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Community and Q&A

Swapping in open-cell for cellulose

ranson | Posted in Energy Efficiency and Durability on


I appear to live in an area with not too many contractors who do dense pack cellulose in new construction. (A fair number of guys to wet spray.) I’m looking to build a double wall house. While I’ve got a lead on dense pack installers, there are a lot more guys who are suggesting water-blown open cell.

Is water-blown open cell insulation is acceptable in a Zone 5, 12″ double wall cavity with an external plywood air barrier. Are there hygrothermal downsides to this subsititution, other than the change in R-value/inch?

I get that cellulose from recycled feedstock is environmentally superior, but I have to adjust to the local skillset.

Thanks for any help!


Brockport, NY

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  1. Expert Member
    Dana Dorsett | | #1

    This wall is VERY similar to what Carter Scott designs and builds (usually in the cold-edge of zone 5A), though his sheathing is usually OSB rather than CDX. CDX is more vapor permeable when wet than OSB, and would most likely have lower peak and average moisture content. See:

  2. Stockwell | | #2


    I am building a home with staggered 2 x 4 studs on 2x8's in Zone 4. I originally asked for 2.5" of closed cell and the rest dense pack cellulose. It turned out to be far cheaper to replace the cellulose with open cell foam. I added the closed cell to end any concerns about moisture content rising too high in my external sheathing.

  3. Expert Member
    Dana Dorsett | | #3

    Kevin: By adding the 2.5" of closed cell foam on the inside of the sheathing you may have increased the average moisture content of the sheathing in a zone 4 climate by pretty much blocking it's ability to dry toward the interior. The exterior moisture drives are significant too.

    Hiring an engineer to run a WUFI on the wall stackup to find out if it was necessary or counter-productive would have been cheaper than the cost difference of 2.5" of closed cell foam vs. filling that 2.5" with open cell.

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