length of vapor barrier in basement

ottawa_daveOctober 24, 2006

Hey there,

I am finishing my basement...its about 7ft. below grade and I have just finished the framing. I am about to put the insulation in and then the vapor barrier (plastic sheeting) but I have been told two different ways in which to do this.!!!

One way is to take the vapor barrier right down to the concrete floor, and leave the top (by the ceiling) open.

The other way I was told was to leave about 1 - 2 inches between the end of the vapor barrier and the floor, and leave the top the same (open)....

Which way is correct? Thanks...


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If you look into the technical resource section of Building Science Corp., neither is correct; their call-out is to use no vapor barrier.

The thinking basically goes this way: Even the best-built basements potentially will leak moisture through the walls, either as liquid but also as water vapor. A vapor barrier will only serve to trap this moisture and create potential mold/mildew problems - potential health issues. The proper way to deal with this potential source of water is to limit the water entry through the walls and then let any that passes dry to the interior with vapor permeable materials of construction. That means no visqueen. One OK method is to insulate with white beadboard foam insulation and then drywall the interior. Fiberglass insulation isn't recommended because it holds moisture.

Here is a link that might be useful: Building Science Corp. - Basement Insulation Systems

    Bookmark   October 25, 2006 at 8:46AM
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I used construction adhesive to glue rigid foam insulation directly to the foundation walls, and no vapor barrier.

    Bookmark   October 25, 2006 at 3:32PM
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ditto to formulaross
just getting finished on basement - I did clean old fieldstone foundation walls w/stone cleaner then drylocked before framing -
Used Pressure treated for silplates, 2x4 framing and used moisture proof (used to be green board now purple), cut up aprox 3" in the event of water -

after much consideration for how to keep water out! - Do not trap water behind walls or barriers - it will only offer a false sense of security while a science experiment is brewing underneath everything

I did do external water abatement/diversion before commencing the remmodel as well - gutters, downspouts, slope of earth near foundation

good luck

    Bookmark   October 28, 2006 at 3:17PM
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The Code mandated sealed polyethylene over insulation is a recipe for wet mouldy walls. I feel guilty for all the basements I've insulated to Code.

If it's possible--slip in extruded polystyrene behind the framing using construction adhesive or tapcons and fender washers to secure to the wall. Then you can use batts, or beadboard or extruded or expanded polystyrene between the studs. No polyethylene.

If the wood framing is too close to the wall to slip in the polystyrene, I would detach the wall to get in the poly. Ontario's Building Code, including the 2006 version, has still got it all wrong on basement insulation.

    Bookmark   November 2, 2006 at 1:20AM
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