Shop Attic blow in insulation

Rick(MN) · Nov 29, 2009

Getting close to ready to blow the insulation in the attic of my shop. From what I understand, both cellulose and fiberglass have their advantages and disadvantages. I also am under the impression that cellolose settles more than fiberglass. Can someone tell me the rate of settling for the 2 products so I can determine the amount to "overfill" to still have the insulation value I want 10 and 20 years down the line? Any other thoughs or experiences with with either product would be appreciated as well.

Joe in Neb · Nov 29, 2009

I have a metal ceiling and I had to use fiberglass blowin because celulose voided the warranty. Also when I did mine a builder friend of mine advised me to get some professional quotes as well. I ended up having a professional come and do the whole job in one day that would have taken me at least 3. The bill was only 50$ more than I could have bought the insulation and done myself. He got much better discount on insulation than I did. I put in a R48 and I keep building at 68 and heat runs maybe 5 min twice a hour

fixerupper · Nov 29, 2009

My shop attic is 30'X32' with a metal roof. The shop ceiling is plywood. When the shop was built in 1982 I blew in 12" of cellulose and now after 27 years it's down to 5". I was up there the other day and after I scanned the attic I wondered what I should do now! I'm in NW Iowa and we get a lot of sweat off our steel roofs, so now there are deep drip lines under the perlins. Under the ridge vent the insulation is really matted down. There is no protection to the north and west so the snow really gets a crack at the north side of the roof. The ridge line goes east-west. A sheet of some kind of insulation under the steel roof would have helped me a lot.

The cellulose insulation in my house attic has been there longer than the shop insulation and it is still fluffy under the wooden roof so the steel shop roof was definitely the culprit. I kind of think blown in fiberglass would have been a better choice, but as far as I know it wasn't available in this area at the time the shop was built.Jim

BCnT · Nov 29, 2009

i just had my attic blown with cellulose over fiber batts...main reason i went with it over fiber is itch factor if i have to do work in attic on wiring/etc.
cost me $660. this spring to have 1200 sq ft upgraded to R-30 from 3.5" batts.

msb · Nov 29, 2009

I blew in fiberglass(r38) on top of a metal ceiling. Would have had to use visqueen vapor barrier if I had used cellulose. Got it from Menards

MSD · Nov 29, 2009

In new home construction we have used both. The problem we found with fiberglass is the air infiltration. Any recessed lights on a cold windy day felt like having a window open so we had to wrap them with blanket insulation before blowing the fibeglass. Also, any water drips right on through the fiberglass. I've been in an atttic when somebody came in and slammed a door a little hard and you could see the whole ceiling drop. We have gone back to using cellulose now for those reasons. Also, the company that we use now sprays a liquid in with the material that is supposed to act like a glue to keep it from settling. They can install it in an hour or less where when we did it ourselves it would take the better part of a day to do it. They also install it for less than we can buy the product for so why not let them do it. You do have to get up there and let them know you are watching though or they sometimes do it a little thin in spots. For a metal roof without anything under the metal, I would recommend spray on foam. Costs more but it really insulates well and takes care of the raindrop effect of the steel sweating.

k9mills · Nov 29, 2009

Rick,
Cellulose is much more corrosive to things like truss plates and connectors. Should you have a leak, heaven forbid, 8" of cellulose turns in to an inch or so of paper mache'. Fiberglas or mineral wool is much more forgiving. If your ceiling is anything like porous, put down a layer of tyvek or air tight membrane over the ceiling prior to installing the insulation. Tyvek or similar permeable memberane is far better than polyethylene as it allows transfer of moisture through the system without allowing air infiltration. If time and patience is available, it is well worth the effort to tape the tyvek seams and edges for an air tight installation. R40 insulation systems of any type are not effective unless you handle the air infiltration. Good luck with your project.
KM

Gun guru · Nov 29, 2009

I put that cellulose blown in crap in my home when I built it in 1999. I wish I would have bought the real r-30 fiberglass. the cellulose settles over time and you will lose more heat.
I put the cellulose in cause it was easier to install, now I regret it.

Anonymous-0 · Nov 29, 2009

Get prices from 3 reputable insulation contractors and foam it.

Shop Attic blow in insulation

Rick(MN)

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Joe in Neb

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fixerupper

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BCnT

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msb

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MSD

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k9mills

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Gun guru

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Anonymous-0

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