Musty Odor in Home on Concrete Slab

Find out why a musty odor in a home on a concrete slab isn’t unusual if the house has been unoccupied for a long time. The smell should clear up once you move in and start running the HVAC system.…

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LESLIE: Mary in Virginia, welcome to The Money Pit. What can we do for you today?

MARY: I’m looking to purchase a home that has a slab foundation. And when I went in, I kind of smelled a musty, mildew-y odor. And I’m just wondering, how would you know that water is coming up from the ground and saturating that slab? And how do you protect a home that has just – that’s built just on a slab. They’re nothing under for water to drain under or anything.

TOM: Was this a home that was vacant or did it have a family living in it?

MARY: It has been vacant for a while.

TOM: And that makes sense. Because when you don’t run the HVAC system as frequently as you would if it was occupied, sometimes you’re going to get high humidity inside the homes. But because it’s a slab doesn’t make it any more or less susceptible to water infiltration. But of course, because it’s above grade, you don’t get floods. What you do get is the power of the concrete basically drawing water up from the ground – it’s called “capillarity” – and then letting it evaporate into the air.

The correction for that is the same thing you would do even if you did have a basement, which is to improve your drainage on the outside: extend the downspouts, the gutters; improve the soil slope so that water is sort of shunted away from the foundation perimeter. But I think that once you move into the house and use the HVAC system, you’re going to find that that moisture is not nearly as detectable as it is right now. And if it does become more detectable, you could always add a dehumidifier.

MARY: OK. So it’s the – that smell I’m getting is not coming from the carpeting that’s on top of the – laying on top of the slab?

TOM: Ooh. Carpet on top of slab? That’s a bad thing.

MARY: Well, I mean I don’t know what’s under the carpet and I’m assuming that there’s some kind of subfloor there. But yeah, it’s wall-to-wall carpeting and I know underneath it is basically a …

TOM: Yeah. We don’t like carpet on concrete, for a whole bunch of reasons. So I would be recommending that you find another type of flooring for that. Because when you put carpet, which is largely an organic material, against those damp, moist, concrete slabs, bad things happen. You get mold and mildew growth, you get allergens that form, you’re going to get dust mites, things like that. So, we really don’t like carpet on concrete slabs. If you can choose a different type of flooring, if you’re going to do some remodeling, that would really help out a lot.

MARY: OK. Thank you so much.

TOM: You’re very welcome, Mary. Thanks so much for calling us at 888-MONEY-PIT.