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rtoni 08-14-2007 03:59 PM

crawlspace plastic (6 mil)
Hi - seen a few posts here on crawlspace moisture control - common suggestion is to run 6 mil poly over the floor and up the wall.

the guys helping me with the slab plan to snap a chalkline around the wall to level the floor. They apparently work the wall edge by eye. This implies I can't have the poly run continuous up the wall (it would be in their way, pretty much). So I end up with poly under the entire floor (good), but nothing on the walls (which are insulated outside, but will not be insulated inside).

can I go back later and somehow cover / seal the joint where the floor meets the wall and the wall itself - maybe a sheet of poly that starts on the floor about a foot or so out from the wall (caulked) and then runs into and upwards against the wall to the sill plate (sealed there too)....? does this make sense - would this work ok...?


Ron6519 08-14-2007 04:20 PM

This is confusing in that I don't know what state the crawl space is in. Are you putting concrete over soil and want to know where the vapor barrier goes? Are you snapping chaulk lines for a reason? Where do you live? You might benefit from foam insulation under the concrete.
Plastic runs up the walls when you only have a dirt crawlspace.

rtoni 08-14-2007 04:31 PM

sorry for the confusion
the crawlspace footings and wall (block) are in place. Floor (slab) is pending.

I've read several articles, etc. that indicate a plastic barrier (one that continues up the wall) is what I'd need for a dirt floor - as you mentioned. My intention is to run poly and pour slab over that

I've heard that in this case, the poly still should run continuous (come up from under the edge of the slab and run up the wall). Are you saying this is bad information?



Ron6519 08-14-2007 05:42 PM

In your case, the wall vapor barrier would be addressed on the exterior with a rubber membrane from the footing up the wall to above ground level. In front of that would be a layer of foam insulation that protects the membrane from damage when backfilling and thermal protection.
I never heard of a continuous plastic sheeting in your circumstance.
Where do you live? You might benefit from foam insulation under the concrete.

rtoni 08-15-2007 10:18 AM

I'm in ontario canada
thanks for the replies and the help

footings here will only be backfilled about 30" - i planned on using foam on the outside as you mentioned mostly because I want to shorten the frost depth (shallow frost protected foundation design - foam boards on the walls and then extending horizontal - across the footing as well). Would foam under the slab help in this situation?

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