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LITIMJO

09:50AM | 02/28/03
Member Since: 01/15/02
25 lifetime posts
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Vapor Barrier Installed Under Subfloor

Tags: HVAC
My den area is over a crawlspace. There was never any insulation installed under the floor. The crawl space has a scratch coat of cement on the floor. But what was done was that a vapor barrier was stapled to the bottom of the subfloor, apparently prior to putting down the subfloor since it runs right on top of the floor joists also. I seem to remember hearing this is not a good situation. Should I cut this away before I install the insulation or can a just leave it in place and install the insulation over it? Even if a cut it away, I'm not sure if I could get it out from under the joist.
I tried posting this in Basements but got know reply. Thanks

homebild

03:56PM | 02/28/03
Member Since: 01/28/03
693 lifetime posts
Of what is the 'vapor barrier' stapled to the bottom of the subfloor made?

LITIMJO

01:55AM | 03/01/03
Member Since: 01/15/02
25 lifetime posts
Sorry, it is the 6 mil thick polyethylene that I usually see recomended for the ground on a dirt crawl space.

LITIMJO

08:41AM | 03/07/03
Member Since: 01/15/02
25 lifetime posts
Back to the top hoping for a reply.

Housebroken

01:41AM | 03/23/03
Member Since: 12/23/02
18 lifetime posts
It depends on your climate. If I'm understanding you, the vapor barrier is just beneath the subfloor, but on top of the joists. In a cold climate, it's fine where it is. You want the vapor barrier on the warm in winter side of the insulation. You would simply install your insulation between the joists, underneath the poly.
You can also add a vapor barrier to the crawlspace floor, but there may already be one under the concrete.

Lawrence

10:53AM | 04/12/03
Member Since: 11/14/00
333 lifetime posts
It depends on whether your crawlspace stays somewhat warm in winter or gets as cold as the outdoor air.

If your house is elevated and the crawlspace is under that elevation so as to be exposed to the outdoor air, then you are fine: install the insulation between the joists, with the vapor-barrier between the insulation and the interior or your house.

However, if your crawl space is underground or if it is insulated from the outdoor air, itself, then that vapor barrier could end up trapping moisture inside the crawl space, which could condense inside the insulation and rot it out. If that is the case, then either ripping out the current barrier or leaving it in could be the proper remedy. We can't tell from here.

Take a look at some of the other recent posts for the purpose of a vapor barrier to judge for yourself. There are also relevent posts under "Basements" on this Bulletin Board.

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