Radon Barrier and Sub-Slab Venting: DIY-Friendly Options Under a New Slab

Radon is a colorless, odorless gas that can accumulate beneath a newly poured slab. It travels through soil and enters spaces where ventilation is limited, and exposure can accumulate over time. Understanding its behavior helps you plan for a safer, longer-lasting building envelope.

Health implications are primarily linked to lung cancer risk, with certain populations being more affected. Rather than alarm, focus on realistic mitigation strategies and routine testing as part of your build. Local guidelines and testing recommendations vary, so check with the appropriate authority and refer to official product data sheets or manufacturer instructions for specifics.

Health effects and exposure pathways

Radon is a colorless, odorless gas that seeps up from the soil into your home. It’s formed by the natural breakdown of uranium in rocks and soil. Under a new slab, it can accumulate because concrete is porous.

Exposure to radon over time increases lung cancer risk. This isn’t just about smokers; non-smokers are also at risk. The more you’re exposed, the higher your chances of developing lung cancer.

Radon enters homes through cracks in foundations, gaps around service pipes, and even through porous concrete slabs. It’s often unseen, making it crucial to test for it.

Testing basics and action levels

Radon testing is straightforward but needs time. There are two main types: short-term (2-7 days) and long-term (90 days or more). Short-term tests give a quick snapshot, while long-term tests provide a better average.

The EPA recommends fixing your home if the radon level is 4 picocuries per liter (pCi/L) or higher. This is not a ‘safe’ level; it’s just an action level. Some states have lower recommended levels.

Before building, test for radon in the soil where you’ll pour your slab. After construction, do another test to get a post-construction baseline. Always follow local guidelines and testing recommendations.

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Active systems use sub-slab depressurization with a fan to draw gas away from living spaces, while passive measures rely on barriers, seals, and natural venting. Each approach has distinct configurations and practical implications under a new slab. Consider how your site conditions and future plans shape the choice.

Passive measures typically require careful sealing and barrier placement, with lower ongoing energy use but potentially less certainty in high-risk scenarios. Active systems offer stronger control but add equipment, maintenance, and energy considerations. Use vetted guidelines and local rules to determine the best fit for your project and region.

Active sub-slab depressurization (SSD)

Active SSD systems work by creating a vacuum under your new slab to prevent radon gas from entering your home. Here’s how:

The system consists of a fan, piping, and a collection point called a sump. The fan sucks air out of the sump, drawing radon-laden soil gas with it. This gas is then vented outside, away from living spaces.

SSD is recommended when you have high indoor radon potential, porous sub-slab concrete pours, or existing high readings. It’s more reliable but also more complex and costly to install than passive systems.

Operational impacts: SSD uses electricity, so there’s a small energy cost. Proper installation minimizes backdraft risk, drawing air in instead of pushing radon out.

Passive barriers and ventilation

Passive systems rely on natural pressure differences to keep radon out. They’re simpler and cheaper but less reliable than active systems.

Membrane barriers: These are plastic sheets laid under your slab, sealing off the path for radon gas. They work best when the seal is tight and the slab is new.

Perimeter vents: These are small pipes around the perimeter of your foundation that allow soil gas to escape naturally. They’re useful in areas with low radon potential or when you can’t use a barrier.

Natural ventilation: This relies on air moving through your home’s cracks and gaps, diluting indoor radon levels. It’s not recommended as a primary mitigation strategy due to its unpredictability.

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Set clear goals for barrier integrity and compatibility with your slab design and insulation. Define how the barrier will be installed, how seams will be treated, and what inspections you must pass before pouring. Keep the plan aligned with local permits and code expectations as you scope the work.

Material selection hinges on barrier type, seam methods, and how you will anchor to rebar or integrate with future systems. Prepare for site prep like moisture control and drainage coordination, and map out how trades will coordinate to protect the barrier during construction.

