Radon Mitigation Techniques: A Catalog by Foundation
Radon mitigation techniques span more than the single sub-slab depressurization (SSD) installation that comes to mind most often. Different foundation types and different deterioration patterns call for different engineering approaches. SSD is the dominant technique for slab-on-grade and basement foundations. Sub-membrane depressurization (SMD) handles crawlspaces. Block-wall depressurization addresses the hollow cores of concrete block foundations. Sump-cover sealing and soil-gas membrane systems serve as targeted additions. This guide summarizes EPA, CDC, and CDPHE guidance current as of 2026 and walks through the technique catalog with a decision framework for matching technique to foundation type. Consult a certified radon professional for testing and your physician for any health concerns.
What radon mitigation techniques are available?
EPA recognizes several primary and supplemental radon mitigation techniques in its Mitigation Standard ASD-1995 and supporting technical guidance. The primary techniques actively reduce indoor radon by intercepting soil gas before it enters the living space. The supplemental techniques address specific entry pathways or work alongside a primary system to improve overall effectiveness.
The seven techniques covered in this guide are:
- Sub-slab depressurization (SSD) — primary technique for slab and basement foundations
- Sub-membrane depressurization (SMD) — primary technique for crawlspaces
- Block-wall depressurization — primary technique for hollow-core block foundations
- Sump-cover sealing with active fan — primary or supplemental, depending on configuration
- Soil-gas membrane systems — primary technique for some new construction
- Foundation crack sealing — supplemental only, never standalone
- HRV/ERV ventilation — supplemental or standalone for marginally elevated radon
The Front Range radon testing guide covers the testing that identifies which homes need mitigation, and this article covers the technique catalog that informs the system design.
Sub-slab depressurization (SSD)
SSD is the dominant US residential mitigation technique because most US homes have either a poured concrete slab or a basement floor. The technique creates negative pressure under the slab using a continuously running radon fan that pulls soil gas through a sub-slab gravel layer and exhausts it above the roof line.
SSD works best when several conditions are met:
- The slab has a permeable gravel layer underneath (4 inches of clean gravel is the modern code standard)
- The slab is in reasonably intact condition (large cracks or fragmented sections reduce effectiveness)
- Sump pits, floor drains, and other slab penetrations are sealed to prevent short-circuiting
- A single suction point provides adequate coverage (larger homes may need two or more suction points)
Typical Front Range SSD installation costs $1,000 to $2,000. Annual electricity cost runs $30 to $90. Reduction effectiveness typically lands in the 80 to 95 percent range, with most properly designed systems bringing indoor radon below 2 pCi/L. The comprehensive radon mitigation overview covers SSD installation details and post-mitigation verification testing.
Sub-membrane depressurization (SMD)
SMD is the crawlspace equivalent of SSD. The technique uses a sealed plastic membrane (typically 10-mil or thicker polyethylene) laid over the crawlspace floor and sealed at the perimeter walls. A radon fan pulls air from under the membrane and exhausts it above the roof line, creating the negative pressure needed to intercept soil gas before it enters the living space above.
SMD installations typically include:
- Full-coverage 10-mil or 12-mil polyethylene membrane sealed at every joint
- Perimeter sealing at the crawlspace walls (typically with butyl tape and mechanical fasteners)
- Sealed penetrations for plumbing, electrical, and structural elements that pass through the membrane
- A suction point and PVC pipe routed up through the home or along the exterior
- An inline radon fan in the non-conditioned section of the pipe
SMD typically costs $1,500 to $3,000 for a Front Range crawlspace, depending on size and access. Reduction effectiveness is similar to SSD (80 to 95 percent) when the membrane is properly sealed. A poorly sealed membrane allows soil gas to bypass the system and substantially reduces effectiveness.
Encapsulation as a parallel benefit
A properly installed SMD system effectively encapsulates the crawlspace, which delivers several side benefits beyond radon reduction. Moisture migration from soil into the home is reduced, which helps with mold prevention and structural moisture control. Pest entry pathways are largely sealed. Indoor humidity becomes easier to control because the unsealed soil floor no longer acts as a humidity source. Many Front Range homeowners install SMD primarily for radon and discover the moisture-control side benefits over the following years.
Block-wall depressurization
Block-wall depressurization addresses the specific problem of soil gas entering through the hollow cores of concrete block foundation walls. The technique creates negative pressure inside the hollow cores using a radon fan connected to one or more suction points drilled into the block wall.
The technique is most common in older Front Range homes (pre-1970) and in homes in areas of the Midwest where block-wall basements were standard construction. Concrete block has dozens of vertical voids that connect to the soil at the footer level and can act as a chimney for soil gas. Without depressurization, those voids deliver soil gas directly into the basement living space.
Block-wall depressurization is sometimes used as the primary mitigation technique in homes where SSD is impractical, and sometimes used as a supplement to SSD in homes where significant block-wall entry is documented. Installation cost is similar to SSD ($1,200 to $2,500), and combined SSD-plus-block-wall systems can run $2,500 to $4,000.
Sump-cover sealing with active fan
Sump pits are a common radon entry pathway in homes with perimeter drain systems. The unsealed sump pit acts as a direct opening between the soil and the basement living space. Sealing the sump pit with an airtight cover and tying it to a radon fan converts the pit from an entry pathway into a deliberate suction point.
