If your radon test comes back elevated, the good news is that radon mitigation is one of the more straightforward “health-protection” home improvements. Radon is a gas that can enter buildings from the soil, and mitigation systems are designed to interrupt that pathway—either by changing pressure under the home, sealing and redirecting soil gas, or improving controlled ventilation. In most homes, modern mitigation methods can significantly reduce radon levels. (Source: EPA – https://www.epa.gov/radon; Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
This is a pillar article: it’s intentionally detailed. We’ll cover when mitigation is recommended, the major system types (slab, crawlspace, basement), what a proper installation looks like, cost drivers, how to choose a qualified contractor, how to verify results, and how to maintain a system over time. We’ll cite authoritative sources throughout, primarily from the U.S. Environmental Protection Agency (EPA) and other recognized organizations. (Source: EPA – https://www.epa.gov/radon)
Table of Contents
- What radon mitigation is (in plain English)
- When you should mitigate (EPA action level and “consider fixing”)
- How mitigation works: the building-science basics
- Most common system: Sub-slab depressurization (SSD)
- Mitigation for crawlspaces (sub-membrane systems)
- Other mitigation approaches (and when they’re used)
- What a good installation includes (components checklist)
- How much mitigation costs (and what changes the price)
- How to choose a qualified radon contractor
- After mitigation: testing, targets, and verification
- Living with a system: maintenance, fan lifespan, troubleshooting
- Radon-resistant new construction (RRNC) and “radon-ready” homes
- Myths and FAQs
- Sources and further reading
1) What radon mitigation is (in plain English)
Radon mitigation means reducing radon levels inside a building. Radon is a naturally occurring radioactive gas that can seep into homes from the soil. Mitigation systems are designed to either (1) keep radon from entering, (2) capture it before it enters living space, or (3) dilute and exhaust it safely. The goal is to reduce long-term exposure and therefore reduce lung cancer risk. (Source: EPA – https://www.epa.gov/radon; Source: CDC – https://www.cdc.gov/radon/about/index.html)
Most residential mitigation systems are not “filters.” They’re pressure and airflow systems—more like a controlled exhaust pathway for soil gas. That’s why properly installed systems can be consistently effective, and why sealing alone (while helpful) is rarely the entire solution. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
2) When you should mitigate (EPA action level and “consider fixing”)
The EPA recommends taking action to reduce radon when the radon level is 4.0 pCi/L or higher. EPA also states there is no known safe level of radon exposure and encourages homeowners to consider reducing radon when levels are between 2.0 and 4.0 pCi/L. (Source: EPA – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean)
How you make decisions also depends on test type. Short-term tests are useful but can vary with weather and house conditions. Long-term tests (90 days or more) typically better represent the home’s annual average. EPA provides decision guidance in its Citizen’s Guide. (Source: EPA Citizen’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Practical rule: If you have a confirmed result at or above 4.0 pCi/L, mitigation is the standard next step. If you’re between 2.0 and 4.0, mitigation is optional but commonly chosen—especially if you spend time in the basement, if anyone smokes, or if you simply want to reduce risk. (Source: EPA – https://www.epa.gov/radon; Source: CDC – https://www.cdc.gov/radon/features/reduce-radon.html)
3) How mitigation works: the building-science basics
Radon primarily enters a home as part of soil gas. Houses are rarely perfectly sealed from the ground. Tiny cracks, gaps, joints, sump pits, pipe penetrations, and porous foundation features can allow soil gas to enter. Many homes also create slight pressure differences that “pull” air from the soil into the building (stack effect, exhaust fans, HVAC operation, and duct leakage can contribute). (Source: EPA Building Radon Out (PDF) – https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf; Source: EPA Citizen’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
