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Thread: Roof Insulation

  1. #1

    Default Roof Insulation

    Hello everyone...

    Currently I am building a small office/studio/gym in northern Florida where it is hot and humid about 8 months out of the year.

    This building has a precise east/west orientation with a shed roof and 2' overhangs on all sides. The roof slopes downward from north to south. I am planning to insulate it with spray foam. The company is saying they'll spray 5" of open cell foam which will be about R19. They also say that is equal to R30 fiberglass. I am concerned about this and would appreciate any thoughts you might have.

    Another question is would I get any benefit from insulating the overhangs? The south overhang will shade the south facing wall throughout the summer months. Some have said the overhang makes no difference, but I'm having trouble believing that if the sun is effectively blocked at the roof level the walls will be cooler if no radiant heat transfers through the overhangs.

    Any thoughts you may have regarding this would be greatly appreciated.

    Thanks,
    elgin

  2. #2

    Default Re: Roof Insulation

    Elgin,
    If you hire an insulation contractor to install R-19, that's all you will get. You certainly won't be getting R-30 (the minimum code requirement).

    This is an old story. Read about it here:
    http://www.greenbuildingadvisor.com/...n-icynene-says

  3. #3

    Default Re: Roof Insulation

    I would make sure the foam will last and not dry out and break apart...then you will be back insulation again...You need to find out the warranty with the company to make sure you are not replacing in a couple of year...www.roofingsanrafael.org

  4. #4
    Join Date
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    Houston & Washington Texas
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    Default Re: Roof Insulation

    Quote Originally Posted by elgin?s View Post
    The company is saying they'll spray 5" of open cell foam which will be about R19. They also say that is equal to R30 fiberglass. I am concerned about this and would appreciate any thoughts you might have.
    In a hot-humid climate homes with 5"-6" of spray foam in rafters and walls will perform much better than R-19 fiberglass in the walls and R-30 fiberglass in attics. I have several new homes built in the last 5-6 years to prove that.
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  5. #5
    Join Date
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    Default Re: Roof Insulation

    Allan, have you used 5" to 6" of open cell in the ceilings?
    Or did you opt for closed cell?

  6. #6
    Join Date
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    Boston, MA
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    Default Re: Roof Insulation

    They pretty much reject anything less than R38 around her. The honeymoon is over for SPF. Don't matter what material it is, it's got to be R38.
    "First we finish the game, then we’ll deal with the Armada!"

    Sir Frances Drake

  7. #7

    Default Re: Roof Insulation

    Thank you for all your responses.
    Last edited by elgin?s; 06-27-2014 at 07:46 AM.

  8. #8
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    Default Re: Roof Insulation

    I could get away with less than r38 in a lot of localities and have tried it in several. it appears to work good. Have not dared to try the open cell on the ceiling yet. But from what I have read here, it sounds like OC would work as long as the interior is kept less than ridiculously humid(heating zone).

    One thing I am sure of is that the code requirement for insulation values is arbitrary and capricious. So I don't put any stock in the code if I can get away with it. The problem is that there are no unbiased science guys to tell us what a prudent r value would be. So we have to rely on experience. I would put a lot of stock in Allan's examples. But you still never know if another inch would be worth it or not.

    A layman can look at a graph and see that it doesn't take many r's to keep in/out most of the heat/cold. But controlling the surface temperatures takes more r's and there effects on comfort are not as easily understood.

  9. #9
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    Default Re: Roof Insulation

    Quote Originally Posted by johnny watt View Post
    Allan, have you used 5" to 6" of open cell in the ceilings?
    Or did you opt for closed cell?
    We use open cell. Except for wine rooms where we use closed cell.

  10. #10
    Join Date
    Aug 2009
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    OrangeCounty California.
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    Default Re: Roof Insulation

    I would like to kow how it is that a company will tell someone that they will install insulation of any kind at R-19 then it somehow magically turns to R-30.

    R value either is a certain value or it is not.

    Andy.
    Was a GC, doing drafting & design now.
    www.draftinginoc.com

  11. #11

    Default Re: Roof Insulation

    Never really heard of foam going from a R-19 to a R32 by just spraying it unless they are spraying to much causing a R32...Interesting have to talk to friends about this one...

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