How to Manage Crawlspace Moisture
LESLIE: Melvin in Minnesota is calling in with a mold issue. What’s going on at your money pit?
MELVIN: I have a cabin at the lake and it’s built on a crawlspace; there’s this crawlspace underneath there.
MELVIN: And I have mold under there. What can I do to remedy that?
TOM: Hmm. Do you have a lot of mold or a little bit of mold?
MELVIN: Well, quite a bit; more than there should be.
TOM: Wow. Well, first of all, we need to address the environmental causes of mold growth, which are humidity and moisture. And on a lake space, especially, it’s obviously going to be very damp. But there are a couple of things that you can do to dry out the crawlspace.
Number one, you want to make sure that you have gutters on this house and that you’re managing roof water. We don’t want to dump a lot of water around the foundation, Melvin. And number two …
MELVIN: Now, we’ve got those.
TOM: Oh, you do have those. OK.
MELVIN: (overlapping voices) The water level is fairly high, too, see.
TOM: You want to make sure the downspouts are extended out away from the foundation by at least four to six feet.
And then the second thing is take a look at the grading and make sure that – at least around the foundation perimeter ; the first four feet – the soil slopes away. You want to make sure that you have proper crawlspace vents; at least one on every side of the house, maybe two. And you also want to add a vapor barrier across the soil. So that would be plastic across the soil with no gaps, if possible.
LESLIE: Mm-hmm. You want to overlap it so you’re not getting any gaps. And if you can overlap it a good foot just to really make sure you get a good seal, that would be very helpful.
TOM: Now, in terms of the mold that’s already there, you probably should treat that to kill it. And you can do that by spraying it with a bleach and water solution or you could have a professional spray a product that will do it. I know that pest control operators frequently will treat mold as well.
But one way or the other, you need to treat that mold to kill it. If it dried out to, say, below 25 percent moisture, it will die on its own but since it’s really taking hold, I would definitely spray it.
And lastly, the last thing you do is make sure you do an inspection of the structure because when it gets moldy down there, the floor joists start to rot from the inside out. So what you do is you crawl around in there and you poke the sides of the floor joist or the sills with a long, metal probe – like a long screwdriver will work – and make sure if you have any rotted areas that you repair or you replace them. You could sister any bad floor joists by putting new ones next to it.
So, that’s what you need to do but I would do it sooner rather than later, because it’s only going to get worse.
MELVIN: OK. You don’t recommend to dig out the dirt and to replace it with gravel or anything like that, huh?
TOM: No, no. It’s a moisture management issue, Melvin. You’re not going to make the dirt go away. The moisture is going to be there whether it’s dirt or whether it’s gravel and if you don’t manage it, it’s going to continue to get worse.
MELVIN: Oh, yeah. Mm-hmm. OK. Thank you very much.
TOM: You’re welcome, Melvin. Thanks so much for calling us at 888-MONEY-PIT.