The basic idea: change the air pressure under your house
Radon enters homes because the air inside a house is usually at slightly lower pressure than the soil gas beneath it. Warm indoor air rising, exhaust fans, and dryers all contribute to this "stack effect", which pulls soil gas, and the radon in it, through cracks, joints, pipe penetrations, sump pits and bare crawlspace soil.
Modern radon mitigation reverses that relationship. Instead of trying to plug every crack (which never fully works), a system creates a small vacuum underneath the foundation. Soil gas gets pulled into a pipe and vented outdoors above the roofline, where it quickly dilutes, before it can enter the living space. EPA calls this approach soil suction or active soil depressurization, and it generally prefers methods that keep radon from getting in over methods that try to remove it after it's inside.
The parts of a typical system
- Suction point: a hole cored through the slab with a small pit dug beneath it, or a connection under a crawlspace membrane or sump lid.
- Vent pipe: usually PVC, routed either outside along an exterior wall or inside through a garage, closet or attic, ending above the roof edge.
- Radon fan: an in-line fan rated for continuous duty, mounted outside the living space (exterior wall, attic or garage) so any leak in the pressurized pipe stays out of the home.
- Manometer: a U-tube gauge on the pipe that shows the system is pulling suction. It's your at-a-glance health check.
- Sealing: caulk and foam at major cracks, slab joints, pipe penetrations and the sump, so the system pulls from the soil rather than from your basement air.
- Label: a system label with install information, often placed near the manometer or electrical panel.
System types by foundation
Sub-slab depressurization (basements and slab-on-grade)
This is the workhorse of radon mitigation and the most common system on Upstate slab and basement homes. One or more suction points are installed through the slab. How many depends on what's underneath: gravel lets air move freely, so a single point can cover a large area, while the dense red clay common across the Piedmont can need extra points or a higher-suction fan. Installers often do a quick pressure field extension test, drilling small holes and checking for vacuum across the slab, to confirm coverage.
Sub-membrane depressurization (crawlspaces)
Many older Greenville and Easley homes, and plenty of newer ones, sit over crawlspaces with bare or partially covered soil. Here the installer lays a durable plastic membrane over the crawlspace floor, overlaps and seals the seams, seals it to the foundation walls and piers, then installs a suction point beneath the membrane. The fan draws radon from under the plastic before it can rise into the house.
Encapsulation vs. sub-membrane depressurization: full crawlspace encapsulation (heavier liners, sealed vents, sometimes a dehumidifier) is mainly a moisture and comfort upgrade. It can pair well with a radon system, but for radon the key piece is the suction under the membrane. Ask any contractor to spell out which one they're quoting.
Sump pit suction
If your basement has a sump pit tied into drain tile around the foundation, that drain tile can carry suction around the perimeter. The installer fits an airtight, removable lid with the vent pipe passing through it. It's an efficient design when the drain tile loop is continuous, and the pump stays serviceable.
Combination and other methods
Houses with mixed foundations, such as a basement plus a slab addition or a crawlspace plus a garage slab, often get suction points in each area tied into one fan. Less common options include block-wall suction for hollow concrete-block foundation walls, and passive systems (a vent pipe with no fan) that are sometimes built into new construction. EPA's guide notes that passive systems reduce radon less than active ones, so a passive stack is typically designed so a fan can be added if testing shows it's needed.
Sealing cracks alone, or simply adding ventilation, is not a reliable stand-alone fix. EPA notes that sealing by itself hasn't been shown to lower radon significantly or consistently.
The install process, step by step
- Start from a test result. EPA recommends fixing a home at 4 pCi/L or higher and considering it between 2 and 4 pCi/L. No result yet? Get radon testing in Greenville first.
- Site visit and design. The installer reviews the foundation, sump, crawlspace, attic access and roofline, and decides on suction points, pipe route and fan location.
- Written proposal. You should see the design, what gets sealed, the fan model and warranty, and whether the post-mitigation test is included. See what drives mitigation cost.
- Installation day. Core the slab or lay the membrane, build the suction pit, route and support the pipe, mount the fan, have the electrical connection made to code, seal openings, install the manometer and label, and clean up. Most single-family installs take a day.
- Startup check. The installer confirms suction on the manometer and checks for backdrafting of fuel-burning appliances where relevant.
- Post-mitigation test. Covered below.
Post-mitigation testing: proof it works
A system isn't finished until a test says so. EPA advises a short-term test no sooner than 24 hours after the system starts running and no later than 30 days, under the same closed-house conditions as any radon test. With today's technology, EPA says most homes can be brought down to 2 pCi/L or below. After that:
- Check the manometer occasionally. If the liquid levels even out, the fan may have stopped.
- Retest about every two years, and after major renovations, a basement finish or HVAC changes.
- If you sell, a recent low result plus the system paperwork reassures buyers (real estate tips).
Choosing a qualified installer
EPA recommends using a qualified radon mitigation professional. Two national programs certify radon professionals in the U.S.: the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB). Both publish searchable directories, so you can confirm a credential yourself. Also check with the SC Department of Environmental Services radon program for current state guidance.
- Ask for the installer's NRPP or NRSB certification number and verify it.
- Ask whether they follow the current ANSI/AARST standard for radon mitigation in homes.
- Get the design in writing: suction points, pipe route, fan location, sealing.
- Confirm who runs the post-mitigation test, and when.
- Get fan and performance warranties in writing.
- Ask for proof of liability insurance.
We'll answer all of these on the phone before you decide. Call (864) 555-0100.
Where we install
- Greenville
- Greer
- Simpsonville
- Mauldin
- Taylors
- Travelers Rest
- Easley
- Fountain Inn
- Five Forks
- Spartanburg
- Anderson
- the wider Upstate
Back to radon mitigation in Greenville, SC · Learn why Greenville County is EPA Zone 1.