How to Reduce Radon in San Antonio Homes

Radon is a colorless, odorless, and tasteless radioactive gas that forms naturally from the decay of uranium in soil, rock, and water. It can seep into homes through cracks in foundations, gaps around pipes, sump pits, and other openings—accumulating to dangerous levels indoors. In San Antonio, where geology includes significant uranium-rich bedrock and porous limestone formations, radon exposure is a serious and often overlooked public health concern. The U.S. Environmental Protection Agency (EPA) estimates that radon is responsible for approximately 21,000 lung cancer deaths annually in the United States, making it the second leading cause of lung cancer after smoking. For San Antonio residents, understanding how to reduce radon in homes is not just a matter of comfort—it’s a critical step toward protecting long-term health.

Unlike other indoor air pollutants, radon cannot be detected by human senses. Without testing, homeowners have no way of knowing whether their living spaces contain unsafe concentrations. The good news is that radon levels can be effectively reduced through proven, scientifically validated methods. This guide provides a comprehensive, step-by-step roadmap tailored to the unique environmental and structural conditions of San Antonio homes. Whether you live in a century-old brick bungalow in King William or a modern suburban build in the Northwest Hills, this tutorial will empower you with actionable knowledge to mitigate radon risk and create a safer indoor environment for your family.

Step-by-Step Guide

Step 1: Test Your Home for Radon

The first and most essential step in reducing radon is testing. You cannot mitigate what you do not measure. The EPA and the Surgeon General recommend that all homes in the United States be tested for radon, regardless of geographic region or home age. In San Antonio, radon levels vary significantly even within the same neighborhood due to differences in soil composition, foundation type, and construction methods.

There are two primary types of radon tests: short-term and long-term. Short-term tests, typically lasting 2 to 7 days, provide a quick snapshot of radon levels and are ideal for initial screening. Long-term tests, which run for 90 days or more, offer a more accurate picture of average annual exposure, accounting for seasonal fluctuations. For San Antonio homeowners, we recommend starting with a short-term test during the winter months when homes are sealed tightly and indoor air pressure differentials are most pronounced—conditions that tend to draw more radon indoors.

Choose a test kit certified by the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). These kits are available at hardware stores, online retailers, or through the Texas Department of State Health Services. Place the test device in the lowest livable level of your home—such as a basement, crawl space, or first-floor bedroom—away from drafts, high humidity, and exterior walls. Follow the manufacturer’s instructions precisely. After the test period, mail the device to the lab for analysis. Results are typically delivered within a week.

If your test result is 4 picocuries per liter (pCi/L) or higher, the EPA recommends taking action to reduce radon. Even levels between 2 and 4 pCi/L pose some risk, and mitigation may still be advisable, especially for households with children, elderly residents, or smokers.

Step 2: Identify Entry Points

Once you’ve confirmed elevated radon levels, the next step is identifying how the gas is entering your home. San Antonio’s geology—characterized by the Edwards Aquifer and porous limestone bedrock—means radon can migrate upward through soil and rock with relative ease. Common entry points include:

• Cracks in concrete slabs or foundation walls
• Gaps around service pipes, utility conduits, and cable entries
• Construction joints between walls and floors
• Crawl space openings or uncovered dirt floors
• Water from private wells (less common but still possible)
• Porosity in block walls or mortar joints

To locate these entry points, conduct a visual inspection of your home’s foundation. Look for visible cracks, especially near the floor-wall junction. Use a flashlight to examine the underside of floor joists in crawl spaces. Pay special attention to areas where pipes or wiring penetrate the foundation. In homes with sump pumps, check the seal around the pump and lid. Older homes built before the 1980s are more likely to have unsealed foundations and are at higher risk.

For a more thorough assessment, consider hiring a certified radon measurement professional who can use specialized tools such as smoke pencils or tracer gas detectors to visualize airflow patterns and pinpoint radon entry zones. These professionals are trained to identify subtle pressure differentials that drive radon infiltration—a critical factor in San Antonio’s unique climate, where temperature and humidity shifts can alter indoor-outdoor air pressure daily.

Step 3: Seal Foundation Cracks and Openings

Sealing is a foundational (literally) step in radon mitigation. While sealing alone is rarely sufficient to reduce radon to safe levels, it is a necessary complement to active mitigation systems. In San Antonio’s climate, where seasonal rains and temperature swings cause concrete to expand and contract, cracks are common and tend to reopen over time. Therefore, sealing must be done with durable, flexible materials.

Use a high-quality, polyurethane-based caulk designed for concrete and masonry. Avoid silicone or latex caulks, which degrade quickly under soil pressure and moisture exposure. Apply sealant to all visible cracks in floors and walls, paying particular attention to joints where the foundation meets the slab. For larger gaps, use expanding foam sealant specifically rated for radon and soil gas applications. Do not overfill—foam should be applied in thin layers and allowed to cure fully before resealing.

