How radon mitigation works

Radon enters a house because the air pressure inside is usually slightly lower than the pressure in the soil underneath. The house literally inhales soil gas through cracks, joints, sump pits and utility penetrations. Mitigation doesn’t try to seal every crack — that approach fails on its own — it reverses the pressure difference so the soil gas never gets in.

The standard fix: sub-slab depressurization

For homes with a basement or slab, nearly every professionally installed system is some form of active sub-slab depressurization (ASD). It has four working parts:

• Suction point: the pro cores a hole through the slab and digs a small pit beneath it, so the pipe can draw air from the soil across the whole footprint.
• PVC piping: a 3–4″ pipe runs from the pit up through the house (or up an exterior wall) to above the roofline.
• Inline fan: a continuously running fan — mounted in the attic or outside, never in living space — keeps the soil under constant gentle vacuum.
• Manometer: a simple U-shaped gauge on the pipe. Uneven fluid means the fan is pulling; level fluid means the system is down. It’s your at-a-glance health check.

The discharge point matters: by standard practice the pipe must vent above the roofline, away from windows, so the concentrated soil gas dilutes into outdoor air instead of re-entering the house.

Other foundation types

Crawlspaces

Common in older Valley and Piedmont homes. The pro seals the crawlspace floor with a heavy plastic membrane and draws suction from underneath it — sub-membrane depressurization. Same principle, different surface. Homes around Winchester and Roanoke see this setup a lot.

Sump pits and drain tile

If the house has a sump, the pit is often the best suction point: the pro fits a sealed lid and draws from there, using the existing drain-tile loop to reach the whole slab.

Slab-on-grade and mixed foundations

Townhomes and additions often combine a slab here and a crawlspace there. Each foundation type may need its own suction point — one reason quotes differ between two houses on the same street, and a pricing factor covered in the cost guide.

What a licensed pro should actually do

1. Review your test result and the house’s foundation layout before quoting.
2. Run diagnostics where warranted — a communication test shows how well air moves under the slab and whether one suction point will do.
3. Seal accessible entry routes (sump lids, large cracks, open soil) as a supplement — sealing supports the system; it is never the system.
4. Size and mount the fan correctly, label the system, and fit the manometer.
5. Verify with a post-mitigation test that the level actually dropped — typically below 2 pCi/L for a well-built system. Don’t accept “trust me” without the retest.

Living with the system

• The fan runs continuously; electricity use is modest (roughly comparable to a light bulb left on).
• Glance at the manometer every month or two — if the fluid levels out, call for service.
• Fans typically carry around a five-year manufacturer warranty and are a straightforward replacement when they wear out.
• The EPA recommends re-testing every two years even with a system running — see the testing guide.