Radon and home renovations: when to test, what changes can raise levels, and how to plan

A renovation can change how your house breathes, and that can change your radon level, sometimes a lot. A tighter house, a new addition on a slab, a finished basement, or a new furnace can all shift the pressure balance that draws soil gas indoors. EPA's guidance recognizes this: its home buyer's guide notes a new test may be warranted if a home has been renovated or altered since the last test. This guide explains which projects matter and how to plan around them.

Projects that commonly affect radon

Finishing a basement. You'll start spending more time on the lowest level, which EPA says is a reason to retest there. Construction can also add new penetrations in the slab and walls.

Additions on slabs or crawl spaces. A new foundation creates a new soil-contact area that the existing mitigation system, if you have one, probably doesn't cover.

Energy-efficiency upgrades. Air sealing, new windows, and added insulation reduce drafts, which is good for energy bills, but they can also reduce dilution and change pressure patterns. Some tight homes see radon rise after weatherization.

New HVAC equipment. A new furnace, heat pump, or duct system can change pressures. Return ducts in basements or crawl spaces can pull soil gas into the air stream if they leak.

New exhaust fans or appliances. Larger kitchen range hoods, new bathroom fans, and clothes dryers exhaust air from the house, which can increase the vacuum on the soil.

Foundation repairs and slab work. Cutting the slab for plumbing, cracks from settlement, or a new sump can open new radon entry points.

Test before you start

Testing before a renovation gives you a baseline and lets you build radon reduction into the project:

• If levels are already high, you can install mitigation during construction, often more neatly and cheaply, with pipes hidden in new walls or chases.
• If levels are low, you'll have a baseline to compare against after the project.

Build radon-smart features into the project

• Seal slab and wall penetrations while they're exposed. EPA calls sealing a basic part of most radon reduction approaches, though not a fix on its own.
• Rough in a vent pipe in new additions on slabs: a gravel layer, a plastic sheet, and a capped pipe stub, similar to radon-resistant new construction. That makes adding a fan later straightforward.
• Plan the route for any future sub-slab pipe to the roof. EPA explains the discharge must be above the roof, because radon concentrations at the outlet are high and fall to background within a few feet.
• Seal ductwork in basements and crawl spaces, especially return ducts.
• Consider makeup air for large range hoods, so they don't depressurize the house.

Protecting an existing mitigation system

If you already have a radon system, construction can damage it or reduce its effectiveness:

• Tell your contractor where the pipe, fan, suction points, and manometer are.
• Don't reroute or cut the pipe without involving a qualified mitigator.
• Keep the fan running. EPA says the fan should never be turned off. It must run continuously.
• Protect the manometer and labels from being drywalled over.
• Watch for new slab openings, which may need to be sealed or connected to the system.

Test after you finish

Once the work is done and the house has returned to normal operation, with HVAC running and windows closed:

1. Run a short-term test in the lowest lived-in level under closed-house conditions.
2. If it's at or above 4 pCi/L, confirm it and fix it. If you already have a system, have a mitigator evaluate whether it needs another suction point or a larger fan.
3. Check the manometer reading against its pre-renovation value.

EPA's general guidance also suggests retesting if you start occupying a lower level, and periodically over time.

Additions and the existing system

A common situation: a house with a sub-slab system on the original basement adds a family room on a new slab. The new slab may sit on separate fill, with no air connection to the existing suction point. Options include extending the system with a new suction point under the addition, or installing a second system. Planning this before the addition's slab is poured is far easier.

Selling after a renovation

If you sell after a major renovation, expect buyers to ask for a recent test. EPA's buyer guidance lists renovations since the last test as a reason a buyer may want a new one. Testing after your project, and keeping the report, will help.

Talking to your contractor about radon

Bring radon up at the planning stage:

• Share your most recent test result and whether you have a system.
• Ask whether the work will penetrate the slab or foundation, and how openings will be sealed.
• For additions, ask the contractor to include a gravel layer, plastic sheeting, and a capped vent pipe stub under the new slab.
• Ask how new exhaust fans and range hoods will get makeup air.
• If you have a system, put "do not disturb radon pipe, fan or manometer" in the written scope.
• Schedule a radon test for after completion, once the house is back to normal operation.

Many general contractors aren't radon specialists. Bringing in a qualified mitigator for a short consultation during design can save money later.

Quick checklist

• Test before the project.
• Install or plan mitigation during construction if levels are high.
• Seal penetrations and rough in vent pipes for new slabs.
• Protect and keep running any existing system.
• Test after completion and keep the results.

Key takeaways

• Renovations can change how a house breathes and raise radon.
• Test before you start, so you have a baseline and can build in mitigation.
• Seal slab penetrations and rough in vent pipes for new slabs.
• Never turn off or reroute an existing radon fan without a mitigator.
• Test again after the project, once the house is back to normal operation.