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Eddie Bear 07-03-2011 01:16 AM

crawl space vapor barrier help
I just bought my first house. (FYI)
Its a single level ranch with a crawl space.
The crawl space has some type of clay.
No signs of mold. The crawl space has two outside wall vents.
The A/C drains in to the clay so I plan to install a condensation pump.

There is a plastic vapor barrier down there but it has many holes and covers about 60-70% of the soil/clay. (the crawl space is about 26'x41')

I want to install a new vapor barrier.
Here is the question, Can I install the NEW vapor barrier OVER the OLD one?

My thinking is that moisture will get trapped in between the layers THEN cause mold.

The photo shows the condition.

Ron6519 07-03-2011 06:25 AM

I'd clean out all the garbage(old barrier included) and put down a new barrier that covers the whole floor.

Eddie Bear 07-03-2011 10:15 AM

Thanks Ron.
That's what I though. There is garbage down there (old shoes, tile, pipes).

Is it bad to have the barrier over the cast iron drain pipe?
That's how it is now. I a little worried about tampering with pipes that old. (I have that kind of luck)

Eddie Bear 07-03-2011 10:26 AM

OK, then about the mil of the plastic. Between 4, 6 and 10 mil, 10 would be best right?
I see 20'x100' 10 mil online for $119 (Home Depot its $199).
Is the higher the mil, the thicker the plastic?

AGWhitehouse 07-03-2011 02:28 PM

You can cover the pipe and yes the higher the mil, the thicker it is.

Ron6519 07-03-2011 04:02 PM

Six mil is the standard in vapor barrier thickness.

jklingel 07-04-2011 02:30 AM

I'd only spend the money on 10 mil if you were planning on using the crawl space frequently. Be sure to run it up the walls, secure it, and caulk it w/ a compatible caulk, something like Tremco acoustical caulk.

Gary in WA 07-04-2011 08:36 PM

As we don't know your location, only run the plastic up the concrete walls 6", to inspect for termites.
You may need to take special precautions if in a radon zone:


John_W 07-04-2011 11:06 PM

Clean it out for sure. You are breathing air that comes from your crawl space.

Gary has a good point about radon. If you have to mitigate for that, the quality of the plastic and the way it is installed will be more important.

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