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jhoin | Posted in Energy Efficiency and Durability on

I have a 1950’s ranch style house with what appears to be a botched insulation job in which fiberglass was blown in the walls. During some renovation work a couple years ago I discovered that the 4inch wall cavities were only filled to about 40-50%. I would like to redo the insulation with something that I know will fill in the entire wall cavities. I once considered airkrete, but have been unable to find an installer in our area (Kalamazoo, MI). The “Retrofoam” product has recently come to my attention and it seems to have a lot of characteristics that I like such as it is a foam, it will expand to fill the cavity, and it has a decent R value. I talked with the installer and he said that it is an open foam product which worries me a bit since it won’t provide an air barrier. It also shrinks and provides an air space along the studs that is equivalent to a fiberglass batt installation. My questions:

1) Does anyone have any experience with Retrofoam? If so, how well does it perform.

2) I will eventually install 4 inches of foam on the exterior of my house, will this have any adverse effects on a Retrofoam installation?

3) If there is already fiberglass batts in the cavity, how much will the R-value be affected by the Retrofoam installation, i.e., will the remaining thickness of fiberglass have a significantly reduced r-value. For example will 4 inches of fiberglass smushed down to 1 inch still have an insulating value of 3.5 for that 1 inch?

Thanks for your help in advance.

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Will 4 inches of fiberglass smushed down to 1 inch still have an insulating value of 3.5 for that 1 inch?"

    A. No. Its R-value will be greatly reduced.

  2. davidmeiland | | #2

    I've done some thermal imaging of a building where Tripolymer 105 was installed into empty stud bays. My observation--never confirmed by actually opening a wall--is that the foam appears to have slight variations in R value throughout, with some areas missing entirely, such as the very tops of wall cavities and the areas directly under windows. My sense is that it's hard to install completely, hard to know if/when the bay is as full as you can make it, and hard to inject to the very top of a bay.

    Other than that... no experience.

    Seems to me that if you foamed your stud bays now and then foam-sheathed your exterior later, you'd have a vulnerable assembly. Depends partly on the perm rating and thicknesses of the products, of course. Since the injection foams do not have a particularly high R value, why not get the FG out and install dense packed cellulose in the walls? You could then install foam sheathing later with no issues.

  3. bdrfab | | #3

    Not really answering your question, however, you may find to be a good resource for finding an installer in your area. Personally I am in the same (slow) process as David suggests, also with 4" of foam being installed. As a point of clarification, are there batts in the wall or is it blown in fiberglass?

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