Also seal around all penetrations: plumbing stacks, electrical conduits, gas lines, and sump pump openings. Use rubber gaskets or compression fittings where possible. For crawl spaces, cover exposed soil with a minimum 6-mil polyethylene vapor barrier, overlapping seams by at least 12 inches and sealing edges with tape designed for radon mitigation. This barrier prevents radon from rising directly from the soil into the living space.

Remember: sealing is not a standalone solution. It reduces the flow of radon but does not eliminate the source. Combining sealing with active soil depressurization yields the most effective results.

Step 4: Install an Active Soil Depressurization (ASD) System

Active Soil Depressurization (ASD) is the most effective and widely used method for reducing radon in homes. It works by creating a negative pressure field beneath the foundation, drawing radon gas from the soil before it can enter the home and venting it safely above the roofline. ASD systems are proven to reduce radon levels by 80% to 99% when properly installed.

In San Antonio, where homes are often built on slab-on-grade foundations rather than basements, the most common ASD system is called a “sub-slab depressurization” system. Here’s how it works:

1. A 3- to 4-inch PVC pipe is inserted vertically through the concrete slab into the soil or gravel layer beneath.
2. The pipe is connected to a specially designed, continuously running radon vent fan, typically installed in the attic, garage, or outside the home.
3. The fan pulls radon-laden air from beneath the slab and exhausts it above the roofline, where it quickly dilutes in the outdoor air.
4. The system includes a U-tube manometer (pressure gauge) to monitor airflow and ensure the fan is operating correctly.

Installation should be performed by a certified radon mitigation professional licensed by the NRPP or NRSB. DIY installations are strongly discouraged due to the complexity of system design, the need for precise fan sizing, and the importance of achieving proper negative pressure without creating backdrafting hazards for combustion appliances.

For homes with crawl spaces, a “sub-membrane depressurization” system is used instead. The vapor barrier installed over the soil is sealed at the edges, and one or more suction points are installed beneath it to draw radon out before it enters the living area. This method is particularly effective in San Antonio’s humid climate, where moisture control is also a concern.

After installation, retest your home to verify radon levels have dropped below 2 pCi/L. Most systems require minimal maintenance but should be inspected annually to ensure the fan is running and the piping remains intact.

Step 5: Improve Ventilation and Air Exchange

While ASD systems are the primary defense against radon, increasing overall ventilation can provide supplemental benefits. In San Antonio, where homes are often sealed for energy efficiency, indoor air stagnation can contribute to radon accumulation. Natural ventilation is not always practical due to climate conditions, but mechanical ventilation can help.

Install or upgrade your home’s exhaust fans in bathrooms and kitchens. These fans should vent directly outdoors—not into attics or crawl spaces. Use timers or humidistats to ensure they run long enough to remove stale air after showers or cooking.

Consider installing a Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV). These systems bring in fresh outdoor air while recovering heat (or cooling) from the outgoing air, maintaining energy efficiency while improving indoor air quality. HRVs/ERVs are especially useful in tightly constructed modern homes and can reduce radon concentrations by 25% to 50% when used in conjunction with ASD.

Open windows and doors periodically during mild weather to increase air exchange. While this is not a long-term solution, it can be a helpful temporary measure during testing or while waiting for professional mitigation.

Step 6: Test Again and Monitor Continuously

Radon mitigation is not a one-time task. Levels can change due to seasonal variations, foundation settling, landscaping changes, or modifications to your home’s HVAC system. After installing any mitigation system, retest your home within 24 to 48 hours to confirm effectiveness. Then, conduct a follow-up test after 3 months to ensure long-term stability.

For ongoing peace of mind, consider installing a continuous radon monitor (CRM). These electronic devices provide real-time readings and can alert you to sudden spikes in radon levels. Many models connect to smartphone apps and log historical data, making it easy to track trends. CRMs are especially valuable in homes with well water or those located near newly constructed buildings or roadways that may alter subsurface gas flow.

Retest every two years, even if your system appears to be working. Changes in groundwater levels, nearby construction, or even new landscaping can affect radon migration patterns. In San Antonio, where urban development is rapid and aquifer levels fluctuate, regular monitoring is a prudent investment in health.

Best Practices

Use Certified Professionals

Radon mitigation is not a typical home repair. It requires specialized knowledge of soil science, building dynamics, and ventilation engineering. Always hire a contractor certified by the NRPP or NRSB. These professionals undergo rigorous training, pass competency exams, and are required to follow EPA-recommended protocols. In Texas, while certification is not legally mandated, choosing a certified provider ensures you receive a system designed to meet national standards.