Most effective mitigation systems work by changing that pressure relationship. Instead of your house pulling air from the soil, the mitigation system pulls soil gas from beneath the foundation and vents it safely above the roofline, where it dilutes outdoors. This is the logic behind the most common method: sub-slab depressurization. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
4) Most common system: Sub-slab depressurization (SSD)
Sub-slab depressurization (SSD) is the most widely used radon mitigation method for homes with basements and slab-on-grade foundations. It typically involves drilling a small suction pit through the slab, installing PVC piping, and using a continuously operating fan to draw soil gas from under the slab and vent it above the roofline. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Why SSD works so well
SSD works because it controls the pressure field under the slab. If the fan creates a lower pressure beneath the slab than the indoor space, soil gas (including radon) is pulled into the system piping instead of leaking into the home. In many homes, this can reduce radon substantially, often below 2.0 pCi/L. EPA notes that with today’s technology, radon levels can be reduced in most homes. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Where the suction point goes
The contractor typically creates a small cavity (suction pit) under the slab so air can flow into the pipe. Some homes need more than one suction point depending on slab size, foundation layout, and sub-slab material. A well-designed system aims for effective pressure communication under the slab. (Source: EPA Building Radon Out (PDF) – https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf)
What you’ll see after installation
Most SSD systems have visible PVC piping (often routed through a garage, utility area, closet, or along an exterior wall) and a fan located outside the conditioned living space (commonly in the attic, garage, or exterior). Proper venting above the roofline is important for safe dispersion. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
5) Mitigation for crawlspaces (sub-membrane systems)
Crawlspaces are a common radon entry pathway because they often expose the building to soil gas directly (especially if the crawlspace floor is bare earth). A common mitigation method is sub-membrane depressurization: the contractor installs a heavy-duty plastic membrane (liner) across the crawlspace floor, seals it at seams and edges, and then draws soil gas from beneath the membrane using a vent pipe and fan—similar in concept to SSD. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
In some cases, crawlspace ventilation strategies are discussed, but modern best practice often prefers sealed-liner depressurization because it directly controls soil gas entry. The right approach depends on climate, crawlspace design, and building conditions. (Source: EPA – https://www.epa.gov/radon)
6) Other mitigation approaches (and when they’re used)
Block-wall suction / drain tile suction
Some foundations have hollow block walls or perimeter drain tiles that can act as radon pathways. In those cases, mitigation may use suction from the block wall or drain tile system, sometimes combined with sub-slab suction. The objective is the same: create a controlled low-pressure route for soil gas to leave the foundation area without entering the home. (Source: EPA Consumer’s Guide to Radon Reduction (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Heat recovery ventilators (HRVs) and ventilation approaches
In certain situations, increased ventilation can reduce indoor radon by diluting it, and HRVs can help exchange indoor/outdoor air while retaining heat energy. These approaches may be used when sub-slab options are limited, as part of a broader strategy, or for certain building types. However, ventilation alone is not always as consistent as soil depressurization for typical radon entry patterns. (Source: EPA – https://www.epa.gov/radon; Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Sealing and caulking
Sealing cracks and openings is commonly performed as a supporting measure (and it can improve system performance), but EPA generally does not treat sealing alone as a primary mitigation method because radon can enter through many pathways and pressure differences can still pull soil gas in. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
7) What a good installation includes (components checklist)
While every house is different, most quality mitigation projects include the same core components and “proof points.” Here’s what homeowners should expect to see.
