Finishing a basement in Columbus: test for radon first

Your Columbus basement is about to become a family room, an office or a guest bedroom, and the framing already has a date on the calendar. Radon belongs at the front of that schedule, because every stage after framing makes a mitigation system harder to route and harder to hide.

Before demolition: get a number to compare against

EPA's Citizen's Guide to Radon recommends testing before a major renovation such as finishing a basement, and again once the work is done. The first number tells you whether a system should be designed into the project. It also becomes the baseline for the test afterward.

Test the basement as it is today, in the part that will become living space. Ohio's measurement protocol puts the device in the lowest level suitable for occupancy, in a room that can be used regularly, and keeps it out of bathrooms, laundry areas and closets, with at least 10 feet of clearance from a sump pit. A hardware-store charcoal kit runs $15-$30. A professional short-term test on our price list runs $150-$300 and comes with a report showing where the device sat, when it ran, and who placed it.

Run the test before anyone tears out paneling, opens exterior walls or props windows open for dust, since those conditions break the closed-house setup a short test depends on. If the basement reads 4 pCi/L or higher today, finishing it will not change that; drywall and carpet do nothing to stop soil gas. Our FAQ on testing before you finish a basement goes further into timing.

Before framing: pick the pipe route while everything is visible

This is the stage that saves the most drywall. With the space open, the slab, the floor-wall joint, the sump and every mechanical penetration can be seen, which is exactly what the visual inspection and floor plan drawing under the Ohio Radon Mitigation Standards (ORMS) need. Where the fill under the slab is unknown, ORMS also requires a communication test before installation, and drilling test holes in a bare floor is far easier than drilling through new carpet.

The route is shaped by one hard rule. The fan can never sit in the basement or in any conditioned space, so the pipe has to leave the basement and reach an attic, a garage with no living space above it, or the outside of the house. In practice that produces three layouts:

• Up an interior chase, such as a closet or a stacked wall cavity, into the attic, with the fan there and the outlet through the roof.
• Out through the rim joist to an exterior wall, with the fan outside and a stack climbing past the highest eave.
• Into an attached garage with no bedroom over it, with the fan in the garage and the pipe continuing up through the garage roof.

Choose one before the studs go up, then frame around it. The main pipe is at least 3 inches across, so it needs a real chase, not a leftover gap behind a soffit. If the suction point falls where a bedroom wall is planned, move one or the other now.

Older housing adds its own wrinkles. In an Upper Arlington period revival house or mid-century home, the question is often whether a closet stacks cleanly above the basement or whether an exterior or garage route is simpler. Worthington mixes an older core with postwar neighborhoods, and the answer changes from house to house.

Before drywall: seal, label and leave access

With the route set, the details ORMS spells out go in while they are still easy to reach:

• The floor-wall joint gets urethane caulk, with backer rod where the gap is wider than half an inch. If the basement has a channel drain along the wall, the sealing leaves it able to carry water.
• Slab cracks and utility penetrations are sealed. Any opening that cannot be sealed has to be disclosed to you in writing.
• The sump gets an airtight lid with a view port, strong enough to stand on, sealed with silicone so the pump can still be serviced, and labeled. A pit with a working pump should not be the main suction point.
• Exposed pipe carries a RADON REDUCTION SYSTEM label on every floor it passes through, so the next owner, electrician or plumber knows what it is.

The cleanest sequence installs and activates the system before the drywall goes up, so a leak or a weak pressure reading can be fixed with the walls still open. Keep the manometer where you can see it. It is marked at its start-up reading, and a gauge buried behind a finished wall is a gauge nobody checks. If the pipe gets boxed in, leave an access panel at the gauge and at any cleanout.

Wiring for the fan and the warning device is a separate question. Electrical permits for a basement finish and for a radon fan circuit are set locally, so confirm with the building department for the property before the electrician roughs in. An exterior fan is hard-wired, with an outdoor disconnect in sight of the fan and within 4 feet of it.

Bedrooms and offices on the lowest level

The room plan changes who is exposed and for how long. A bedroom or a home office turns a basement that used to see laundry trips into a place where someone spends long, regular hours. Once someone sleeps or works down there, that finished room is the room that matters for radon.

EPA's Citizen's Guide makes the same point from the other side: if you begin using a lower level that you did not use before, retest on that level. Ohio's protocol already aims tests at the lowest level suitable for occupancy, so a new bedroom simply confirms where the device goes. If the basement already has a system, a new bedroom is a good reason to check that the fan is running and the gauge still reads where it was marked.

A typical active sub-slab system on our price list runs $1,200-$2,400. Designing it into the finish is the difference between a pipe hidden in a chase and one running across a freshly painted wall. The radon mitigation systems page describes what a standard install includes.

After move-in: test the room you now live in

Once the room is finished, furnished and in use, test again in that room. If a system went in during the project, Ohio requires that you be told in writing to test no earlier than 24 hours after the fan starts and no later than 30 days, by the mitigation specialist or an independent licensed tester. If no system was needed before, test anyway: the finished room is now the lowest level people occupy.

After that, the Ohio Department of Health recommends retesting single-family homes every two years or after a significant renovation, so a later bathroom or bar in the basement is its own reason to test again.

If demolition is a few weeks away, start the test this week. Then call or text us with the result and a rough sketch of the planned rooms, or get a first estimate from the calculator.