Can you fix radon by sealing cracks? What DIY steps help, and what doesn't

When a radon test comes back high, many homeowners' first instinct is to grab a tube of caulk and seal every crack in the basement. It's an understandable impulse, and sealing does have a role, but on its own it rarely solves a radon problem. This guide explains what EPA says about sealing, which do-it-yourself steps are worthwhile, and when it's time to bring in a professional.

What EPA says about sealing

EPA's Consumer's Guide to Radon Reduction is direct: EPA does not recommend using sealing alone to reduce radon, because by itself sealing hasn't been shown to lower radon levels significantly or consistently. EPA gives two reasons:

1. It's hard to find and permanently seal every place where radon enters. Radon moves through tiny cracks, pores in concrete, gaps around pipes, hollow block walls, and floor-wall joints, many of which are hidden.
2. Houses move. EPA notes that normal settling opens new entry routes and reopens old ones.

Because a house acts like a gentle vacuum on the soil, any opening you miss will keep drawing radon in.

Where sealing does help

EPA also calls sealing cracks and other openings in the foundation a basic part of most approaches to radon reduction. In a professionally installed system, sealing:

• limits the flow of radon into the home;
• makes other techniques, especially sub-slab suction, more effective and cost-efficient, because the fan can create suction under the slab more easily;
• reduces the loss of conditioned air, which can lower the system's energy cost.

So sealing is a helper, not a cure.

DIY steps that are worthwhile

If you're waiting for a mitigator, or want to support a system you already have, these steps are reasonable:

• Seal the sump pit. An open sump is a large, direct path for soil gas. A gasketed, airtight sump cover, with sealed openings for the discharge pipe and wiring, is often part of a mitigation system anyway. Make sure the pump can still be serviced.
• Seal large, accessible cracks in the slab and foundation walls with a polyurethane caulk or sealant appropriate for concrete. Clean and dry the crack first.
• Seal gaps around pipes and conduits where they pass through the slab or walls.
• Cap or trap floor drains that connect to soil. Some drains can be fitted with water traps or one-way fittings, but don't block drains needed for flood protection.
• Cover exposed soil in a basement corner or crawl space with heavy plastic as a temporary measure.

After any DIY work, retest. If your level is still at or above 4 pCi/L, you need a real mitigation system.

What not to do

• Don't rely on paint-on sealers marketed as radon barriers as your only fix. Coatings may reduce moisture, but they don't address the pressure difference that draws radon in.
• Don't vent a homemade system at ground level or inside the house. EPA disallowed ground-level discharge because radon can re-enter the home and children could be exposed near the outlet.
• Don't install a fan inside the living space or basement. A leak on the pressurized side could push radon into the home.
• Don't seal combustion air openings or create backdrafting risks for furnaces and water heaters. That can create a carbon monoxide hazard.

Other non-suction methods EPA describes

Besides sealing, EPA's guide describes a few other techniques that can be used in any type of home. They're generally secondary options:

• House or room pressurization uses a fan to blow air into the basement or living area, from upstairs or outdoors, to create enough pressure at the lowest level to keep radon out. EPA's comparison lists basement pressurization at 50 to 99 percent reduction, but notes it works best in a tight basement isolated from the outdoors and upper floors. It can bring in outdoor air, with moisture and energy penalties, so EPA suggests considering it only after more common techniques haven't worked well enough.
• Heat recovery ventilation (HRV) brings in outdoor air while using exhaust air to warm or cool it. EPA describes its effectiveness as limited, and best suited to smaller areas like basements. The HRV filter needs cleaning and should be changed twice a year.
• Natural ventilation, such as opening windows, gives only temporary and variable reductions, with significant loss of heated or cooled air.

For most homes with levels at or above 4 pCi/L, active soil suction remains the most reliable approach.

Can you install your own radon system?

Some handy homeowners do install sub-slab systems themselves, and fan and pipe components are available to consumers. But there are good reasons to use a qualified mitigator:

• Diagnostics. Professionals test how suction spreads under the slab and pick suction points accordingly.
• Standards. National installation standards cover fan location, discharge height, labeling, and warning devices.
• Permits and state rules. Some states require licensed mitigators or permits for radon systems.
• Real estate. Buyers often want professional documentation and a post-mitigation test.
• Warranties. Many mitigators guarantee results.

EPA says most homes can be fixed for about the same cost as other common home repairs, and it advises getting estimates from one or more qualified contractors. Your state radon office can tell you about licensing or certification requirements.

The bottom line

Sealing is a smart supporting step, and sealing a sump pit or big cracks is a reasonable weekend project. But if your test is at or above 4 pCi/L, plan on an active mitigation system, usually sub-slab suction, and confirm the result with a post-mitigation test. See radon mitigation systems and hiring a radon mitigation contractor.

A sensible order of operations

1. Confirm the high result with a follow-up test.
2. Do the easy sealing: sump lid, large cracks, pipe gaps.
3. Get estimates from qualified mitigators.
4. Install an active system that fits your foundation.
5. Run a post-mitigation test, then retest at least every two years, as EPA suggests.