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iLearn

join:2013-01-16
canada

Spray foam insulation over Cellulose Insulation

Can we use spray foam insulation over cellulose insulation in the attic? Or do we have to remove the cellulose or any other type of insulation before using the spray foam.

Any web links?

Thanks


Msradell
P.E.
Premium
join:2008-12-25
Louisville, KY
Normally when spray foam is used in an attic it is sprayed to the underside of the rafters (hot deck installation) and the attic area becomes conditioned space. This obviously could be done with the cellulose insulation still in place because you would create 2 different temperature zones.

I don't believe what you are proposing would work because you would not have a solid surface to spray the foam against.

iLearn

join:2013-01-16
canada
Yes, it makes sense.

How about if we put loose fill fiber glass insulation on top of cellulose or any other type? Is that OK.


LazMan
Premium
join:2003-03-26
canada
reply to iLearn
What's wrong with more cellulose ontop on the existing? It's still very common as attic insulation...

If you are going to do sprayfoam, standard procedure would be to remove the existing cellulose/fiberglass/etc - and apply the foam directly to the topside of the ceiling drywall/plaster.

iLearn

join:2013-01-16
canada
Lets just say someone likes pink

kherr
Premium
join:2000-09-04
Collinsville, IL
Reviews:
·Charter
reply to iLearn
My only experience with cellulose was breaking open some bags in the attic to bury some duct work. Opened the bag and then fluffed it up with a rake. When I went back up there some 18~20 years later it had settled by at least 50%. A few months ago I added some more insulation to replace what the tree rats made off with and used fiberglass. There's some video on youtube that not only shows how cellulose settles, but showed how it will disintegrate if exposed to heat from a simple light bulb. It sold me on fiberglass real quick even though it has a little bit fewer R's when compared to cellulose.


alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1
said by kherr:

It sold me on fiberglass real quick even though it has a little bit fewer R's when compared to cellulose.

In attics, the R per inch becomes irrelevant. It's all about the R per $. So ya, who cares if fiberglass is less R per inch.

To OP: Spray foam is the most expensive $/R ratio in a location that doesn't require efficient high R/Inch. So why do you want to spray foam? To answer your second question: Yes you can put fiberglass over cellulose.

Tig

join:2006-06-29
Carrying Place, ON

2 edits
reply to iLearn
Spray foam on top of cellulose would put a vapor barrier on the wrong side of the insulation. Bad idea.
Loose fill on cellulose is fine.
Check out the "attic cat" product and loaner blower at your local big box lumber depot.

robbin
Premium,MVM
join:2000-09-21
Leander, TX
kudos:1
reply to alkizmo
said by alkizmo:

In attics, the R per inch becomes irrelevant. It's all about the R per $. So ya, who cares if fiberglass is less R per inch.

Sounds like you have never crawled in a 3 or 4/12 pitch attic.


jkj860
The Final Frontier

join:2002-01-10
Valparaiso, IN
reply to iLearn
If you use fiberglass rolls added to existing, just make sure you use unfaced. (no vapor barrier)


alkizmo

join:2007-06-25
Pierrefonds, QC
kudos:1
reply to robbin
said by robbin:

Sounds like you have never crawled in a 3 or 4/12 pitch attic.

5/12 but I undeerstand.
You can still blow the insulation instead of putting batts.