Core components
- Suction point(s): typically through slab or beneath crawlspace liner
- Piping: usually PVC vent pipe routed to a safe discharge point
- Radon fan: creates suction; typically installed outside living space
- Discharge: vented above roofline or other approved location for dilution
- Sealing (supportive): cracks, sump lids, penetrations as appropriate
- System monitor: often a manometer (“U-tube”) or other indicator showing fan operation
EPA consumer guidance discusses common radon reduction methods and emphasizes verifying that systems are working and retesting after installation. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Comfort and safety considerations
A proper system design also considers noise, condensation management in piping, aesthetics, and ensuring the fan and discharge placement meet guidance for safe venting. If combustion appliances are present, professional mitigators may also consider backdrafting risks and overall house pressure interactions. (Source: EPA Building Radon Out (PDF) – https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf)
8) How much mitigation costs (and what changes the price)
Radon mitigation cost varies by region and home design, but EPA commonly cites a typical range for many homes. Costs can be influenced by foundation type, routing difficulty, number of suction points required, crawlspace liner work, electrical needs, and whether extra sealing or sump modifications are needed. (Source: EPA Building Radon Out (PDF) – https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf)
As a broad homeowner expectation, many systems fall in the hundreds to low-thousands range, with some homes (complex foundations or crawlspaces) costing more. EPA’s construction guidance notes that adding radon-resistant features during new construction is often cheaper than retrofitting later—one reason radon-resistant new construction is promoted in higher-potential areas. (Source: EPA Building Radon Out (PDF) – https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf; Source: EPA RRNC basics – https://www.epa.gov/radon/radon-resistant-construction-basics-and-techniques)
Cost drivers (real-world)
- Foundation type: basement vs slab vs crawlspace
- Access and routing: hard-to-route vent runs (finished spaces, long routes)
- Multiple suction points: larger footprints or complex slabs may need more
- Crawlspace liner work: sealing and durable membrane installation adds labor
- Electrical: fan power requirements and code-compliant wiring
- Local market: labor rates and contractor availability
9) How to choose a qualified radon contractor
Mitigation is a specialized trade. You want someone who follows recognized methods and will verify performance with post-mitigation testing. Many homeowners look for professionals certified by recognized credentialing organizations such as NRPP or NRSB, and many professionals follow ANSI/AARST standards in their practice. (Source: NRPP – https://nrpp.info/; Source: NRSB – https://nrsb.org/; Source: AARST – https://aarst.org/)
Questions to ask before hiring
- What mitigation method are you recommending for my foundation, and why?
- Where will the suction point(s), fan, and discharge be located?
- Will you install a system monitor (manometer) so I can confirm the fan is running?
- What sealing or sump modifications will be included?
- How and when should I test after mitigation to confirm results?
- What kind of warranty is included for workmanship and fan performance?
EPA encourages consumers to ensure mitigation is properly done and verified by testing afterward. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
10) After mitigation: testing, targets, and verification
Post-mitigation testing is non-negotiable. The only way to confirm the system worked is to test again. EPA consumer guidance stresses that you should test your home after a radon reduction system is installed to confirm the radon level has dropped. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
What level should you aim for?
EPA’s action level is 4.0 pCi/L, but many homes can be reduced further, and EPA encourages considering reductions even below 4.0 because there is no known safe level. Many homeowners aim for below 2.0 pCi/L when feasible. (Source: EPA action level explanation – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean; Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Where and how to test after mitigation
Test the lowest lived-in level (often the basement if it’s used) and follow test instructions carefully. If you want a strong representation of average exposure, use a long-term test, but short-term confirmation tests are also commonly used immediately after installation depending on context. (Source: EPA Citizen’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf)
11) Living with a system: maintenance, fan lifespan, troubleshooting
Mitigation systems are usually low-maintenance, but they are not “set and forget forever.” The radon fan is a mechanical device that runs continuously. Over time, fans can fail, condensate can become an issue in some climates, and renovations can change house pressure dynamics. EPA recommends retesting periodically and after major changes. (Source: EPA retesting guidance – https://www.epa.gov/radon/how-often-should-i-testretest-my-home-radon)
Simple owner checks
- Look at the system monitor: many systems include a manometer showing the fan is creating suction.
- Listen for unusual fan noise: sudden changes can signal wear.
- Retest every so often: especially if your last test was years ago or if you remodel.