Ask for references, proof of certification, and a written warranty on the installed system. Reputable contractors will provide a pre-mitigation test report, a detailed proposal, and a post-mitigation verification test. Avoid contractors who offer “quick fixes” or guarantee 100% radon elimination—no system can guarantee zero radon, but all certified systems can reduce levels to safe thresholds.

Design for New Construction

If you’re building a new home in San Antonio, radon-resistant construction techniques are far more cost-effective than retrofitting later. The EPA recommends incorporating the following features during construction:

• A 4-inch layer of clean, coarse gravel beneath the slab
• A vapor barrier (6-mil polyethylene) over the gravel
• A 3- to 4-inch PVC pipe stubbed vertically through the slab and capped (radon rough-in)
• Sealed foundation penetrations and joints
• Properly sealed and insulated crawlspace walls

These features allow for easy installation of an active mitigation system later if testing reveals elevated levels. Many San Antonio builders now offer radon-resistant construction as an upgrade option. Ask your builder to include it—it adds only $300 to $500 to the cost of a new home but can save thousands in future mitigation expenses.

Manage Water Sources

While soil is the primary source of radon in most homes, private wells can also contribute, especially in rural areas of San Antonio where groundwater is drawn from the Edwards Aquifer. Radon dissolves in groundwater and is released into the air when water is used for showering, washing, or cooking.

If your home uses a private well and your radon levels remain elevated after soil mitigation, test your water. The EPA recommends testing well water if indoor air radon exceeds 4 pCi/L and you suspect water as a contributor. If levels are high, install an aeration system or granular activated carbon (GAC) filter at the point of entry. Aeration systems are more effective for high radon concentrations, while GAC filters are suitable for moderate levels.

Coordinate with HVAC Systems

Improperly balanced HVAC systems can inadvertently increase radon infiltration. When exhaust fans or furnaces create negative pressure in the home, they can draw more radon from the soil. Ensure your HVAC system is properly sized and balanced. Have a professional inspect your ductwork for leaks and ensure return air ducts are not pulling air from crawl spaces or basements.

Consider installing a dedicated outdoor air intake for your HVAC system. This provides controlled ventilation without relying on unsealed foundation cracks to supply makeup air.

Document Everything

Keep a permanent record of all radon tests, mitigation installations, and maintenance activities. Store this documentation in a fireproof location and share it with future homeowners. In Texas, disclosure laws require sellers to inform buyers of known radon hazards. Having a documented history of testing and mitigation not only protects your family’s health but also increases your home’s market value and transparency.

Tools and Resources

Recommended Testing Kits

• ProLab 5000 Radon Test Kit – Short-term charcoal canister test, NRPP-certified, widely used by professionals.
• Airthings Corentium Home – Digital continuous monitor with real-time readings and app connectivity.
• SafeHome Radon Test Kit – Long-term alpha track detector, ideal for seasonal variation analysis.

Professional Mitigation Equipment

• RadonAway RP145 Fan – Quiet, energy-efficient fan designed for sub-slab depressurization.
• Radon Mitigation Pipe Kit (3” or 4” PVC) – Includes fittings, couplings, and flashing for roof penetrations.
• Manometer Tube – Measures pressure differential to confirm system performance.
• 6-Mil Polyethylene Vapor Barrier – For crawl space encapsulation and sub-membrane systems.

Local and National Resources

• Texas Department of State Health Services (DSHS) Radon Program – Offers free radon test kits to Texas residents, educational materials, and a directory of certified professionals. Visit dshs.texas.gov/radon.
• EPA Radon Website – Comprehensive guides, maps, and scientific data. Visit epa.gov/radon.
• National Radon Proficiency Program (NRPP) – Search for certified mitigators in San Antonio: nrpp.info.
• San Antonio Bexar County Health District – Hosts community radon awareness events and provides localized data on regional soil radon potential.

Software and Apps

• Airthings View – Monitors radon, CO2, humidity, and temperature via smartphone.
• Radon Watch – Tracks historical data and alerts users to trends or spikes.
• Radon Map (EPA) – Interactive map showing radon potential by ZIP code in Texas.

Real Examples

Example 1: Historic Home in King William

A 1920s brick home in the King William Historic District had radon levels of 12.3 pCi/L after a short-term test. The home had a full basement with exposed block walls and a dirt floor. The mitigation team installed a sub-membrane depressurization system, sealing the entire basement floor with a 10-mil polyethylene barrier and sealing all wall-floor joints. Two suction points were installed beneath the barrier, connected to a 24/7 fan vented through the roof. Post-mitigation testing showed levels dropped to 0.8 pCi/L. The homeowner also installed a continuous monitor, which now alerts them to any fluctuations. The system has required no maintenance in five years.

