Service
Crawl Space Radon Mitigation in San Diego County
Sub-membrane depressurization for raised-foundation homes, sealing exposed soil and venting gas before it reaches the floor above.
A crawl space is a room made of dirt with a house on top of it. Whatever the soil emits, whether radon, moisture, or musty organic odor, enters the crawl space first and then migrates upward through floor penetrations, ductwork chases, and the gaps around plumbing.
The standard solution is sub-membrane depressurization. A heavy polyethylene membrane is laid over the entire soil surface, sealed at seams, piers, and the perimeter, and a fan draws from beneath it. The membrane becomes the barrier and the space beneath it becomes the plenum.
Executed well, this approach usually delivers larger reductions than slab work because the membrane covers the entire soil surface rather than relying on a vacuum spreading through gravel.
Why this work matters
- Exposed crawl space soil is a continuous, unrestricted source of soil gas directly beneath living space.
- Air in the crawl space does not stay there. A meaningful fraction of the air in the rooms above originates below the floor.
- The same membrane that stops radon also dramatically reduces ground moisture, which addresses mold, wood decay, and pest attraction.
- Ductwork routed through crawl spaces can draw crawl air directly into the distribution system if joints leak.
Signs this service applies to your building
- Exposed dirt floor with no vapor barrier, or a torn and displaced old barrier.
- Musty odors noticeable at floor level or when the HVAC starts.
- Elevated indoor humidity that resists dehumidification.
- Visible efflorescence, damp soil, or standing water after rain.
- Rusting duct straps, cupping hardwood, or soft subfloor.
- A radon test above 4.0 pCi/L in a raised-foundation home.
How the process works
- 1
Crawl space assessment
Access, headroom, soil condition, standing water, existing barrier, vent locations, ductwork, and combustion appliances are all documented.
- 2
Prepare the ground
Debris and sharp rock are removed and the surface graded so the membrane lies flat and will not be punctured.
- 3
Install the perforated collection network
Where soil is tight, perforated pipe or a permeable mat is laid beneath the membrane so vacuum distributes across the full footprint.
- 4
Lay and seal the membrane
Reinforced polyethylene is installed with overlapped seams, sealed to piers, footings, and perimeter walls, creating a continuous sealed plenum.
- 5
Connect riser and fan
The riser ties into the collection network, exits the crawl space, and terminates above the roofline with the fan outside the conditioned envelope.
- 6
Verify under the membrane
Pressure measurements taken beneath the membrane at several points confirm the vacuum reaches the entire area, followed by a post-mitigation test upstairs.
Equipment and materials involved
Reinforced polyethylene membrane
Typically a heavy, puncture-resistant sheet rated for ground contact rather than thin builder plastic.
Perforated collection pipe or drainage mat
Distributes vacuum evenly beneath the membrane, especially over clay.
Seam tape and butyl sealant
Bonds overlaps and seals the membrane to piers, walls, and penetrations.
Mechanical termination bar
Fastens the membrane to foundation walls so the seal survives movement and time.
Sub-membrane pressure test points
Permit verification that vacuum extends to the far corners.
What you get out of it
- Large radon reductions, often the most dramatic of any foundation type.
- Substantially drier crawl space with reduced mold and wood decay risk.
- Fewer pest and odor problems from encapsulated soil.
- Cleaner, more usable crawl space for future plumbing and electrical work.
- Improved comfort on the floor above from reduced ground moisture and drafts.
San Diego County considerations
Older San Diego neighborhoods, including much of North Park, South Park, Hillcrest, and the older sections of Point Loma and Ocean Beach, are full of pre-1950 raised-foundation homes with open crawl spaces.
Coastal marine air combined with exposed soil creates persistent crawl space humidity that a membrane addresses at the same time as radon.
Many local crawl spaces have low headroom, which makes careful planning of material staging and membrane layout essential to a clean installation.
Hillside lots common in Point Loma and La Jolla produce crawl spaces that are shallow on one side and nearly full height on the other, requiring stepped membrane detailing along the grade.
Frequently asked questions
Is a vapor barrier alone enough to fix radon?+
Rarely. A sealed membrane slows diffusion but does not create the pressure difference that keeps soil gas out. Without a fan drawing beneath it, gas finds seams, edges, and penetrations. A membrane can reduce concentrations somewhat, particularly in a home that started only slightly elevated, but sub-membrane depressurization is what produces reliable, verified reductions.
Should crawl space vents stay open or be closed?+
It depends on the design. In a sub-membrane depressurization system the soil is sealed off, and vents can generally remain as they are because the barrier, not the ventilation, is doing the work. In an unsealed crawl space, heavy ventilation dilutes radon but also imports humid coastal air in summer, which can create a moisture problem while partially addressing a gas problem. Sealing the soil is the better trade.
Can I still use my crawl space for storage?+
Yes, with care. The membrane is durable but not indestructible, so sharp objects and heavy point loads should be placed on protective boards rather than directly on the sheet. Any puncture that occurs later should be patched with seam tape, since an open hole is a direct bypass around the barrier and will reduce system performance.
How does this affect my ductwork?+
Positively, in most cases. Sealing the soil reduces the humidity and particulate load in the crawl space, so any air that leaks into return ducts is cleaner and drier. It is worth having duct joints sealed at the same time, because leaky returns in a crawl space actively pull crawl air into the living space and can undermine both radon and comfort goals.
What about homes with both a crawl space and a slab section?+
That combination is common in homes with additions, and it usually requires treating both areas. Sub-slab suction under the slab section and sub-membrane depressurization under the crawl portion can often be tied into a single riser and fan if the fan has adequate capacity. Diagnostics determine whether one fan can serve both or whether a second system is warranted.
Related reading
Related services
Available throughout the county
- Crawl Space Mitigation in San Diego
- Crawl Space Mitigation in La Jolla
- Crawl Space Mitigation in Del Mar
- Crawl Space Mitigation in Carlsbad
- Crawl Space Mitigation in Encinitas
- Crawl Space Mitigation in Poway
- Crawl Space Mitigation in Escondido
- Crawl Space Mitigation in Chula Vista
- Crawl Space Mitigation in El Cajon
- Crawl Space Mitigation in La Mesa
- Crawl Space Mitigation in Santee
- Crawl Space Mitigation in National City
- Crawl Space Mitigation in Coronado
- Crawl Space Mitigation in Imperial Beach
- Crawl Space Mitigation in Pacific Beach
- Crawl Space Mitigation in Mission Valley
- Crawl Space Mitigation in Clairemont
- Crawl Space Mitigation in Mira Mesa
- Crawl Space Mitigation in Rancho Bernardo
- Crawl Space Mitigation in Rancho Peñasquitos
- Crawl Space Mitigation in Carmel Valley
- Crawl Space Mitigation in University City
- Crawl Space Mitigation in Point Loma
- Crawl Space Mitigation in Hillcrest
- Crawl Space Mitigation in North Park
- Crawl Space Mitigation in South Park
- Crawl Space Mitigation in Ocean Beach
Not sure where to start?
Testing is the first step. Send a note describing your home, its foundation type, and any test results you already have.