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Community and Q&A

Injected foam insulation

Q4P5JdZ2mc | Posted in Energy Efficiency and Durability on

I am trying to get some ball park about injectable core foam for hollow concrete blocks.

I have an existing home in South Fl houses faces east and west. I am considering having the walls filled with inject able core foam. The only insulation that I think is in the walls is the brown paper with foil on back. The house is CBS built in 2001.

I really know nothing about this and finding that no one talks in layman’s terms about this. I found the R rating of hollow block to be 1.7 to 2.9 so with that in mind approximately what would be the R values with these blocks filled with foam? I understand windows and opening will cause loss but just trying to get idea on just the block 1.7 vs ?

Some say R14 some say R 40 depends if open cell or closed cell?
I would like so unbiased opinion please.

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  1. Riversong | | #1


    Since the concrete webs of the hollow blocks act as thermal bridges, regardless of what fills the cores, you're not going to get the R-values you've been quoted.

    Depending on concrete density, a hollow 8" block wall will have an R-value of 2.92 to 2.06. With foam-filled cores (R-5/inch), the wall R-value will increase to 4.97 to 11.27 (average 8.12).

    If you want better insulation, you'll need to install a thermal break, like interior rigid foam board. If you use foil-faced polyisocyanurate foam, then strap and drywall, you'll have a more efficient wall than by filling the cores, and you'll reduce condensation and moisture diffusion.

  2. jklingel | | #2

    Robert: Slightly different topic. Isn't it best to keep the block on the inside of the foam (except, perhaps, in houses that are already built, as that may cause real issues w/ windows, etc.) thanks. j

  3. Kevin Dickson | | #3

    Injectable foam from the kits can be found for about $1/board foot, which is $12/cubic foot.

  4. Riversong | | #4


    The poster was asking about an existing home, and "best" depends on what the goals are.

    Insulating a concrete (block or poured) foundation on the outside keeps the thermal mass where it belongs - adjacent to the conditioned space. But that requires flashing and protecting the exterior foam from insects, UV and physical damage - and ideally designing the structure so that the wall plate covers the foam board for continuity of drainage plane (and aesthetics).

    But, if the basement is going to be finished conditioned space, then it may be easier to waterproof the block on the outside and insulate, strap and finish on the inside. Isolating the concrete from the living space reduces the issue of moisture wicking up a below-grade wall that doesn't have a capillary break between it and the footing (how many do?) getting into the living space.

    There's more than one way to feed a cat (it's no longer politically correct to skin a cat).

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