4 mil vapor Barrier versus 6 mil ??

Sep 20, 2008 3 Replies
W

Converting 300 sq ft garage into family room. Installing full floor above garage concrete slab. I want to put a polyethylene vapor barrier on the concrete.



Most places I read recommend 6 mil polyethylene. Home Depot selling for $50.



When cleaning out the garage I found a brand new box of 4 mil polyethylene that my Dad had given me.



Would it be a problem if I used the 4 mil that I have, instead of buying 6 mil?



I have a giant box. Can I double-up the 4 mil, creating a 8 mil barrier?



Thanks,



Chris


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H

might be ok if all seams sealed and overlapped. but plastic isnt forever. how old is it?

if your getting a permit run it by the local code enforcement building inspector

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T

Prob Ok if never exposed to sunlight! But 300sq ft. of 6 mil not very expensive? Assuming you have to insulate and vapour barrier the walls (unless they are already insulated and vapour barriered) use the 4 mil for that? Also what about the ceiling insulation and vapour barrier for a room that will now be heated, occupied by living breathing people and other activities that put out moisture; is that insulated and vapour barriered?

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K

Hi Chris,

Polyethylene is an extraordinary VB.

(I won't bore you with the details, but I use .1 mil for certain purposes, and it does the job.)

So, in your situation, the issue is fragility rather than the thickness needed to provide a barrier to the migration of moisture.

I would say "yes," you could use the 4 mil (and be careful to avoid tearing it.) Or, double it, and sleep a bit better.

All the best,

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