A typical sealed-sump radon system includes:
- An airtight sump cover with sealed access ports for the discharge pipe and electrical wiring
- A radon fan connected to the sealed sump cover
- A PVC discharge pipe routed up through the home and exhausted above the roof line
- A manometer for ongoing pressure monitoring
Sump-cover sealing alone (without active depressurization) reduces some radon entry but is rarely sufficient as a standalone mitigation. Adding the active fan converts the sump into the primary mitigation technique for the entire home. Combined cost typically runs $1,200 to $2,500.
Soil-gas membrane systems
Soil-gas membrane systems are most often used in new construction rather than retrofit. The technique places a continuous radon-barrier membrane under the slab during construction, with sealed penetrations for plumbing and electrical, plus a passive vent stack that can be activated with a radon fan if post-construction testing shows elevated levels.
Many Front Range new-construction homes built since 2010 include radon-resistant construction features under the International Residential Code (IRC) Appendix F. The features typically include:
- A 4-inch sub-slab gravel layer
- A 6-mil polyethylene soil-gas retarder over the gravel
- A passive PVC vent stack from the gravel layer up through the roof
- Electrical rough-in at the vent stack location for future fan installation if needed
If post-construction testing shows elevated radon, activating the system by installing a radon fan on the existing passive stack is straightforward and typically costs $300 to $600. New-construction homes with these features are often the easiest mitigation projects in the Front Range market.
Foundation crack sealing
Crack sealing is a supplemental technique that should never be used as the standalone mitigation. Sealing visible foundation cracks, slab joints, and other openings reduces some radon entry but rarely brings indoor levels below the action threshold by itself. Cracks are also dynamic: new cracks form as the foundation settles and existing seals can fail over time.
The right role for crack sealing is as a complement to an active mitigation system. Sealing cracks reduces short-circuiting of the SSD or SMD system, which improves overall effectiveness. A certified mitigation contractor typically performs crack sealing as part of a comprehensive installation rather than as a separate service.
Decision framework: matching technique to foundation
The right technique depends primarily on foundation type and condition:
- Slab-on-grade with gravel layer — SSD as the primary technique. Single suction point usually sufficient.
- Full basement with poured concrete walls — SSD as the primary technique. Sump-cover sealing supplemental if sump pit is present.
- Crawlspace — SMD as the primary technique. Membrane sealing is critical to effectiveness.
- Mixed foundation (basement plus crawlspace) — Combined SSD plus SMD, with shared exhaust where layout allows.
- Hollow-core block-wall basement — SSD plus block-wall depressurization, or block-wall depressurization alone in some cases.
- New construction with passive stack — Activate existing passive system with radon fan installation.
- Marginally elevated radon (5 to 8 pCi/L) only — Consider HRV or ERV ventilation as a less invasive alternative.
A certified mitigation contractor evaluates the foundation during the site visit and recommends the appropriate technique. Most Front Range single-family homes match one of the first three categories, which means SSD or SMD is usually the answer.
How diagnostic testing guides technique selection
Certified mitigation contractors run several diagnostic tests during the initial site visit to confirm which technique will work best. A communication test (sometimes called a sub-slab pressure field extension test) drills small holes into the slab at several locations and measures pressure response when a vacuum source is applied. Good pressure communication across the slab indicates SSD will work efficiently from a single suction point. Poor communication suggests multiple suction points or a different technique entirely.
Visual inspection of foundation walls, sump pits, floor drains, and visible cracks identifies entry pathways that may need sealing alongside the primary mitigation. Inspection of the slab gravel layer through the test holes confirms whether the modern code-standard 4-inch gravel layer is present or whether the home has minimal sub-slab permeability. Older Front Range homes occasionally show minimal or no gravel under the slab, which limits SSD effectiveness from a single suction point and may require multiple points or a supplemental technique.
Why certified contractors matter
Radon mitigation technique selection requires expertise that a general handyman or remodeling contractor typically does not have. CDPHE-certified mitigation contractors hold credentials through the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB) and have completed specific training on diagnostic testing, system design, installation practices under ASD-1995, and post-installation verification. State radon programs maintain public rosters of certified contractors, and EPA recommends working only with credentialed professionals.
Uncertified installations sometimes appear in Front Range homes at lower cost but often fail to achieve the expected radon reduction. Common defects include undersized fans for the home’s actual sub-slab permeability, exhaust terminations that violate setback requirements from windows and doors, missing manometers, unsealed sumps or floor drains that short-circuit the system, and failure to verify reduction with post-installation testing. Repairing or replacing a defective uncertified system often costs more than the original installation and effectively doubles the homeowner’s total mitigation spend.
References
- EPA consumer’s guide to radon reduction techniques — US Environmental Protection Agency
- CDPHE radon mitigation program and contractor list — Colorado Department of Public Health and Environment
- American Lung Association radon mitigation overview — American Lung Association
- ICC International Residential Code Appendix F radon-resistant construction — International Code Council
Front Range homeowners with a recent elevated radon test can use our contact page to connect with a CDPHE-certified mitigation contractor who can evaluate the right technique for the home’s specific foundation.