Vapor barrier is "stapled" to what?

Inspecting an early 70’ multifamily buildings crawlspace I see clear plastic (obviously an issue) that was somehow “stapled/secured” to the earth & the adjoining sheets of plastic. Gentle tugging and prodding couldn’t lift the plastic. The floor of the crawlspace also felt unusually flat and I could feel a slight texture under the plastic with visible condensation on the underside of the plastic.

So my questions:

  1. Has anyone seen some type of underlayment laid in a crawlspace below the plastic? I suspect (but couldn’t prove) that there was a fibrous material that the plastic had been stapled / secured to.

  2. Condensation on the underside of the vapor barrier: Issue or the plastic doing its job?

Thanks for any insights anyone can provide.

I have not. Typically I see are black or yellow and don’t feel anything underneath.

Theoretically it is doing it’s job but if the mil thickness isn’t the proper mils then you are going to get more vapor through the material.

It looks like it could be 4 or 6 mil in thickness, probably 6, 10 miles is better and what is typically recommended in the industry. I would write it up as being an incorrect material, but have the seller confirm through receipts the mil thickness.

The seams must be overlapped and taped with the appropriate tape though. I can’t recall the minimum overlap at the moment but you should look it up.

Welcome to our forum, Tom!..enjoy participating. :smiley:

It is doing its job but is best when the seams/walls/protrusions are taped to complete the seal

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6 inch min. overlap and taped. Equally important is the amount of ventilation openings in the crawlspace.

I hate to say it, but I would have found a way to determine what it was stapled to in an inconspicuous place.(peek, pull, peel, pry, peer). Even if my curiosity might get me in trouble, lol.

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Was there a Radon System operating?