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Why do most contractors prefer fiberglass over cellulose? And some other questions.

greendiy | Posted in General Questions on

I’m in Sacramento area in Northern California. I have been looking into putting more insulation in my attic. The house was built in early 90s and has batt and fiberglass insulation, but I think it will be better to have more. I’ve been asking around contractors but all but one was doing only fiberglass. It seems like cellulose is better in many aspects but I wonder why contractors in my area hate it. The dust issue in cellulose installation is messy enough to scare them away?Green Fiber also has poorer ratings than Atticat in Home Depot and Lowes. Is it just marketing or reflects real issues with cellulose?

I’m leaning towards doing it myself, thinking that nobody would pay attention to every corners in my tight attic to do air sealing as if it’s his/her own house and that I can do cellulose. It won’t be easy but doable. I see a lot of complaints of a free blow-in equipment that comes with cellulose purchase at Home Depot or Lowes. Is it still true? Unlike the atticat fiberglass machine, the cellulose one doesn’t seem to have a switch at the end of flexible pipe and I wonder how to coordinate the communication easily with someone in the attic and some in the garage with the equipment.

In my local Home Depot stores, they sell only two cellulose products, Green Fiber and TAP. Green Fiber seems to be more popular but TAP argues that they are better in controlling bugs and rodents. I wonder if you could advise me what to buy and any way to buy them cheap.

I do have some but not serious rodent droppings in the attic. Can I just leave them there and put cellulose over it? I am going to put some bleach over and put cellulose over.


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  1. user-6623302 | | #1

    I have done blown-in several times. If you are handy just do it. have used blowers from HD and Lowes. A tool rental place may have better equipment. The machines from Big Box are going to vary from store to store. Shop around. I think the ones I used had an installer cut off switch. If you want cellulose, find a wholesale outlet and get names of customs. Does CA have energy programs that can get you a discount/rebate?

    1. greendiy | | #4

      Thanks! The $3k rebate available through the electric utility SMUD is available but only through a sort of certified contractor. It requires certain conditions like replacing old ducts with insulated ones, burying them under blow-in insulation, air sealing, and some tests of verifying the work. Even with the rebate, the additional cost is like $5-9k. The main difference among them is that some say they have to remove old insulation but some say they don’t have to. If I do attic sealing and insulation myself, I can do it around $1k. So, I can’t justify the additional costs despite the nice replacement of ducts and others.

      1. Expert Member
        BILL WICHERS | | #6

        You could remove the old insulation and air seal yourself, then have a contractor come in to do the insulating work so that you could get the rebate. Save money doing the labor intensive work yourself, then get the rebate on the more materials intensive insulation installation.


        1. greendiy | | #8

          Thanks for the suggestion and I will see if I can find any contractor who can work with me like you suggested.

  2. Andrew_C | | #2

    You kind of glossed over the distinction, but air sealing is a totally different job than insulating. It's more important, and it needs to be done before the extra insulation is put in, regardless of which product you choose and who installs it. You may know this, but it wasn't clear to me from your post.

    1. greendiy | | #5

      Air sealing is one of the reasons why I want to do it myself. I crawled around my tight attics, and I can’t believe most contractors would take time getting things done right. I’ll not be as professional as contractors but I can take time to do it as best as I can as it’s my house.

  3. Expert Member
    BILL WICHERS | | #3

    Fiberglass' main advantages are that it is lighter weight per unit R value, and it can 'dry out' if it gets wet -- cellulose usually needs to be replaced if it gets significantly wet. Cellulose's main advantages are that it holds it's R value better under all conditions (it's more resistant to convective air flow, for example, and IR warming up the upper layers in an attic), and it's better and "sealing" any small air leaks that you missed with your initial air sealing efforts.

    I say "sealing" because cellulose IS NOT AN AIR BARRIER. You still need to do a proper air sealing job prior to putting in blown cellulose. No exceptions here! Do a conventional job of air sealing with caulk and canned foam prior to insulating and you'll have much better overall results.

    BTW, loose fill cellulose and loose fill fiberglass are both dusty during installation. I recommend a "real" respirator -- the kind with a rubber mask and canister-type filters -- since those are much better at sealing to your face which greatly reduces how much of the dust sneaks past the filters and gets into YOU.


    1. greendiy | | #7

      Thanks for the advice. I’ll buy a full face mask with high efficiency particulate filters!

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