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Old 12-08-2010, 12:47 PM   #16
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interior french drain with integrated vapor barrier is a good idea?


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Originally Posted by itsreallyconc View Post
good guys leave it at least 6" above the floor/wall joint ( cove ),,,
in my case they left @ 16" - guess that makes them really good guys

just recalling - fwiw - when they quoted my job the boss went out to the truck and grabbed a small electric hammer and started busting out a part of what looked like the old attempt to fix the problem (someone created a kind of a trough around the inside perimeter along the walls). He walked thru this stuff like butter. I'm not sure if he based the final quote on that ("hey this is pretty easy") but when the 2 guys on his crew came in for the actual work the next day they got a bit of a surprise. Concrete must have been cheap in those days 'cause they hit spots 8" deep in parts of the floor and it was tough stuff. The compressor and jackhammers showed up in the driveway the next day - and they still had a workout. When I saw that stuff coming up I was pretty glad I didn't try to take on the job myself. I think they expected a thin layer on the floor. Sure wish they built the rest of the house that way back then (the carpenter could have taken some pointers - or maybe borrowed a level - from the concrete guy)...

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Old 12-08-2010, 05:27 PM   #17
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interior french drain with integrated vapor barrier is a good idea?


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Don't count on it. What happens if you get enough condensation on the barrier to have moisture there, but not enough for it to drain down? (think fogged up mirror).

Vapor barriers in a basement are a bad idea. Concrete is porous-- it needs to be able to breathe to dissipate vapor that it gives off. Trapping the moisture will lead to condensation, and condensation to mold.

Worse yet would be a barrier right against the concrete with no airspace. Air stores moisture, giving a moderating effect on wet/dry extremes. With no air gap, you'll either be quickly wet enough to condense (and mold), and the dry air won't be able to access the moisture and achieve equilibrium.

So what to do in a basement? Slow down the vapor emission from the poured walls with a retarder. Insulate to raise the surface temp above the regular concrete surface temp (and buy condensation margin). Unfaced rigid foam conveniently does both in one fell swoop, as long as it's <2" thick (most rigid foam is a vapor "barrier" if thicker than 2"-- unfaced)
Yes, you are right. I definitely will use 2" rigid foam to insulate the basement walls and floors which will reduce or avoid condensation in the summer. I am thinking if we have a barrier between the rigid foam and the walls/floors, it will be an extra protection. Because of the 2" rigid foam insulation, there will be no or very little condensation on the barrier.

During the summer time, the barrier can reduce moisture migrate from exterior to internal via walls/floors. If there is little condenstaion in the summer, it will dry out in the winter for the exterior side of the barrier. For the internal side of the barrier, there may be problem if it get condensation but barrier (plastic sheeting) and rigid foam will not support mold.

So, no barrier will be safer because summer moisture/condensation will be dry out to exterior via walls/floors during the winter? Right?

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