Sub-slab depressurization in Atlanta: how it works and what to expect

Sub-slab depressurization is the most effective method for reducing radon gas in homes built on a concrete slab. A technician drills one or more suction points through the slab, inserts PVC vent pipe, and connects an inline radon fan that pulls radon-laden soil gas out from under the foundation and exhausts it safely above the roofline. Most installations take four to six hours, and radon levels typically drop well below the EPA action level of 4.0 pCi/L.  

What is sub-slab depressurization and how does it work?

Sub-slab depressurization, often called active sub-slab depressurization or ASD, creates a zone of lower air pressure directly beneath your concrete slab. Because radon moves from high-pressure areas to low-pressure areas, pulling a slight vacuum under the slab intercepts the gas before it seeps through cracks, joints, or utility penetrations into your living space. The system has three main parts:

• Suction pit: A small hole drilled through the slab, sometimes into gravel or loose fill beneath it, that acts as the entry point for soil gas collection.
• PVC vent pipe: Rigid pipe that carries radon from below the slab up through the home or along an exterior wall and out above the roofline.
• Radon fan: An inline fan mounted in the pipe run, typically in the attic or on the exterior. This is the only moving part in the system and runs continuously on a small amount of electricity.

A manometer or U-tube pressure gauge is installed in the pipe so you can see at a glance that the system is pulling negative pressure. If the fluid levels are even, something has changed and it is time to call.  

Do slab-on-grade homes in Atlanta actually have radon problems?

Yes. There is a common assumption that only homes with basements have radon problems. Slab-on-grade homes in the Atlanta metro can test well above the EPA action level of 4.0 pCi/L, and some exceed the WHO reference level of 2.7 pCi/L. The geology underneath much of North Georgia is a significant factor. Granite and gneiss bedrock, which runs through Fulton, Cobb, DeKalb, Forsyth, and Cherokee counties, naturally produces radon as uranium in the rock decays. The Georgia EPA zone designations reflect this risk, and several counties in our service area fall into EPA Radon Zone 1 and Zone 2 classifications, meaning elevated radon potential is built into the ground itself. A concrete slab is not a sealed barrier. Expansion joints, control joints, pipe penetrations, and hairline cracks are all pathways radon uses to enter. Stack effect pressure inside the home, especially in winter when warm air rises and pulls cooler outside air in through the foundation, actively draws soil gas upward. The result is that a slab home can accumulate radon just as a basement home does. If you have not had your home tested, residential radon testing in Atlanta is the right starting point before any mitigation work begins.  

What is sub-membrane depressurization, and is it the same thing?

Sub-membrane depressurization, or SMD, applies the same pressure-reversal principle as ASD but is designed for crawl spaces instead of poured slabs. Rather than drilling through concrete, a technician lays a heavy-duty vapor barrier across the crawl space floor and seals it against the foundation walls. Suction pipes are inserted beneath the membrane, and the radon fan exhausts trapped soil gas to the outside. The two methods are distinct because the foundation type is different, but they often come up together when a home has mixed foundation types: part slab and part crawl space. We perform both. If your home has a crawl space section, ask about sub-membrane depressurization as part of the same assessment. For slab foundations specifically, active sub-slab depressurization is the standard method recommended under ANSI/AARST radon mitigation standards.  

How we install a sub-slab depressurization system: the actual process

Before any drilling starts, we do a diagnostic assessment of the slab. This includes checking what material sits beneath the concrete, loose gravel allows the suction field to spread widely while solid clay restricts it, and identifying existing penetrations like a sump pit that can sometimes serve as the suction point without additional drilling. The installation sequence runs like this:

