My buddy has wood frame, 2 story, 2 car garage. The upstairs of the garage is air conditioned space (his office).
He wants to insulate the floor (or ceiling depending on where your standing) between the bottom story and the top.
This is in Florida. Extremely hot and humid most days.
My suggestion was fiberglass bats (thats what he wants to use) with 6 mil poly stapled to the floor joists.
question here is if he uses kraft paper backed fiberglass, would the paper go against the floor or facing the garage floor?
Would it be best to get unfaced, use the wire hangers and the the poly?
Does it matter whether the paper is there or not?
your thoughts.
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WWPD
Replies
I thought in FLA the vapor barrier would go toward the outside, so in your case toward the unconditioned garage space. Here, people have all but stopped using plastic vapor barriers due to mold concerns - ie trapping moisture - so if fiberglass insulation is to be used, kraft paper is the preferred material since it is really not a great vapor barrier.
Additionally, you need a really good air barrier on the garage ceiling to help reduce the possibility of carbon monoxide from the garage from getting up to the finished room above, so finished drywall on the garage ceiling with well sealed edges would be a requirement. and local codes might require 5/8" for fire safety reasons.
Here's my thoughts,
Un-faced f/g batts or rolls, friction fit into bays(no need for hangers), install Tyvek over joists with printed face down, cover w/ 5/8" firecode sheetrock, tape and mud, being sure to seal around perimeter and all penetrations.
Do not use poly, it will trap moisture.
Geoff
Foam it.
The weather was hot, a-nearly 90 degrees.
The man standin' next to me, his head was exploding,
Well, I was prayin' the pieces wouldn't fall on me.
Like already mentioned, I'd look into spray foam insulation. Best R-value, unaffected by mositure so there should be no need for vapor barrier, and will make an air-tight seal.
I will ditto the spray foam and the 5/8" drywall
The Garage should be "Isolated" from Living space
JB
I have preached the foam to him..to no avail.
The garage is just going to be used for storage--no cars.
He does want to finish it though with drywall.
Strange how the trends change.
I talked with a Johns-Mansviller rep about a year ago about fiberglass bats in the home walls for a house down here and he said ideal scenario would be the poly on the outside.
Now no poly. Go figure.
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WWPD
Since you asked about "best" he needs spray foam.Butr I wouldn't for a job like this.He really does need the SR barrier for fire safety and to control infiltratyion. He cuts the effectiveness of batts in half if he doesn't control airflow.So for "cheap" instead of good opr best, I'd say he is boxing himself in to limited choices and the best of those is to install unfaced batts and then run plastic across the faces of the joists.
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I would not insulate it, fla is pretty much a constant temperture, it doesnt freeze, it doesnt get cold. most temp lost is out the roof. in fact it reccomended that insulateing floor is a waste of money. Insulate the walls with r13 throw r40 in the attic and forget about the floor. no vapor barrier anywhere.
Comeon now! I lived three years there and saw temps run from 18° up to 123°F That is not very constant! Maybe less range than CO where it ran -60° up to 115°F but still...The differential he would be insulating against though is that between the AC office at 70° and the exterior or the cieling of the garage at 100+ so that is a diff of about 35°. That can help pay his AC bill if he does it cheap enough.
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I'm not sure how things are done in Florida but around here the vapour barrier is always on the side facing the room and the insulation closer to the cold (in your case the hot).
An easier solution for you might be simply stapling your 6mil poly to the underside of the floor joists. Then go over it with 1 1/2" rigid foam insulation. Done! Then finish off with 5/8" Fire Resistant drywall (depending on the building code for your area of course) .
Dave
well since he does not want foam insulation how about cellulose blow-in??? I have not priced it compared to fiberglass batts. I think it gives a slight better R-value.