at night shifting the air conditioning run times mostly to the wee hours.  Probably just as well since less temperature difference outside compared to desired inside temperatures.  In the winter though, heat lost at night meant longer, cooler startups after dawn.  Does anyone make ICF forms that have extra foam on the exterior side and less on the interior side for more appropriate heat transfer and storage?  Or, has anyone tried gluing exra foam on the exterior side of the ICF?  How’d that work?

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  1. jackofalltrades777 | | #1

    Numerous studies were done on the placement of EPS and whether or not having extra foam on the outside or leaving the interior concrete exposed provides any benefits.

    The conclusions:
    EPS insulation placement doesn’t seem to be a major factor in the effectiveness of the thermal mass in ICF's. The Association tested different wall configurations in 25 different climates and found that, even with the concrete encapsulated in the foam, there’s a still thermal mass effect. “A [high-mass] system with lots of insulation will out-perform one with less insulation, regardless of where the concrete and insulation are placed.”

    Greg Kallio, a professor of mechanical engineering at California State University in Chico who specializes in heat transfer, recently tested this theory by modeling “the whole gamut” of wall systems, from stick-built to SIPs to insulated concrete, using industry standard energy analysis programs like EnergyPlus, as well as his own custom software. His conclusion? “The effectiveness of thermal mass is very dependent on diurnal temperature variation. You want nighttime temperatures that get at least 10 degrees cooler than the thermostat set point. If you keep the thermostat at 78, outside temperatures need to fall below 70 degrees at night to really take advantage of the thermal mass.”

    Oak Ridge National Laboratory stated that, “A mass wall might be 3 times more effective in Phoenix than the baseline you would expect from the insulation alone, but in Minneapolis it will still be 1.5 times more effective than the baseline. There, an insulated concrete wall with a material value of R-11 could have the same heating and cooling loads as a wood-framed wall insulated to R-20.”

    The law of diminishing returns comes into play. The expense of adding more EPS to the ICF begins to take over. Most ICFs have 2.5" of EPS on both sides of the concrete core (typically 6"). Adding more EPS to the exterior will result in very little ROI.

    Here is a very detailed scientific study:

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