Radon mitigation (sub-slab depressurization)

Works, the settled fix

Stasis Home ResearchEvery claim on this page is graded against peer-reviewed health research and linked to its primary source.Updated 2026-06

Sub-slab depressurization is the established fix, with decades of settled engineering behind it. A pipe through the foundation and a small always-on fan pull radon out of the soil before it reaches your living space, cutting indoor levels by 80 to 99 percent. A certified contractor installs it, and the same test that found the problem verifies the fix. Sealing cracks alone fails, and EPA says so directly.

How it works

Radon gets in because your house gently sucks on the soil beneath it. Warm indoor air rises and leaks out high in the building, which leaves the lowest level at slightly negative pressure, and soil gas flows up through slab cracks, plumbing penetrations, and sump pits to fill the vacuum. Sub-slab depressurization reverses that contest. A contractor cuts a small hole in the slab, runs a PVC pipe from the soil beneath it up past the roofline, and mounts an inline fan that runs continuously on 60 to 90 watts. The fan holds the space under the slab at lower pressure than the house, so soil gas follows the pipe to the open air above the roof instead of seeping into the rooms below. Sealing the visible cracks and capping the sump is part of every proper install, because a tight slab helps the fan hold its pressure field. The fan is what does the work.

What it handles, honestly

What this approach does and does not take care of.
Concern	Handled?	The honest note
Radon in slab-on-grade homes	Yes	Sub-slab suction is EPA's recommended standard for this foundation type. A correctly installed system cuts indoor radon by 80-99% (EPA Consumer's Guide).
Radon in homes with basements	Yes	Same fan, different suction point: drain-tile, sump-hole, or block-wall suction depending on how the foundation sits on the soil. A certified mitigator picks the variant after inspecting the house.
Radon in crawlspace homes	Yes	The submembrane variant: a ground cover sealed over the exposed soil, with the fan drawing from beneath it so soil gas never reaches the crawlspace air.
Radon blamed on granite countertops	Yes	EPA calls countertops a minor source; the soil under the house is almost always the real driver. If the air tests elevated, the fan system is the fix whether or not you have granite. Countertop replacement is almost never warranted.
Radon dissolved in well water	No	A soil-gas system does not touch water. Private wells near uranium-bearing rock can release dissolved radon indoors during showers and dishwashing; the fix EPA names is whole-house aeration, roughly $3,000-5,000 installed. Activated carbon is not recommended here because the spent media concentrates radioactivity.
Stuffy air and CO2 buildup	No	The fan moves soil gas, not indoor air, so it adds no ventilation. When radon shows up alongside high CO2, VOCs, and moisture, an HRV/ERV earns consideration as the cross-cutting fix: a 39% median radon reduction (Gaskin 2025) plus the fresh air the house is missing.

Getting it right

This is a contractor job, and the credential to ask for is an NRPP listing (the National Radon Proficiency Program, the certification radon mitigators carry). EPA's national install range is $800 to $2,500; local labor rates set where you land. The fan draws 60 to 90 watts around the clock, roughly $150 to $250 a year where electricity runs 30 to 40 cents per kilowatt-hour and less where power is cheaper, and the fan itself is a $300 to $600 replacement sometime in years five to ten. Verification is built into the protocol: retest with a continuous monitor starting 24 hours after the fan turns on, under closed-house conditions for at least 48 hours, looking for a reading below 4 pCi/L and ideally below 2. The system variant follows your foundation, so the right first step is a measurement of the home's air at the lowest occupied level, then a mitigator's inspection, never a product order.

Common questions

Can I just seal the cracks in my foundation?

No. EPA's guidance is direct: sealing alone has not been shown to lower radon levels significantly or consistently. On its own it manages a 10 to 30 percent reduction. Sealing belongs inside a fan-driven install, where it helps the system hold suction under the slab; it is supplemental, never the fix.

How much does radon mitigation cost?

EPA's national install range is $800 to $2,500, set mostly by local labor and how your foundation is built. After that, the always-on fan costs roughly $150 to $250 a year at high electricity rates and less at average ones, plus a $300 to $600 fan replacement somewhere in years five to ten.

How do I know the system is actually working?

Retest. The protocol is a follow-up measurement starting 24 hours after the fan turns on, run at least 48 hours under closed-house conditions, with a target below 4 pCi/L and ideally below 2. A recheck at six months and then annually confirms the fix is holding.

Will a ventilation system fix radon instead?

Partly. Balanced mechanical ventilation (an HRV or ERV) cut radon by a median of 39 percent in peer-reviewed Canadian field work, with a 29 to 50 percent range. That is meaningful but well short of the 80 to 99 percent a sub-slab system delivers. For radon alone, the fan wins on results per dollar; the ventilation route makes sense when stale air, VOCs, and moisture need fixing too.

My house is new. Do I still need to test?

Yes. Tight modern envelopes hold heat well and hold radon too: in a large Canadian survey, homes built after the energy code tightened averaged about 30 percent higher indoor radon than older stock. Most US states do not require radon-resistant construction in new builds, so a recent build date tells you nothing about the reading.