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Thread: Insulation question - rigid & spray foam hybrid

  1. #1
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    Insulation question - rigid & spray foam hybrid

    I'm in the early planning stages of remodeling our bedroom and and looking into my insulation options.

    The house is a cape style build in the late '40's. There is some existing fiberglass insulation (maybe 1/4" -- but it has a neat leopard print backing ) that I'm probably going to remove & replace.

    I would like to go with spray foam insulation, but the size of the project is an issue. I've used it in other areas of the house and I've been very happy with the results.

    It is a bit too small to make it cost-effective to hire it out -- the contractor that did my basement tells me there is a base "set-up" fee and then a cost per board foot. Its a bit too big of a project for the DIY kits (used them before, they are surprisingly easy to work with).

    So I got to thinking -- what about using rigid foam boards to fill the bulk of the cavity and use the DIY the spray foam to seal everything in place. The rigid boards cost less than half of the DIY spray foam kits, so I'd save some $$$.

    Anyone have any experience with this?

    Thanks,
    Matt

  2. #2
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    Question you have to ask your self. Is the few dollars I save now going to be floating through my wall for the rest of the time I live in this house?
    It could be worse You could be on fire.
    Stupid hurts.

  3. #3
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    Quote Originally Posted by Chuck Thoits View Post
    Question you have to ask your self. Is the few dollars I save now going to be floating through my wall for the rest of the time I live in this house?
    Hi Chuck,

    That's part of what I can't figure out.

    The rigid foam (R5 / inch) has a comparable R value to the spray-in stuff (6-7 / inch), so I don't think I'll be sacrificing much on that front. I'd expect the cost recovery on a delta of 2 to 4 R to be quite long.

    Since I'd be putting on an inch or so of spray foam over the foam boards, my expectation/hope is I'll get comparable performance for air sealing as if I used a full 4" of spray foam. Is this a reasonable performance expectation? Or is there something obvious I'm missing here?

  4. #4
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    The only thing I see is what foam board you use open or close cell?
    If you use an open cell foam board your going to have to spray 2" of closed cell on the inside of it to get your vapor barrier.
    It could be worse You could be on fire.
    Stupid hurts.

  5. #5
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    Quote Originally Posted by Chuck Thoits View Post
    The only thing I see is what foam board you use open or close cell?
    If you use an open cell foam board your going to have to spray 2" of closed cell on the inside of it to get your vapor barrier.
    Thanks for the insight -- I hadn't thought about issues with mixing open & closed cell foam. I'll have to check what the pink boards the local borg carries are made of.

  6. #6
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    I'm no expert by any means on this, but i do know that every house we've built in the last few years, has had open cell on all exter walls and ceilings. As far as your idea i don't see why it woun't work.They tell me that using closed cell on exter walls will rot out your walls. No vapor barrier needed at least that's what they say down here in the south. So if you can maybe talk to someone in your area they should be able to help more then me.
    Steve

  7. #7
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    Quote Originally Posted by Stephen Bellinger View Post
    I'm no expert by any means on this, but i do know that every house we've built in the last few years, has had open cell on all exter walls and ceilings. As far as your idea i don't see why it woun't work.They tell me that using closed cell on exter walls will rot out your walls. No vapor barrier needed at least that's what they say down here in the south. So if you can maybe talk to someone in your area they should be able to help more then me.
    Steve
    Funny just a few hundred miles north they say to use only closed cell cause open cell will rot your walls and you must have a vapor barrier.
    It could be worse You could be on fire.
    Stupid hurts.

  8. #8
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    Quote Originally Posted by Chuck Thoits View Post
    Funny just a few hundred miles north they say to use only closed cell cause open cell will rot your walls and you must have a vapor barrier.
    That sounds about right. I don't think it's been out long enough to really know. I do know that David Keller just put it in his shop out in Oak. After asking him about it, and telling him the little bit i know. He talked to his guy out there that was doing it and they told him open cell is the only way.

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