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Net-and-blow cellulose vs fiberglass?

inthestudio | Posted in Energy Efficiency and Durability on

We are finishing a space above our garage, about 26 x 26′, to make a studio, and are trying to keep costs down and still insulate it well. Is the difference in price between the two types justified in improved insulating quality over time or is the actual insulation pretty comparable? The cellulose people are adamant about their product, and the fiberglass people say the difference is negligible. And then how much more/less green are the two? Thank you!

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  1. GBA Editor
    Martin Holladay | | #1

    1. Either type of insulation can perform well. The quality of the installation job (the attention to detail of the installer) matters more than the type of insulation.

    2. No matter what type of insulation you choose, it's important to pay attention to air sealing details. Without a good air barrier, the performance of either product will suffer.

    3. Most green builders have concluded that cellulose is preferable from an environmental standpoint, because it has less embodied energy than fiberglass and a high recycled content.

  2. LucyF | | #2

    We are in the process of building a house and used blown-in cellulose. We had rigorously air sealed before stapling on a membrane to the studs. Then the insulation guys came in and didn't really blow it in to my (extremely high) standards. I don't think they know how to do dense pack cellulose here in my area. The same insulation contractor had to redo some mineral wool batts on a shop we built. his guys weren't great at installing batts either.

    My point is that you have to oversee the work and clearly state what your standards are. Ex. Dense pack cellulose should feel like a firm mattress and is to be installed at a 3.5 pounds per cubic foot so it will not settle in the walls. If you go with fiberglass batts, they have to do a class 1 installation. If you are going with blown-in fiberglass, make sure they know how and have done in many times in the past.

    I would go with cellulose based on low embodied energy in cellulose vs fiberglass. Assuming, of course I could trust them to install it correctly. Absent that, I would install mineral wool batts on my own.

  3. inthestudio | | #3

    Thank you both-- I've read on the GreenBuilding site about how important the installation is, with special attention to sealing all the cracks, etc. Monitoring a couple of guys up in the rafters with spray cans is going to be difficult, but I'll talk to the carpenter who subs them to see if he can keep on top of it. The advantage of keeping animals out makes the cellulose a better choice, but not the 30% additional cost. Patricia, Sudbury MA

  4. inthestudio | | #4

    Hi Lucy-- I'm looking at both; the cellulose is about $1000 more than the fiberglass; I may be able to do a couple of sections in FG and save a little. Or a lot!

  5. Hanley3393 | | #5

    Hi Patricia,

    Cellulose will run you approx 1/4 of the cost more expensive than fiberglass. I agree with Martin and all his points, the quality of installation is key to performance. I work at a insulation company near you (in lowell) and Ill happily stop by if you would like advice or pricing options.
    Jarrod Hanley - InsulKings
    [email protected]

  6. LucyF | | #6

    Patricia, that's exactly the thing to do. Educate your carpenter and he can oversee the air sealing. He does need to know exactly what you expect and the importance. Then he knows what to do on the next job. You help elevate building standards.

    Are you considering fiberglass batts or blown-in insulation? (edit - I meant blown-in fiberglass instead of batts, but I didn't make myself clear.)

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