Radon mitigation
Sub-slab depressurization, mitigation system install. We match you with up to 4 vetted local contractors who verify their license and insurance with our network.
Radon is the second-leading cause of lung cancer in the United States, after smoking. Roughly one in 15 US homes has elevated radon levels (above the 4.0 pCi/L EPA action level) — and the only way to know your level is to test. If your home tests high, mitigation is straightforward, effective, and almost always cheaper than homeowners expect.
This page covers what you need to know before scheduling: how radon testing works, what a "high" result means, the standard mitigation method (sub-slab depressurization), variations for different foundation types, what post-mitigation testing should show, and how to hire a certified mitigation specialist. We connect homeowners with NEHA/NRPP-certified radon mitigation specialists.
EPA action level: radon above 4.0 pCi/L (picocuries per liter) warrants mitigation. EPA recommends considering mitigation between 2.0 and 4.0 pCi/L. The unit pCi/L measures the concentration of radioactive radon gas — radon is invisible, odorless, and produces no immediate symptoms. The only way to know your home's level is to test.
How radon testing works
Radon enters homes from the soil beneath the foundation. Concentrations vary by geology (uranium-rich rock formations create more radon), foundation type (basements and slab-on-grade more exposed), and home tightness (well-sealed homes can accumulate higher levels indoors).
Short-term test (2-7 days): a passive test kit (charcoal canister or alpha-track detector) placed in the lowest livable area of the home. Sealed and sent to a lab. Result back in 1-2 weeks. Cheap (often $15-30), good for initial screening.
Long-term test (90+ days): a passive detector left in place for 90 days to a year. Smooths out short-term fluctuations from weather and HVAC. More accurate than short-term tests for assessing actual long-term exposure.
Continuous radon monitor (CRM): an electronic device that records hourly readings, often used by professionals during real-estate transactions. Shows time-of-day and weather-related variations. Some homeowners now own consumer-grade CRMs for ongoing monitoring (Airthings, Ecosense).
Real-estate testing: a 48-72 hour test under closed-house conditions, typically performed by a certified inspector during the home-purchase contingency period. Specific testing protocols (closed-house conditions, no recent HVAC changes) apply.
The right testing decision depends on context. For new homeowners, start with a short-term test. If the result is borderline (2-4 pCi/L), follow up with a long-term test. If the result is high (above 4 pCi/L), confirm with a second short-term test before scheduling mitigation — false positives happen, though most short-term high results are real.
Sub-slab depressurization — the standard mitigation method
For homes with basement or slab-on-grade foundations, the standard radon mitigation method is sub-slab depressurization (SSD). The technique creates a slight vacuum under the slab that captures radon-laden soil gas before it can enter the home.
How it works: a 4-inch PVC pipe is installed through the slab, typically through an existing crack or a small drilled hole. The pipe runs up through the home (or up the exterior of the home) to a fan installed in an attic or on the exterior. The fan runs continuously, pulling air from below the slab through the pipe and venting it above the roofline. The fan creates negative pressure in the soil under the slab, which prevents radon-laden gas from entering the home through cracks or porous concrete.
The install: typically 1 day for a standard mitigation. Requires drilling through the slab (1 small hole), running the PVC pipe, sealing slab cracks and the sump pump cover (if applicable), installing the fan, and venting through the roof or up the exterior wall. The system has a U-tube manometer (a simple pressure gauge) installed at the pipe to confirm ongoing operation.
Variations for different foundations:
Crawlspace homes: a different technique called crawlspace depressurization (or sub-membrane depressurization). A vapor barrier is sealed across the crawlspace floor, and the fan pulls air from under the membrane. Effectively the same physics applied to a different foundation.
Slab-on-grade with no basement: standard SSD works, with the fan typically installed outside or in a garage rather than in an attic.
Multi-foundation homes (combination basement + crawlspace + slab): the mitigation specialist designs a system that captures gas from each foundation type. May require multiple suction points.
Post-mitigation testing — what passing looks like
After install, the system needs to be tested to confirm it's actually working:
- Wait at least 24 hours after install to allow the fan to draw down sub-slab pressure
- Run a new short-term radon test (typically 48-72 hours) under closed-house conditions
- Target: post-mitigation levels below 2.0 pCi/L (well below the 4.0 EPA action level), which most properly-installed systems achieve
- If post-mitigation results are still above 4 pCi/L: the system needs adjustment — usually a second suction point, more aggressive sealing, or a stronger fan
- Re-test every 2 years going forward — fans wear out, slab cracks open over time, and the manometer can give false confidence if the fan motor degrades slowly
Common radon mitigation failures
Patterns that show up in 1-3 year follow-ups:
- Single suction point on a foundation that needs multiple — large basements with internal walls often need 2-3 suction points to capture the entire footprint
- Slab cracks not properly sealed — radon leaks around the SSD system instead of being captured
- Sump pump cover not sealed — radon enters through the sump pit
- Fan undersized for the soil permeability — system creates inadequate negative pressure
- Fan installed indoors below the highest occupied floor — code violation in most jurisdictions; if the pipe leaks, it can re-introduce radon to living space
- Vent pipe terminating below roofline or near windows — radon recirculates back into the home
- No post-mitigation testing — homeowner assumes the system is working without verification
- Manometer not monitored over time — fan failure goes undetected for months or years
Cost variables and incentives
Radon mitigation cost depends on foundation type, home complexity, and whether radon-resistant features were built in originally. Homes built after EPA radon standards became common (mid-1990s in some markets, later elsewhere) often have passive radon-ready piping that just needs a fan added — much simpler than retrofitting a non-radon-ready foundation.
