Air, odor and radon from below

Warm air rises and leaves a building at the top, and replacement air has to come from somewhere. In a great many houses a meaningful share of it comes from the bottom — from the crawl space or the basement, through gaps around plumbing, ducts and framing. That is the reason a damp crawl space is not only a crawl space problem: the musty smell upstairs is the same air, relocated.

The practical consequence is that humidity control below is worth more than it looks. A dehumidifier in a sealed crawl space or a basement does real work, but only within limits: it removes moisture from air, and it cannot keep up with a source that is replenishing itself — standing water, a leak, or bare soil with no vapor barrier over it. Running a dehumidifier against an unsolved water source is the most common way people spend money on this problem without changing it.

Radon belongs here too, because it arrives by the same route. It is a naturally occurring soil gas that enters through the ground contact points of a building, so it concentrates in the lowest levels, and the only way to know your level is to test. Two overlaps with the rest of this site are worth flagging. A sump pit is an opening to the soil, so it is both a common radon entry point and a common place to tie a mitigation system into. And encapsulating a crawl space changes how gas moves under a house — a sealed vapor barrier can be part of a mitigation strategy, but sealing alone is not mitigation, and assuming it is has left plenty of people with a false sense of security.

Consistent with the rest of the site, we stay on the building side of the line. We cover testing, the mechanics of how mitigation systems work, and how they interact with drainage and encapsulation. We do not write about health effects or exposure risk — for that, the EPA and your state radon program are the sources, and they are the ones we point to.

Air, odor and radon from below

What's down there doesn't stay down there

Sources