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Spray foam contractors

Quinton Bryant | Posted in Energy Efficiency and Durability on

Why do all the spray foam contractors I call tell me 5.5-6 inches of open cell is all I need.
Code here is r38 zone 3.I know there’s a article on it but I’m jot kidding,every one said the same thing,5.5-6 inches is equal to around r40.

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Quinton,
    It's possible to achieve almost R-40 with 6 inches of closed-cell spray foam, but not with 6 inches of open-cell spray foam. With open-cell spray foam, 6 inches is more like R-22, not R-40.

    For more information on the topic, see It’s OK to Skimp On Insulation, Icynene Says.

  2. D Dorsett | | #2

    They say that for a couple of reasons:

    *For starters 5.5-6" is the maximum that can be safely sprayed in one lift, and they don't want to hold up the crew for hours waiting for the foam to cool enough to spray the next lift.

    *At the comparatively high $/R of foam compared to fiber insulation the financial payoff for the next 5-6" is much longer than the initial 5-6"

    *Don't discount the wealth of ignorance out there, reinforced by long standing industry lore (rather than measured performance.) A lot of them actually believe their own BS, because that's what they've always been told.

  3. Alan B | | #3

    "Don't discount the wealth of ignorance out there, reinforced by long standing industry lore (rather than measured performance.) A lot of them actually believe their own BS, because that's what they've always been told."
    I LOLed, you can say that again.

    The OP does not have to only use spray foam, a few inches with the remainder done with cellulose is a good option.

  4. Coop Mag | | #4

    I ran into the same thing. I'm in zone 4 and ran the numbers through a simple energy analysis. Going from R20 to R35 was an annual savings of probably around $80 a year. The additional cost to go to r-35 is $1,000 in my case.

  5. User avatar
    Dana Dorsett | | #5

    C.Maglio: So, $80 / year in after-tax savings on a $1000 is investment is an 8% after-tax return.

    How much would you net putting that $1000 in bank CDs, Treasury bills or other similarly safe places?

    It may or may not raise the resale value of the house by $1000, assuming you're going to be moving out in short years, before it "pays off", but it won't hurt the resale value the way being substantially sub-code might, particularly if there is any chance of energy price inflation between now and the time it goes on the market.

    But if you can get the same $80 / year energy cost savings with cellulose or fiberglass for $500 or less for a 16% or better ROI, why spend the "extra" $500+?

    All-foam solutions don't always make the best financial sense, since it comes at a premium cost. But at current energy pricing it's usually "worth" going considerably more than 5-6" in a zone 4 roof on a lifecycle basis even at the higher cost.

  6. Coop Mag | | #6

    Dana, You are correct which is why I'm paying to have the extra sprayed. I have ducts and other equipment in the attic. Spayfoam just seemed easier than other methods.

  7. John Clark | | #7

    Maybe get away with less foam in the ceiling if you go un-vented attic and apply it to the underside of the roof decking? Martin would have a better grasp of this.

  8. User avatar GBA Editor
    Martin Holladay | | #8

    Chris,
    In most cases, the situation is the opposite of the one you describe.

    It's usually easier to do a vented (unconditioned) attic without foam than it is to do an unvented (conditioned) attic without foam.

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