The install variables:
Number of suction points needed: a 1,500 sq ft slab is usually one suction point; a 3,000 sq ft basement with internal walls might need 2-3.
Foundation accessibility: visible slab vs finished basement (mitigation specialist has to coordinate with finishing).
Vent routing: short interior run vs long exterior chase requiring conduit and weatherproofing.
Fan choice: standard fans for typical loads, higher-suction fans for tight or rocky soil conditions.
Federal: no specific federal radon mitigation tax credit exists currently. Mitigation can sometimes be expensed as a medical-related improvement if a household member has been diagnosed with lung disease related to radon, but this is unusual and requires CPA review.
State and utility: some state energy-efficiency programs include indoor air quality measures. EPA periodically funds state radon programs; check your state radon office for current programs.
Real estate: sellers commonly offer mitigation as part of contract negotiations when a buyer's test comes back high. The seller-paid mitigation is typically simpler than negotiating credits or remediation contingencies.
Frequently asked questions
How do I know if my home has high radon?▾
The only way is to test. Radon is invisible, odorless, and produces no immediate symptoms. Short-term tests (2-7 days) are cheap ($15-30) and good for initial screening; you place the kit in the lowest livable area, wait the required time, and mail it to a lab. If results come back high (above 4 pCi/L), confirm with a second test before scheduling mitigation. New homeowners should test in the first year of occupancy regardless of how the previous owner's tests came back — radon levels can shift over time.
What's the EPA action level?▾
EPA recommends mitigation for any home testing above 4.0 pCi/L (picocuries per liter). Between 2.0 and 4.0 pCi/L, EPA recommends considering mitigation. Below 2.0 pCi/L is the practical floor — most outdoor radon levels are around 0.4 pCi/L, and getting below that level indoors is impossible. The 4.0 pCi/L action level corresponds roughly to lung cancer risk equivalent to a non-smoker living in a home with that level for a lifetime.
How does sub-slab depressurization actually work?▾
A 4-inch PVC pipe is drilled through the slab and connected to a continuously-running fan that vents above the roofline. The fan creates a slight vacuum under the slab, pulling radon-laden soil gas through the pipe and out before it can enter the home through cracks or porous concrete. The system runs 24/7 (the fan is always on); a U-tube manometer at the pipe shows the system is working. Properly designed systems reduce indoor radon by 50-99%, typically getting homes from 8-12 pCi/L down to below 2 pCi/L.
How long does mitigation install take?▾
Typically 1 day for a standard sub-slab depressurization system. Crawlspace mitigation takes 1-2 days because the membrane install is more involved. Multi-foundation homes (combination basement + crawlspace) can take 2-3 days. Most installs include slab crack sealing, sump pump sealing if applicable, fan placement, vent routing, and manometer install. Post-install you wait 24 hours before re-testing.
Will the system reduce my radon levels?▾
A properly installed sub-slab depressurization system typically reduces indoor radon by 50-99%. Most homes go from initial levels of 8-15 pCi/L down to below 2 pCi/L after mitigation. If post-mitigation testing shows levels still above 4 pCi/L, the system needs adjustment — additional suction points, more aggressive sealing, or a stronger fan. The mitigation specialist should warranty their work to achieve below 4.0 pCi/L on post-install testing.
Does the fan need to run all the time?▾
Yes. The fan creates the pressure differential that prevents radon from entering the home. Turning it off lets radon levels rise back to pre-mitigation levels within hours to days. Modern fans use 30-90 watts continuously, similar to a single small lamp. Annual electricity cost is typically $30-100 depending on local rates.
How long do mitigation systems last?▾
The fan typically lasts 5-10 years; the rest of the system (PVC pipe, sealing, manometer) lasts the life of the home. When the fan fails, you replace just the fan ($150-400 plus install). The manometer should be checked monthly to confirm the system is working — if both the U-tube columns are equal, the fan has failed and needs replacement. Re-testing every 2 years is recommended even with a working manometer.
How do I find a vetted radon mitigation specialist?▾
Use the form on this page. We match you with NRPP-certified mitigation specialists with current insurance verified at network admission.