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  1. #1
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    Default Blown Cellulose over fiberglass

    A friend called to ask what I thought about adding blown cellulose on top of his existing fiberglass insulation. I didn't really know what to tell him, so I thought I would post it here. Does anyone have experience or know if this creates any problems, or if it is recommended to pull out the original fiberglass?

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    Jim Robinson
    New Mexico, USA

  2. #2
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    Default Re: Blown Cellulose over fiberglass

    Blown over batt is ok. Make sure that the existhing batts are installed with their vapor barrier (if they have it) towards the house side.

    It's when you put batt over blown that it can be a problem. If you put batt over blown, make sure you use batts that do not have vapor backing on them. If you put batts with barriers over blown, you will trap moisture in the insulation. We all know that is not good.


  3. #3
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: Blown Cellulose over fiberglass

    Cellulose over batt would not be as bad a over blown fiberglass. Over blown fiberglass the weight would compress the blorn fiber and it would no longer have the same R value.

    Thinking of it, it would more than likely have at least a small adverse affect on batt.


  4. #4
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    Default Re: Blown Cellulose over fiberglass

    No problem putting in blown loose fill fiberglass over batt fiberglass, make sure (as John said) the facing on the original batt is down against the ceiling.

    It would be better, though, to put batt over batt with the new batt being unfaced and laid perpendicular to the original batt insulation.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  5. #5
    Ted Menelly's Avatar
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    Default Re: Blown Cellulose over fiberglass

    Quote Originally Posted by Jerry Peck View Post
    No problem putting in blown loose fill fiberglass over batt fiberglass, make sure (as John said) the facing on the original batt is down against the ceiling.

    It would be better, though, to put batt over batt with the new batt being unfaced and laid perpendicular to the original batt insulation.
    You did read cellulose, right?


  6. #6
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    Default Re: Blown Cellulose over fiberglass

    Quote Originally Posted by Ted Menelly View Post
    You did read cellulose, right?
    Nope.

    I would not recommend blown CELLULOSE over fiberglass (batt or blown - post did not say, I went back and checked it).

    I wondered why you mentioned "cellulose" and now I know.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  7. #7
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: Blown Cellulose over fiberglass

    Quote Originally Posted by Jerry Peck View Post
    Nope.

    I would not recommend blown CELLULOSE over fiberglass (batt or blown - post did not say, I went back and checked it).

    I wondered why you mentioned "cellulose" and now I know.
    You schtinking scanner you. I never do that


  8. #8
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    Default Re: Blown Cellulose over fiberglass

    Quote Originally Posted by Ted Menelly View Post
    You schtinking scanner you. I never do that
    Actually, sometimes I do that, but in the case above I did not, and I STILL missed it!

    Jerry, YOU REALLY HAVE TO LEARN TO READ.


    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  9. #9
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    Default Re: Blown Cellulose over fiberglass

    Is the cellulose too wet? Why not over the batts? We could do the unfaced fiberglass batts on top of the original, but blowing in would certainly make things easier. Maybe we look into blowing fiberglass in on top as well.

    Jim Robinson
    New Mexico, USA

  10. #10
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    Default Re: Blown Cellulose over fiberglass

    Not a problem with cellulose being wet, it is just much heavier and tends to settle more than fiberglass.
    The weight of cellulose will compress fiberglass and thus reduce the effective R-value as well as the number of inches. Cellulose base with fiberglass over the top is no problem but cellulose on top gives less desirable results.

    Blown fiberglass would be my choice. Around here I have found having it blown in is about the same price as buying the batts and doing it myself.
    I have a rule, I always pay for a professional job if it is not going to save me money by doing the work myself.
    I am not that fond of sweating and getting covered with itchy insulation!

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  11. #11
    Ted Menelly's Avatar
    Ted Menelly Guest

    Default Re: Blown Cellulose over fiberglass

    Quote Originally Posted by Jim Luttrall View Post
    Not a problem with cellulose being wet, it is just much heavier and tends to settle more than fiberglass.
    The weight of cellulose will compress fiberglass and thus reduce the effective R-value as well as the number of inches. Cellulose base with fiberglass over the top is no problem but cellulose on top gives less desirable results.

    Blown fiberglass would be my choice. Around here I have found having it blown in is about the same price as buying the batts and doing it myself.
    I have a rule, I always pay for a professional job if it is not going to save me money by doing the work myself.
    I am not that fond of sweating and getting covered with itchy insulation!

    I hear that Jim. I just recently help my nephew out in blowing cellulose into his attic. Even though he was in the attic and I was feeding the hoper I was covered with the dusty crap. Not itchy, just dusty and the wind blowing around did not help the situatioon. He could have had someone else do it for slightly more but what the heck, isn't that what uncles are for?


  12. #12
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    Default Re: Blown Cellulose over fiberglass

    That was why I was trying to stay away from the batts myself. I told him I would help, but I was planning on manning the hopper while he crawls around in the attic.

    Jim Robinson
    New Mexico, USA

  13. #13
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    Default Re: Blown Cellulose over fiberglass

    Price it total dollars per square foot and I would be surprised if it actually cost you more than $100 difference between batts material only and blown in turn-key. Maybe I'm just lazy in my old age, but I would not get out of bed without some substantial savings!

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

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