How to Fix Damp Crawlspace
LESLIE: Lynn in North Carolina needs some help with a crawlspace project. What can we do for you?
LYNN: I was just wondering if you could advise me as to whether or not I could do this myself or whether I had to get a company to help me. And what it is is my basement is partially finished and partially a crawlspace. And in the crawlspace, there’s just bare dirt. And it typically doesn’t have a lot of moisture unless it’s really, really, really rainy. And I just felt – feel like I need to cover it with some sort of plastic or some sort of barrier to help keep that humidity down.
TOM: You’re exactly right, Lynn, and it definitely is a project that you can do yourself as long as you can, you know, physically get into that crawlspace. But let’s start outside because the moisture does form from the outside in. You want to make sure that your gutter system is clean, that the downspouts are extended not 2 feet, which is the way they normally are, but 4 to 6 feet from the house. You really want to go through a good effort to get those downspouts at least a few feet out from the house.
And then, thirdly, make sure the soil around the house slopes away. Those three things – gutters clean, downspouts extended and soil sloping away – do most of the work in terms of keeping those below-grade spaces dry.
Now, in terms of the crawlspace itself, what you want to do is – I typically would say rake the dirt surface so it’s nice and flat and there’s nothing in there that can kind of break through the plastic. And then what you want to do is just take some very heavy plastic, some clear plastic like Visqueen, and then start laying it down across the crawlspace-dirt surface.
And you want to put it in in as few pieces as possible. And if you have to overlap it, overlap it 3 feet, alright? Because that’ll do a good job of keeping that moisture and humidity from evaporating out of that soil and then getting into the air and the basement and working its way up into your house. So it’s really as simple as that.
LYNN: OK. And any particular type of plastic or are we talking just go to Lowes or Home Depot and get …
TOM: Well, what you want to do is find a plastic that’s about 6-mil thick. It’s usually just called “reinforced polyethylene construction film” or something of that nature. It comes in rolls that are usually about 12-feet wide and about 100-feet long. No, the roll’s not 12 feet; it’s usually about 4 feet and it’s just overlapped. But you buy these big rolls and you roll it out and cut it and then unfold it. And again, get it across that whole floor surface. You can let it lay up against the wall a little bit. And then if you have to overlap it, go ahead and make sure you overlap it by about 3 feet.
LYNN: And do you pin it with something of some sort? Do you pin it with some sort of nail?
TOM: No, it just stays there by its lonesome. It’s not going to go anywhere as long as you’re not – as long as you guys don’t like to crawl up in that crawlspace a lot.
TOM: No, it’s a really easy project to do yourself.