Radon in older homes: dirt floors, crawl spaces and stone walls

Test first

The only way to know is to test.⁠³ Put the kit in the lowest level of the home that is or could be used regularly, finished or not, but not in a crawl space.⁠⁴ The Health Department Lab’s long-term kit is $25.⁠⁵

Fixes by foundation

The EPA groups radon fixes by foundation design. When part of a home has a basement and the rest a slab or crawl space, a combination may be needed.⁠²

Dirt floor or crawl space

The contractor covers the earth floor with a high-density plastic sheet, and a vent pipe and fan draw radon from under it to the outdoors. The EPA calls this submembrane suction and says, when properly applied, it is the most effective way to reduce radon in crawl space homes.⁠² Drawing air straight out of the crawl space with a fan generally doesn’t work as well and can raise energy costs.⁠²

Concrete basement floor

Suction pipes go through the slab into the crushed rock or soil beneath, and a fan vents the radon outdoors. The EPA calls this subslab suction, the most common and usually the most reliable method.⁠²

A sump pit

The sump can often be capped so it keeps draining water and also serves as the radon suction point.⁠²

Hollow concrete block walls

Block-wall suction draws radon out of the hollow blocks, often together with subslab suction.⁠²

Fieldstone walls

The EPA’s 1993 technical guidance for contractors says subslab suction can work in houses with fieldstone walls, but there is a greater chance another technique will be needed to supplement or replace it.⁠⁶

Whether your home needs diagnostic tests first depends on its foundation, what’s under it, and the contractor’s experience with similar homes.⁠² The Health Department estimates $1,500 to $2,500 to install the common vent-pipe-and-fan system.⁠⁷

If your result is 4.0 pCi/L or higher

The Health Department says to contact a certified radon mitigation contractor.⁠⁷ Search either national directory it points to: NRPP or NRSB.⁠⁸

Questions? The Health Department’s Radon Program: 802-863-7220.⁠⁸

Find a certified contractor What your number means

What doesn’t work on its own

• Sealing cracks. Sealing helps other fixes work, but the EPA doesn’t recommend sealing alone: it hasn’t been shown to lower radon significantly or consistently, and a house settling opens new gaps.⁠²
• Opening windows. Radon most often returns to its earlier level within about 12 hours of closing them, so the EPA calls it temporary.⁠²

Can I fix it myself?

The EPA recommends a qualified radon mitigation contractor, because lowering radon takes specific technical knowledge and skills; without them, you could raise your radon level or create other hazards.⁠² If you decide to do the work yourself, the EPA says to ask your state radon office about training. In Vermont, that’s the Health Department’s Radon Program: 802-863-7220.⁠^2,8

Common questions

Can radon be fixed in a house with a dirt-floor cellar or crawl space?

Yes. The EPA says covering the earth floor with a high-density plastic sheet and drawing radon from under it with a vent pipe and fan, called submembrane suction, is the most effective way to reduce radon in crawl space homes when properly applied.⁠²

Will sealing the cracks in my foundation fix radon?

Not by itself. The EPA doesn’t recommend sealing alone, because it hasn’t been shown to lower radon significantly or consistently; sealing is a basic part of most other fixes.⁠²

Can I install a radon system myself?

The EPA recommends a qualified radon mitigation contractor. If you do the work yourself, it says to get information on training from your state radon office; in Vermont, that’s the Health Department’s Radon Program.⁠²