Design considerations and code/permit checks

The first step in planning your DIY radon barrier is understanding what your local building codes require. You’ll need to verify clearances, ensure compatibility with other systems like insulation or radiant floor heating, and consult with inspectors or engineers if needed.

Check for required membrane thickness, seam overlap rules, and any specific installation guidelines. Radon barriers should be continuous and cover the entire slab area to be effective. Ensure you understand how to handle penetrations like plumbing pipes or electrical conduit.

Confirm that your design allows for proper venting. This might involve trenching or creating channels for future vent pathways. Always consult with local authorities having jurisdiction (AHJs) to ensure compliance.

Follow an installation sequence that ensures full-area coverage, correct orientation, and seam integrity with compatible tape or sealants. Treat every seam as critical, and verify overlap and continuous coverage before moving on. Penetrations must be sealed with approved products to keep leaks from forming around conduits or pipes.

Protect the membrane during the pour by keeping it clean and unpunctured, using protective boards as needed, and avoiding traffic that could damage it. Inspectors will look for clean seams, sealed penetrations, and proper protection, so keep visual records and a simple checklist handy.

Seaming, taping, and penetration details

Proper seam overlap and sealing are crucial for an effective radon barrier. Use approved tapes or mastics to maintain integrity.

Seam Overlap: Overlapping seams by at least 6 inches creates a continuous barrier that prevents radon gas from migrating through gaps. Ensure the overlap is even and consistent across the entire sub-slab area.

Taping/Sealing: Use butyl tape or concrete-friendly tape/mastic to seal seams. Apply the tape along the entire width of the overlap, pressing firmly to ensure a tight seal. Some tapes may require priming before application; follow manufacturer’s instructions.

Penetration Seals: Seal around pipes, conduits, and sump lines using approved gaskets or sealants. Maintain clearances as per manufacturer’s instructions to prevent leaks or punctures at penetrations. Ensure all seals are tight and free from gaps or cracks.

Protecting the barrier during and after the pour

Temporary protection of the radon membrane is essential to prevent damage during concrete placement. Follow these guidelines for effective protection.

Before Pour: Cover the membrane with geotextile fabric or rigid boards to protect it from concrete spillage, tools, and foot traffic. Ensure the protective layer extends beyond the edges of the membrane to provide full coverage.

During Pour: Keep the membrane clean and free from punctures by preventing direct contact with concrete. Place reinforcement as needed, ensuring it does not rest directly on the membrane. Monitor the pour process to ensure no damage occurs.

After Pour: Once the concrete has cured, perform a visual inspection of the membrane to ensure no punctures or damage have occurred during the pouring process. If any damage is found, repair immediately to maintain the integrity of the radon barrier.

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Decide between a passive venting approach and a plan that allows future conversion to a fan-powered system. Consider climate, soil conditions, and how you want to handle future maintenance and potential upgrades. This choice influences how you route vents and plan exterior terminations during the build.

Describe how to route vent stacks during pour, including pipe sizing, vertical runs, and exterior terminations. For future activation, outline fittings and rough wiring needs, then detail practical steps for installing under/through the slab without creating cold bridges or leaks.

Passive stack placement and sizing

When routing passive vent stacks, consider these principles:

Typical Routing: Run pipes from the slab’s center to avoid creating pressure gradients. Keep them 10 feet apart.

Avoid Re-entry Points: Ensure stacks don’t re-enter the house to prevent backdrafts. Seal any gaps with caulk or foam.

Freezing Concerns: Use 4-inch Schedule 40 PVC pipe for durability and size it to handle expected airflow. Insulate exterior runs in cold climates.

Upgrading to an active fan later

Design your passive system with future fan installation in mind:

Accessible Location: Place the fan near the slab’s center, accessible from outside. This lets you install a fan without digging up the slab.

Conduit and Mounting: Run 1/2-inch conduit from the fan location to your main electrical panel. Include a junction box for easy fan installation later.

Fan Selection: Consult with professionals before choosing a fan. They’ll help you pick one sized right for your slab’s volume and air changes per hour (ACH) needs.

