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Climate Zone 7 ICF thickness vs EPS thickness

sleaton | Posted in Energy Efficiency and Durability on

I am building in Sitka, AK.  The temps there remain at 50 degrees F almost year round, they can hit 65 ish in 1-2 months in the year.

Given the constant mild winter conditions of this location I am pondering two differences in building with ICF.

Is an 8in ICF wall going to outperform a 6in ICF wall ?  I am thinking where you don’t get the exterior heat and thermal boost that I it will be negligiable.  I am thinking my money might be better spent on a form with thicker ICF insulation rather than more concrete.   Thoughts ?

Also there are forms that for example have 2in EPS on one side, 4 on the other.  Would the thicker side be best outside ?

Thanks in Advance, I have been reading study after study and the FEWF papers, but I haven’t found what I am looking for.

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  1. sleaton | | #1

    This is the closest I have found. Where the assembly mass and wall does perform better, the interior and exterior mass temperatures don't lead me to believe that the Mass is near as important as the ICF insulation thickness. So I am thinking a thinner width concrete wall with more EPS insulation is where I am leaning.

  2. Expert Member
    Michael Maines | | #2

    In almost all cases, insulation will outperform thermal mass. There are some exceptions but not where the temperature is relatively constant. I would go for the extra insulation and reduce the concrete, which also has a very high global warming impact. Depending on the details it probably doesn't even matter on which side of the concrete you put the extra insulation.

    In fact, because of the global warming impact, I would never build a house with ICF walls, except possibly below grade in some situations. But that's not what you were asking about.

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