Example 2: New Construction in the Northwest Hills

A family built a new home in the Northwest Hills with radon-resistant features included during construction: gravel layer, vapor barrier, and a roughed-in PVC pipe. After occupancy, a long-term test showed levels at 3.2 pCi/L—below the EPA action level but still elevated. The homeowner decided to activate the pre-installed system by adding a fan. Within a week, levels dropped to 0.9 pCi/L. The cost of adding the fan was under $600—far less than retrofitting a system later would have cost.

Example 3: Apartment Complex in East San Antonio

An apartment complex with slab-on-grade units had multiple tenants report respiratory issues. Testing revealed elevated radon in several units, ranging from 5.1 to 8.7 pCi/L. The property manager hired a certified mitigator who installed individual sub-slab depressurization systems in each affected unit. Each system was connected to a central monitoring dashboard. Within two months, all units tested below 2 pCi/L. The complex now requires radon testing before each new lease and includes mitigation system maintenance in the property’s annual budget.

Example 4: Home with Private Well

A rural home on the outskirts of San Antonio had radon levels of 6.5 pCi/L in the air. After installing an ASD system, levels dropped to 2.1 pCi/L—but still above the recommended threshold. Water testing revealed radon concentrations of 20,000 pCi/L in the well. A point-of-entry aeration system was installed, reducing waterborne radon to less than 500 pCi/L. Air levels subsequently fell to 0.7 pCi/L. This case illustrates the importance of testing both air and water in homes with private wells.

FAQs

Is radon a problem in San Antonio?

Yes. While San Antonio is not classified as a high-radon zone like parts of Iowa or Pennsylvania, the city sits atop uranium-rich limestone and shale formations of the Edwards Aquifer. Radon levels vary widely by neighborhood, and many homes have been found with dangerous concentrations. The EPA estimates that nearly 1 in 15 homes nationwide has elevated radon, and San Antonio is no exception.

Can I test for radon myself?

Yes. DIY test kits are reliable and affordable. Choose an NRPP- or NRSB-certified kit and follow instructions precisely. For peace of mind, especially if you’re buying or selling a home, consider hiring a professional for verification.

How much does radon mitigation cost in San Antonio?

Typical costs range from $800 to $2,500, depending on home size, foundation type, and system complexity. Sub-slab depressurization systems average $1,200 to $1,800. Costs are generally lower in new construction if radon-resistant features are installed upfront.

How long does radon mitigation last?

A properly installed ASD system can last 20 years or more. The fan typically lasts 5 to 10 years and may need replacement. Regular testing and annual inspections ensure continued effectiveness.

Does sealing cracks alone fix radon?

No. Sealing reduces radon entry but does not eliminate the pressure differential that draws gas into the home. Sealing must be combined with active soil depressurization for reliable, long-term reduction.

Can radon affect my pets?

Yes. Pets, especially dogs and cats that spend most of their time indoors, are exposed to the same radon levels as humans. Long-term exposure increases their risk of respiratory illness and lung cancer. Protecting your home protects your entire household.

Are new homes in San Antonio built to prevent radon?

Not automatically. While radon-resistant construction is recommended, it is not required by Texas building codes. Always ask your builder if radon-resistant features are included. If not, request them as an upgrade.

Can I reduce radon without a fan?

Passive methods like increased ventilation, sealing, and crawl space encapsulation can help, but they are rarely sufficient to reduce levels below the EPA action level of 4 pCi/L. Active systems with fans are the only proven method for significant, reliable reduction.

What should I do if I’m buying a home in San Antonio?

Always include a radon test as part of your home inspection contingency. If levels are high, negotiate with the seller to install a mitigation system before closing. Many sellers are willing to cover the cost, as it increases the home’s appeal and marketability.

Conclusion

Reducing radon in San Antonio homes is not just a technical task—it’s a vital act of health protection. The silent, invisible threat of radon gas can linger undetected for years, silently increasing the risk of lung cancer for everyone who breathes the air inside. But with the right knowledge, tools, and professional guidance, every San Antonio home can be made safe.

This guide has walked you through the complete process: from testing and identifying entry points, to sealing, installing active mitigation systems, improving ventilation, and monitoring for long-term safety. We’ve highlighted best practices, recommended tools, and shared real-world examples from across the city to demonstrate what’s possible.

Radon mitigation is not a luxury. It is a necessity. Whether you live in a century-old home with a dirt crawl space or a modern, energy-efficient house on the city’s outskirts, the principles remain the same: test early, act decisively, and maintain vigilance. The investment of time and resources now will pay dividends in health, peace of mind, and property value for years to come.

Take the first step today. Order a test kit. Inspect your foundation. Talk to your builder. Contact a certified professional. Your family’s lungs depend on it.