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Identify all joints and penetrations, then plan the sealing sequence and prioritize likely leak paths. Establish a logical order that minimizes future fixes and keeps work within a realistic DIY scope. Document key joints for reference and inspection.

Explore material options that tolerate moisture and temperature changes, such as polyurethane or silicone, and note compatibility with other slab materials. Include surface preparation steps, curing guidance, and a maintenance plan to keep seals performing over time.

Long-term durability and maintenance of seals

Maintaining your sealants is crucial for long-lasting protection against radon intrusion. Here’s how to keep them in tip-top shape.

Use high-quality, compatible sealants designed for concrete slabs. Silicone or polyurethane caulks are good choices. Re-caulk every 5-7 years, depending on traffic and climate conditions.

Inspect your seals annually. Look for cracks, gaps, or signs of deterioration. Use a flashlight to check hard-to-reach areas. If you find any issues, repair them promptly using the same type of sealant.

If you notice persistent leaks or extensive damage, it’s time to call a professional. They have specialized equipment and expertise to diagnose and fix problems efficiently.

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Outline the three main options—barrier-only, passive venting, and active SSD—in terms of scope and practical feasibility for a DIY project. Tie in how these choices influence labor needs and potential material choices. Use local quotes to refine your plan and budget.

Discuss how effectiveness can vary with soil and climate, and how energy or ventilation needs may shift based on system type. Provide a decision framework and a checklist to verify warranties, code compliance, and installation considerations before committing to a path.

Typical cost components and what affects price

Installing a radon barrier and sub-slab venting involves several material and labor costs. Here’s what you can expect:

The main materials are:
– Radon membrane: $0.50 – $2 per sq ft
– Sealants: $10 – $30 per tube
– Pipes (for venting): $1 – $5 per ft
– Vents and fans: $50 – $300 each

Labor can vary widely depending on your DIY skills and local contractors. Expect to pay:
– Barrier-only: $2 – $6 per sq ft (DIY: $0 – $1)
– Passive venting: $3 – $8 per sq ft (DIY: $1 – $3)
– Active SSD: $5 – $10 per sq ft (DIY: $2 – $5)

Factors affecting price: Membrane quality, site preparation, pipe runs, fan type. Get multiple estimates to compare.

Performance expectations and when to re-test

After installation, it’s crucial to test your system’s effectiveness. Here’s how:

Wait at least 24 hours after the pour before testing. Then, perform a post-construction radon test. Aim for a reduction of at least 50% compared to pre-installation levels.

Ideal results are below 4 pCi/L, but even a 2 pCi/L reduction significantly improves indoor air quality. Retest every two years or after any major changes to your home’s structure.

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Lay out safety foundations, including confined-space awareness, PPE, and how to manage electrical aspects for future venting equipment. Highlight monitoring needs when working under a slab or near energized components. Follow a cautious approach to reduce risk.

Explain common mistakes like gaps in seams, unsealed penetrations, or improper vent terminations, and describe how these impact radon performance. Outline clear red flags that suggest bringing in a licensed professional, and provide quick checklists to assess readiness and permit requirements.

Preventing backdrafting and re-entrainment

Backdrafting occurs when radon gas is pulled back into the house through gaps in your vent termination. Re-entrainment happens when outdoor air gets sucked back into the slab, reducing the effectiveness of your system.

To prevent these issues:

– Ensure your vent pipe extends at least 10 inches above the roof or 2 feet above any opening within 10 feet. This prevents backdrafting.

– Place the termination point away from windows, doors, and other openings to minimize re-entrainment.

Final testing, documentation, and warranty tips

After installation, it’s crucial to test your system’s performance. Keep records for future reference or inspections.

Here’s what you should do:

– Conduct a post-installation radon test to ensure your system is working properly. If the results are above 4 pCi/L, consider upgrading to an active fan.

– Maintain installation records and warranties from suppliers. This is especially important if you plan on selling your home in the future.

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