What Is Radon Mitigation? Systems, Cost, and Standards
What is radon mitigation comes up the moment a Front Range short-term radon test reads above 4 picocuries per liter (pCi/L), the EPA action level. Mitigation is the engineering process of reducing indoor radon concentrations to safer levels through a permanent installed system. The dominant approach in the United States is sub-slab depressurization (SSD), a method standardized under EPA Mitigation Standard ASD-1995. A typical Front Range SSD installation costs $1,000 to $2,500 and reduces indoor radon by 50 to 99 percent within 24 to 48 hours of activation. This guide summarizes EPA, CDC, and CDPHE guidance current as of 2026, walks through the components of a typical mitigation system, and explains the cost drivers and verification testing. Consult a certified radon professional for testing and your physician for any health concerns.
What is radon mitigation in plain language?
Radon mitigation is the installation of an engineered system that reduces indoor radon gas concentrations to below the EPA action level of 4 pCi/L, with the practical goal of getting as close to outdoor ambient levels (around 0.4 pCi/L) as the home’s construction allows. The systems work by intercepting radon gas before it enters the living space or by removing it from indoor air after entry. The dominant approach intercepts gas before entry by depressurizing the soil under the foundation.
Mitigation differs from radon testing. Testing measures the indoor radon concentration; mitigation reduces it. The two activities are sequential: an initial test confirms a problem, the mitigation system is installed, and a post-mitigation test verifies the reduction. The Front Range radon testing guide covers the testing side, and this article covers the mitigation engineering that follows when testing identifies elevated levels.
EPA Mitigation Standard ASD-1995
EPA published the Radon Mitigation Standard for Active Soil Depressurization (ASD-1995) in 1995, and it remains the dominant US technical standard for residential radon mitigation. ASTM E2121 is a closely related standard that some certified mitigation contractors reference. Together these standards define the engineering parameters for a sub-slab depressurization system: suction point placement, pipe sizing, fan capacity, exhaust location, sealing requirements, and labeling.
State radon programs typically require certified mitigation contractors to install systems that meet ASD-1995 specifications. Colorado Department of Public Health and Environment (CDPHE) maintains a list of certified mitigation professionals who hold National Radon Proficiency Program (NRPP) or National Radon Safety Board (NRSB) credentials. Both credential bodies require continuing education and field-testing competency on ASD-1995 installations.
Sub-slab depressurization (SSD): the dominant approach
Sub-slab depressurization works by creating a slight negative pressure under the concrete slab foundation that intercepts radon gas before it can enter the living space above. The system pulls air (and any soil gas including radon) from under the slab and exhausts it above the roof line, where it disperses harmlessly in the outdoor atmosphere.
A typical SSD system has six core components:
- Suction point — A core hole drilled through the concrete slab, typically 4 to 6 inches in diameter, that creates an access point into the gravel layer or soil under the foundation.
- Sub-slab gravel layer — Most modern construction includes a 4-inch gravel layer under the slab that provides a permeable pathway for soil gas. Older slabs may have less or no gravel.
- Perforated PVC pipe — A vertical pipe (typically 3-inch or 4-inch PVC) extends from the suction point upward through the conditioned space or a non-conditioned chase.
- Inline radon fan — A specialty radon mitigation fan (typically 40 to 90 watts, mounted in the non-conditioned section of the pipe) provides the negative pressure that drives the system.
- U-tube manometer — A simple pressure-monitoring device that shows the homeowner whether the fan is providing the designed pressure difference. A glance at the manometer fluid level confirms the system is working.
- Outdoor exhaust — The pipe terminates above the roof line in a location that meets EPA setback requirements from windows, doors, and adjacent occupied spaces.
The full system runs continuously, drawing roughly 40 to 90 watts of electricity. Annual operating cost is typically $30 to $90 in electricity. The radon fan has a typical service life of 5 to 12 years before replacement is required.
How quickly SSD reduces indoor radon
Most SSD installations show measurable reduction in indoor radon within 24 to 48 hours of fan activation. Full reduction to the system’s design level is typically reached within 2 to 4 weeks as the soil gas concentration under the slab stabilizes at the new equilibrium. A post-mitigation short-term radon test conducted 24 hours to 30 days after installation verifies the reduction. Most certified mitigation systems reduce indoor radon by 50 to 99 percent, with the typical reduction landing in the 80 to 95 percent range.
Typical Front Range mitigation cost
A standard SSD mitigation system installed in a Front Range single-family home in 2026 typically costs $1,000 to $2,500. The cost varies based on several factors:
- Foundation type (slab-on-grade, basement, crawlspace, or combination)
- Number of suction points required (most homes need one, larger homes need two or more)
- Routing complexity (whether the pipe can run through a non-conditioned chase or must penetrate finished spaces)
- Exhaust routing distance and complexity
- Additional features like alarmed fan monitoring or sealed sump covers
Slab-on-grade homes typically fall at the lower end of the range ($1,000 to $1,500). Basement homes are mid-range ($1,500 to $2,000). Crawlspace homes or homes with multiple foundation types often require sub-membrane depressurization for the crawlspace portion plus SSD for the basement portion, pushing total cost to $2,000 to $2,800.
