Service
Slab Foundation Radon Mitigation in San Diego County
Sub-slab depressurization for the slab-on-grade homes that dominate San Diego construction.
Slab-on-grade is the defining foundation type of postwar Southern California housing, and it is where most local radon mitigation work happens. The concrete is only a few inches thick, and it is penetrated by plumbing, poured against footings, and cut with control joints, each of which is a potential entry route.
Concrete is also not airtight. It is porous, and it shrinks as it cures, opening hairline paths across the entire floor area. This is why sealing alone never solves a radon problem on a slab. It reduces the obvious openings while leaving the diffuse ones untouched.
Sub-slab depressurization solves the problem by making the space under the slab lower in pressure than the room above it. Once that relationship is established, air flows down through cracks instead of gas flowing up.
Why this work matters
- Slab homes place living space in direct contact with soil across the entire footprint.
- Bedrooms on slab mean the highest-exposure hours occur in the highest-contact rooms.
- Control joints and plumbing penetrations concentrate entry at predictable, treatable locations.
- Because the slab is thin, small pressure differences move meaningful volumes of gas.
Signs this service applies to your building
- Confirmed elevated readings in a single-story slab home.
- Visible cracks radiating from corners or along control joints.
- Gaps around plumbing penetrations at toilets, tubs, or utility connections.
- An expansion joint at the perimeter that was never sealed.
- A garage slab poured separately and connected through a shared wall.
- A patio or room addition slab poured against the original foundation.
How the process works
- 1
Locate slab reinforcement
Post-tension cables and rebar are located before any coring. This is critical in San Diego, where post-tension slabs are common in homes built from the late 1970s onward.
- 2
Communication testing
A test hole plus vacuum and remote pressure measurement reveal how far the pressure field extends through the sub-slab material.
- 3
Suction point selection
Placement targets the area with the best communication, generally near the center of the largest continuous slab section and away from perimeter footings.
- 4
Excavate the pit
Material is removed under the core to create a void that lets the fan draw from a wide area rather than choking at the pipe mouth.
- 5
Seal the accessible openings
Control joints, visible cracks, perimeter expansion joints, and plumbing penetrations are sealed with flexible polyurethane.
- 6
Verify pressure field extension
Test holes at the slab perimeter and in distant rooms confirm the vacuum reaches the full footprint before the job is considered complete.
Equipment and materials involved
Post-tension cable locator
Prevents cutting a tensioned cable, which is both a structural and safety hazard.
Core drill with dust extraction
Cuts a clean opening while controlling silica dust inside an occupied home.
Micromanometer with test probes
Quantifies pressure field extension at points across the slab.
Flexible polyurethane sealant
Seals joints and cracks while accommodating normal concrete movement.
Sub-slab suction riser
Sealed at the slab so the fan pulls from the soil rather than the room.
What you get out of it
- Effective reduction in the foundation type most common across San Diego County.
- Minimal visual impact, with the riser typically emerging in a garage or closet.
- Reduced soil moisture migration through the slab.
- Documented pressure field extension, so performance is proven rather than assumed.
- A single fan usually serves the whole home when communication is good.
San Diego County considerations
Tract housing built across Clairemont, Mira Mesa, Santee, and Rancho Peñasquitos is overwhelmingly slab-on-grade, making sub-slab depressurization the default local approach.
Sub-slab fill varies significantly by era and builder. Homes built over clean gravel communicate beautifully with one suction point, while those poured directly on native clay or decomposed granite may need two or three.
Decomposed granite soils common inland can be surprisingly permeable, which sometimes means excellent pressure field extension and sometimes means high airflow that demands a larger fan.
Expansive clay found in parts of the county causes slab cracking over time, which both increases entry pathways and makes flexible sealant selection important.
Frequently asked questions
Can you core a post-tension slab safely?+
Yes, with proper locating. Post-tension cables are under enormous tension and cutting one is a serious structural and safety event. The correct procedure uses scanning equipment to map cable and rebar positions, marks a clear zone, and cores within it. If no safe zone exists at the ideal suction location, the point is relocated or an exterior suction approach is used instead. Coring blind on a post-tension slab is never acceptable.
Is sealing the cracks enough on its own?+
No. Sealing is a supporting measure, never the primary one. Concrete is porous and develops hairline shrinkage cracks across the whole floor area, so gas continues to diffuse through paths too small to see or seal. Sealing does improve system performance by preventing the fan from pulling conditioned indoor air, which lets the vacuum reach further under the slab. It is worth doing, as part of a system.
Where will the pipe come up inside my house?+
Wherever diagnostics show the best communication and the routing is least intrusive, which most often means a garage, a utility closet, a laundry area, or the back of a bedroom closet. From there the pipe runs up into the attic and out through the roof. In some layouts an exterior suction point on the outside of the foundation avoids interior pipe entirely, though it usually communicates less effectively.
What if my home has multiple slab sections?+
Additions, converted patios, and attached garages are typically poured separately, and footings between them block sub-slab airflow. Communication testing will show a vacuum that stops at the boundary. The remedy is a second suction point in the isolated section, tied into the same pipe and fan when capacity allows, so the whole footprint is covered rather than just the original house.
Will the concrete floor be damaged?+
No. A four to five inch core hole in a properly located spot has no meaningful effect on slab performance, and the riser is sealed into it permanently. Sealing existing cracks is cosmetic-neutral to slightly improved. The visible result inside is a pipe emerging from a neat sealed collar, usually in a space where it goes unnoticed.
Related reading
Related services
Available throughout the county
- Slab Foundation Mitigation in San Diego
- Slab Foundation Mitigation in La Jolla
- Slab Foundation Mitigation in Del Mar
- Slab Foundation Mitigation in Carlsbad
- Slab Foundation Mitigation in Encinitas
- Slab Foundation Mitigation in Poway
- Slab Foundation Mitigation in Escondido
- Slab Foundation Mitigation in Chula Vista
- Slab Foundation Mitigation in El Cajon
- Slab Foundation Mitigation in La Mesa
- Slab Foundation Mitigation in Santee
- Slab Foundation Mitigation in National City
- Slab Foundation Mitigation in Coronado
- Slab Foundation Mitigation in Imperial Beach
- Slab Foundation Mitigation in Pacific Beach
- Slab Foundation Mitigation in Mission Valley
- Slab Foundation Mitigation in Clairemont
- Slab Foundation Mitigation in Mira Mesa
- Slab Foundation Mitigation in Rancho Bernardo
- Slab Foundation Mitigation in Rancho Peñasquitos
- Slab Foundation Mitigation in Carmel Valley
- Slab Foundation Mitigation in University City
- Slab Foundation Mitigation in Point Loma
- Slab Foundation Mitigation in Hillcrest
- Slab Foundation Mitigation in North Park
- Slab Foundation Mitigation in South Park
- Slab Foundation 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.