If your post-mitigation test is still high
Don’t assume failure means the approach is wrong—many times it means the system needs adjustment: additional suction points, sealing improvements, fan sizing changes, or addressing a specific entry pathway (like a sump lid or a block wall). Follow up with your contractor and test again after changes. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
12) Radon-resistant new construction (RRNC) and “radon-ready” homes
If you are building a home (or buying new construction), radon-resistant new construction (RRNC) is worth understanding. RRNC uses features like a gas-permeable layer beneath the slab, plastic sheeting, sealing, vent piping, and a junction box for a future fan. Some homes are built “radon-ready” with passive features that can be upgraded to an active system if testing shows elevated levels. (Source: EPA RRNC basics – https://www.epa.gov/radon/radon-resistant-construction-basics-and-techniques; Source: EPA Building Radon Out (PDF) – https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf)
RRNC doesn’t eliminate the need for testing. EPA still recommends testing because site conditions and final building behavior determine actual radon levels. RRNC just makes mitigation easier and cheaper if a fan needs to be added. (Source: EPA – https://www.epa.gov/radon)
13) Myths and FAQs
Myth: “A fan and pipe in the basement is dangerous.”
A properly installed system is designed to vent radon safely outdoors and reduce indoor levels. The system’s purpose is risk reduction, and it should be verified by post-mitigation testing. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
Myth: “Opening windows fixes radon.”
Opening windows can temporarily reduce radon by increasing ventilation, but it’s not a reliable long-term solution and doesn’t address the underlying soil gas entry mechanisms. Mitigation systems are designed for consistent reduction. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
FAQ: “Will mitigation increase my energy bills?”
Many mitigation systems use an electric fan that runs continuously, so there is some operating cost. The amount varies by fan and local electricity rates. If ventilation-based strategies are used, energy impacts can be higher. Discuss expected operating cost with your contractor. (Source: EPA – https://www.epa.gov/radon)
FAQ: “Can I install mitigation myself?”
Some homeowners attempt DIY mitigation, but correct design and safe vent routing matter. EPA guidance is written with consumers in mind and emphasizes verified reduction through testing. For most people, hiring a qualified professional is the most reliable approach—especially if the home has complex foundation features or combustion appliances. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)
FAQ: “If I mitigate, do I still need to test?”
Yes. Test immediately after installation to confirm results, and retest periodically or after major changes. This is how you know the system is still delivering the protection you installed it for. (Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf; Source: EPA retesting guidance – https://www.epa.gov/radon/how-often-should-i-testretest-my-home-radon)
Sources and further reading
- EPA – Radon main hub: https://www.epa.gov/radon
- EPA – Consumer’s Guide to Radon Reduction (PDF): https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf
- EPA – A Citizen’s Guide to Radon (PDF): https://www.epa.gov/sites/default/files/2016-12/documents/2016_a_citizens_guide_to_radon.pdf
- EPA – Building Radon Out (PDF): https://www.epa.gov/sites/default/files/2014-08/documents/buildradonout.pdf
- EPA – Action level explanation: https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean
- EPA – How often to test/retest: https://www.epa.gov/radon/how-often-should-i-testretest-my-home-radon
- NRPP (certified professionals): https://nrpp.info/
- NRSB (certified professionals): https://nrsb.org/
- AARST (standards and professional org): https://aarst.org/
- CDC – Radon overview: https://www.cdc.gov/radon/about/index.html
Bottom line
Radon mitigation is about controlling a pathway. If radon is entering from the soil, the most reliable solution is usually a system that captures soil gas and vents it safely outdoors. EPA recommends mitigating at 4.0 pCi/L and encourages considering reductions even below that because there is no known safe level of radon exposure. Test, mitigate if needed, and always retest to confirm performance. (Source: EPA – https://www.epa.gov/radon/what-epas-action-level-radon-and-what-does-it-mean; Source: EPA Consumer’s Guide (PDF) – https://www.epa.gov/sites/default/files/2016-12/documents/2016_consumers_guide_to_radon_reduction.pdf)