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Closed-cell foam in an unfinished basement in Climate Zone 4/5 (NYC) — 2″ foam — Is it enough?

Darren Finch | Posted in Energy Efficiency and Durability on

Just been given a quote for 2″ CC in our 1480sq ft basement for $1000. I said I didnt want to put any batts etc inside when I frame the walls eventually
Now Martin says R19 for a basement, the installer said “well you lose the dollar/R value, when you go over 2”
I said I wanted 3″ for the R19.
Is it worth the extra, Im tossing it up and siding on Martins side of the more the R value the less heat Id have to put into it but also the fact that the 1st floor floors wont be so cold in winter (there is R19 in the floor joists now)
Any feedback is welcome

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  1. Expert Member
    Dana Dorsett | | #1

    To hit IRC 2012 code min for basements in US climate zone 4 you only need R10 continuous insulation so you'd be good with 2" of ccSPF (R12-ish). In zone 5 it's R15, which would take 2.5". See:

    Your installer is correct that about 17-18 cents per R per square foot the financial payback is somewhere between "long" and "never", depending on current and future energy cost expectations. But that's primarily due to the high cost of closed cell polyurethane foam insulation, which is the most expensive insulation material commonly used.

    But if you used something much cheaper to fatten out the R there is still a financial rationale.for R15 (continuous insulation) or higher. See table 2 p10 of this document (and read the whole first chapter):

    Also note, to do 3" requires spraying it in two lifts with a cooling period between lifts to avoid shrinkage/cracking/fire issues, whereas you can do 2" in a single shot.

    If you did even a 1" shot and insulated the studwall with R15 rock wool batts you'd have a higher performance wall for less money. Given the low framing fractions in a basement wall with just an inch you'd be at about R19 whole-wall (after factoring in the thermal bridging.) An inch of closed cell foam is plenty of protection for the framing from ground water, and sufficient exterior R to protect from wintertime interior air condensation issues at the above grade section with R15 batts in the studwall cavity. With a 1-2"shot if you install the studwall 1" away from the foundation and spray only after the studs are up, which guarantees an inspectable air-tight seal at the stud/foam boundary, eliminating a potential thermal bypass.

    The other thing to consider when using closed cell foam is that it's blown with HFC245fa, which is a potent greenhouse gas (about 1000x CO2), and there's no guarantee that the "extra" inch of taking it to 3" would ever break even from a total environmental hit point of view (from both the polymer and the blowing agent.) It's a great material to use for managing moisture issues, but from strictly an insulation point of view it's one of the least-green options.

  2. Darren Finch | | #2


    Im in Rockland county in NY so Im on the border between Zone 4 &5

    The basement is unfinished so they have the ability to spray around the stacks and sewer pipes, I was going to have to cut and hobble Polyiso around those.

    The framing would be done at some stage so I was thinking for the extra $400 to get me to R19 then I wouldnt need a 2x4 framed wall (to hold the insulation)

    At $47 per R15 60sq ft bag (lowes) of Roxul I would need 25 bags to cover the walls, so for $1100 for the Rock wool) plus say $500 for the 1" CC then at $1600 its cheaper for this guy to do 3" at $1400 he quoted.

    Am I missing anything? The basement wall has waterproofing membrane on the exterior, no foam like they should have.

  3. Expert Member
    Dana Dorsett | | #3

    You have to be a bit careful about insulating between the conditioned space and plumbing & sewer stacks, since during extended cold it can freeze. Better to keep all of that stuff inside of conditioned space.

    This guy is saying he can install 1500' x 3"= 4500 board-feet of closed cell foam for $1400? That's 31 cents-per board-foot which is less than a third of the pricing I've been seeing. Is he having a 70% off sale?

    In my neighborhood 39cents/board-foot would be about the price for half-pound open cell foam (which you really shouldn't use on foundation walls.) For 4500 board-feet of 2lb foam $1400 might not even cover his cost. Something doesn't seem quite right here. (Even $4K would be a deal on that much 2lb foam.)

  4. Darren Finch | | #4

    I know, when he quoted me the price it was cheaper than be buying seconds polyiso of the same thickness (the killer for polyiso seconds/reclaimed is that none of the large guys like insulationdepot are near me so freight was 800 which was the reason I started to look elsewhere

    Am I calculating it correctly, foundation wall to wall is 47.5 by 31, I dont need the rim joists done because Ive already blocked and sealed them with 2" xps dow

    admittedly this an over the phone quote and I asked twice to ensure it was CC.

    I will call again to ensure the price was right and get them to check everything to ensure its correct
    These are the people so Im not sure what other questions I should be asking them also, as I want to make sure this is done right the first time

  5. Expert Member
    Dana Dorsett | | #5

    Maybe you should ask them for a budgetary quote on 4500 board-feet of 2lb foam, and find out whose chemistry they are using, and for any references close to you that you might be able to inspect (or at least talk to the client.)

  6. GBA Editor
    Martin Holladay | | #6

    Who is this guy Martin, and where is it that he advised you to insulate your basement to R-19?

  7. Darren Finch | | #7

    So I contacted this same company through their web site pretending to be someone else and got a price for the 4500 bd ft of $3500
    So Im not sure what the person thought I said to get such a low price or whether they were just going to use open cell, say it was closed cell and just take the money and run
    So can I go with open cell and add the Roxul batts to bring it up to the R19, or just do the 1" and batts as you initially suggested
    The basement is dry, sealed externally by a blue/green water membrane so do I need the closed cell ?

  8. Darren Finch | | #8

    Martin, the Martin is you
    Sorry I read one of your other posts wrong that Zone 5 basements should now be R19.

    I was planning to use foil faced 3" polyiso to get the R19, so sorry that is an error on my behalf.

    My plan was to go the 3" Polyiso (R19) so I could use a 2x2 wall framing as I wouldnt want to use cellulose/batts for the basement and the need to heat or cool would be that much lower.

    I apologize for my mistake, Dana's document above shows R15 is what is needed

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