Should My Vapor Barrier Be Covered in Moisture?

LESLIE: Jo in North Carolina is on the line with a humidity question. What’s going on at your money pit?

JO: I recently – or maybe about a year ago – had a vapor barrier installed under there and a dehumidifier.

TOM: OK.

JO: And I was under there recently and I noticed that it’s really a lot of moisture under the vapor barrier. And I know the idea is to keep it from going up in the wood and the insulation and so forth but it just seemed like a lot of moisture. Is that to be expected?

TOM: That’s because you can now see it. It’s always been a lot of moisture. It’s now being trapped, so the vapor barrier is doing exactly what it’s intended to do: it’s creating a barrier against that moisture vapor getting up into your house. So that’s exactly what it should be doing.

Now, if you want to take steps to reduce the amount of humidity down there, I would tell you to look at the exterior drainage conditions around your foundation. Because, typically, where we see a lot of moisture is where the soil is very flat, it’s not sloping away from the walls. If downspouts are just dumping right at the corners of foundation, as they always almost always do – downspouts should be extended 4 to 6 feet away from your house – those are the kinds of minor improvements that can have a major impact on how much moisture gets under that house. But to see the moisture under the plastic, that’s where we want to keep it.

JO: OK. Now, my downspouts do drain away from the house but the other part of this was my dehumidifier that’s under there. I noticed that the hose that goes from the dehumidifier stays under the house, which I was surprised to see. I would have thought it would have gone outside, like my air-conditioner pipe and hose does.

TOM: Yeah, it’s just another source of moisture. So what I would do is I would run that hose out the foundation, near where one of the downspouts are, and run it either into the downspouts or along the downspouts so, again, that moisture is discharging away from the foundation.

JO: OK. Is that OK to put a long enough hose on it for it to go out into the yard and …?

TOM: It only needs a small hose, yep.

JO: Yeah, OK.

TOM: You can extend the hose.

JO: OK. Alright. That’s it. Thank you so much.

TOM: You’re welcome Jo. Good luck with that projects. Thanks so much for calling us at 888-MONEY-PIT.