1. Locate and drill the suction point. We core through the slab, typically a 4-inch diameter hole, and remove enough material beneath to create a suction pit with good communication across the sub-slab area.
2. Test suction field communication. We temporarily cap the hole and use a vacuum gauge to verify that negative pressure is drawing from a wide enough area. If the sub-slab material is too dense, a second suction point may be needed.
3. Run PVC vent pipe. The pipe is routed from the suction pit upward, either through interior closets or along an exterior wall, to a point above the roofline. All penetrations through conditioned space are sealed.
4. Install the radon fan. The fan is placed in an unconditioned location, typically the attic or outside, so that if the fan housing ever develops a leak it does not exhaust radon into living space.
5. Install the manometer. A small pressure gauge is mounted on the pipe in a visible location so you can confirm the system is operating.
6. Seal the slab. The suction pit and any other identified cracks or penetrations are sealed with appropriate caulk or sealant.

Most single-suction-point installations are complete in four to six hours. Homes with dense sub-slab material or multiple foundation sections may take longer.  

What does a finished system look like, and will it disrupt your home?

The pipe run is the most visible part. If routed inside, it typically exits through a closet and is not visible in main living areas. Exterior routing is also common and results in a white PVC pipe running up the side of the house, similar in appearance to a dryer vent stack. The fan produces a low hum, roughly comparable to a bathroom exhaust fan running in another room. Most homeowners stop noticing it within a few days. It runs continuously on low power consumption. You do not need to leave the house during installation. Dust from the core drill is minimal and contained. Normal household activity can continue.  

How do you know the system is working after installation?

The manometer gives you a quick visual check every time you pass it. If the fluid is displaced toward the house side of the gauge, suction is present and the fan is working. That is your daily confirmation. The definitive check is a post-mitigation verification test. ANSI/AARST standards call for this test within 30 days of installation. We use a continuous radon monitor or a short-term charcoal canister placed under closed-house conditions to measure actual radon levels after the system has had time to draw down the soil gas beneath the slab. The result tells you the system is performing as designed and gives you a documented baseline for future reference. For homeowners who want ongoing data, a long-term alpha track detector placed in the home over 90 days or more provides a seasonal average, which is more representative than a single short-term reading. If you want to establish your pre-mitigation radon level before scheduling installation, certified radon testing in Atlanta provides the documented results you need. A radon level assessment can also clarify whether your specific readings require immediate action or continued monitoring. Sub-slab depressurization is one part of a broader set of environmental health services in Atlanta we perform across Cobb, Fulton, DeKalb, Forsyth, Pickens, and surrounding counties.  

FAQs about sub-slab depressurization in Atlanta

 

How long does a sub-slab depressurization system last?

The PVC pipe has an indefinite service life under normal conditions. The radon fan is the component that eventually needs attention. Fan life varies by model and operating conditions, but replacement is straightforward and significantly less expensive than a new installation.  

Can a sump pit be used as the suction point?

Yes. If your slab home has a sump pit, it often provides excellent sub-slab access and can be covered and connected to the vent pipe, avoiding the need to core through the slab. We assess this during the diagnostic phase.  

Will sub-slab depressurization increase my energy bill?

The radon fan draws a small amount of electricity, comparable to a low-wattage light bulb running continuously. It will appear on your bill, but the cost is minor.  

Does the system need maintenance?

Check the manometer periodically. Have the fan inspected if you notice the gauge reading has changed or the hum has shifted. Beyond that, the system requires very little attention. A post-mitigation test at the time of installation and a periodic long-term test every two years are the main monitoring steps.  

Does Georgia require radon disclosure when selling a home?

The Georgia Seller’s Property Disclosure Act, O.C.G.A. 44-1-16, requires sellers to disclose known material defects. Elevated radon levels and the presence or absence of a mitigation system are material facts buyers routinely ask about. A documented, working ASD system is a selling point.  

Do I need a certified technician, or can I install this myself?

DIY radon fan kits exist, but proper diagnostic work, suction field testing, fan sizing, pipe routing to code, and post-mitigation verification require training and calibrated equipment. Technicians certified through NRPP or NRSB have demonstrated competency in the ANSI/AARST standards that govern installation. An improperly installed system can underperform without any visible sign that it is doing so.