Dirt Is Not a Floor: A Crawlspace Love Story

Your house and the dirt under it have a long history. The dirt keeps sending up moisture, the house keeps soaking it in, and nobody wants to talk about it. It’s not a healthy relationship, so I put on a headlamp, crawl in there, and play counselor.

The fix is a vapor barrier, which is just a big sheet of heavy plastic laid over the dirt. It puts some much-needed distance between the two of them.

Here’s why it matters. Dirt gives off moisture all the time, even when it looks bone dry. That moisture gets into the framing and insulation and invites mold, rot, and wood-eating bugs. Upstairs, you’ll notice a musty smell and a house that feels a little damp.

“But it’s dry in Colorado.” Sort of. Snowmelt, sprinklers aimed at the foundation, and downspouts that dump right by the wall all send water under the house.

What I usually find is no barrier at all, or plastic that’s torn, bunched up in a corner, or only covering half the floor. Sometimes it’s decades old and about as flexible as a potato chip. A few have clearly been someone’s storage tarp.

A good one covers the whole floor, with seams overlapped about a foot and taped, and it runs up the walls and piers a bit. Go with at least 6 mil, and thicker is better. If there’s standing water, fix the drainage first, because plastic can’t save soggy dirt. A good barrier can also help keep radon from creeping up through the soil, which is one more reason to ask me about radon testing.

You can DIY it in a small, dry crawlspace if you don’t mind tight spaces. Wear gloves and a respirator, since there can be droppings and plenty of dust. If it’s big, damp, or full of critters, call a crawlspace pro.

If you’re buying and I find a missing or shredded barrier, don’t panic. It’s common and fixable. If you’re selling, a fresh sheet of plastic is a cheap way to get ahead of it.

Dirt belongs in the yard. Your crawlspace deserves better.