The residential radon mitigation cost guide for the Front Range walks through the cost variables in more depth.
Post-mitigation verification testing
Verification testing is essential to confirm the mitigation system is producing the expected radon reduction. EPA and CDPHE both require certified mitigation contractors to provide post-mitigation test results to the homeowner, typically as part of the standard installation package.
The standard verification protocol uses a short-term radon test (48 to 96 hours, continuous monitor preferred) conducted no sooner than 24 hours after the mitigation system is fully operational. The test placement follows the same EPA protocols as initial radon testing: the lowest livable level, closed-house conditions, away from drafts and exterior walls. Test results documenting indoor radon below 4 pCi/L confirm the system is working as designed.
Ongoing monitoring after verification
Verification testing is the final step in the initial mitigation process, but it is not the last test the homeowner should ever conduct. EPA recommends retesting every 2 years for the life of the mitigation system, plus an additional test after any significant change to the home (basement renovation, foundation work, HVAC replacement, addition of new conditioned space). The retests confirm continued system effectiveness and catch any fan failures or pipe damage before they create extended elevated-radon exposure.
When SSD is not the right approach
Sub-slab depressurization works well for most slab-on-grade and basement foundations but may not be the right approach for every home. Crawlspace foundations typically use sub-membrane depressurization (SMD), which is similar in principle but uses a sealed plastic membrane laid over the crawlspace floor instead of a poured slab. Block-wall foundations sometimes use block-wall depressurization, which depressurizes the hollow cores of the block rather than the soil under the slab.
Homes with no gravel under the slab or with severely cracked or fragmented slabs may require multiple suction points or supplemental ventilation to reach acceptable indoor radon levels. A certified mitigation contractor evaluates the foundation during the initial site visit and recommends the appropriate system design.
How mitigation interacts with the home’s HVAC system
SSD mitigation is largely independent of the home’s HVAC system, which is one of its advantages. The system runs continuously regardless of furnace or AC operation, and it does not affect indoor air quality beyond the radon reduction itself. Some homes benefit from supplemental HVAC adjustments alongside mitigation, particularly homes with mechanical ventilation systems (HRV or ERV) that can be tuned to support the depressurization rather than work against it.
Combustion appliances (furnaces, water heaters, gas dryers) require attention during mitigation system design because depressurization in a tightly sealed home can occasionally interfere with proper draft of combustion gases. Certified mitigation contractors check combustion-appliance draft as part of post-installation verification, particularly in older homes with atmospheric-vented furnaces or water heaters.
What the mitigation installation process looks like
A typical SSD installation in a Front Range single-family home takes one day, with most certified contractors completing the work in 4 to 8 hours. The installation begins with a site evaluation: the contractor identifies the optimal suction-point location based on slab condition and gravel quality, plans the pipe routing through the home, and selects the exhaust termination point. Drilling the suction point through the slab takes 30 to 60 minutes and produces some dust, which the contractor contains with plastic sheeting. The PVC pipe is then installed and sealed at the slab penetration with a flexible polyurethane sealant rated for the application.
The pipe is routed upward through a closet, mechanical room, or other non-conditioned space until it exits through the roof or an exterior wall above the eave line. The radon fan is installed in the non-conditioned section of the pipe (most often in an attic, garage, or exterior installation) and wired to a dedicated electrical circuit. The manometer is mounted at the visible portion of the pipe in the basement or mechanical room. Final steps include sealing any visible foundation cracks or sump pump openings that would short-circuit the depressurization, labeling the system per ASD-1995 requirements, and conducting an operational test.
Why mitigation is worth the investment
The EPA estimates that radon exposure is the second-leading cause of lung cancer in the United States, after tobacco smoke, and the leading cause among non-smokers. CDC echoes that risk assessment. Mitigation reduces lifetime exposure for every occupant of the home, including future occupants who inherit the home through sale or transfer. The $1,000 to $2,500 one-time cost plus $30 to $90 annual electricity cost is small relative to the lifetime cancer risk reduction the system provides.
Many Front Range real-estate transactions now treat radon mitigation as a near-default inclusion when initial testing shows elevated levels. Buyer agents frequently request seller-paid mitigation in the inspection-objection response, and the cost is small enough relative to typical home values that most sellers accept rather than push back. That market norm has made certified mitigation contractors a routine part of the closing process across Douglas, Jefferson, El Paso, and Boulder counties. A buyer purchasing a home that already has a working mitigation system can verify continued operation with a quick manometer check and a post-purchase verification test.
References
- EPA consumer’s guide to radon reduction — US Environmental Protection Agency
- CDPHE radon program and certified mitigator list — Colorado Department of Public Health and Environment
- American Lung Association radon mitigation guidance — American Lung Association
Front Range homeowners with a recent radon test above 4 pCi/L can use our contact page to connect with a vetted CDPHE-certified mitigation contractor for a system design and quote.