7 Radon Findings That Stall a Colorado Home Sale

One out of every two homes in Colorado carries radon levels above the U.S. Environmental Protection Agency’s (EPA) action level, according to the Colorado Department of Public Health and Environment (CDPHE).

The tricky part is that radon has no smell or color.

These are the radon findings that stall a Colorado home sale.

Note: This is general information, not legal or environmental advice. Radon test levels, disclosure rules, and licensing requirements change, so confirm current guidance with CDPHE.

1. 4.0 pCi/L Line

A radon test crossing 4.0 picocuries per liter is the number that can decide whether a Colorado closing happens on schedule.

That’s the EPA’s action level, and about half of Colorado’s homes cross it.

The number decides everything.

The state’s standard purchase contract lets a buyer write in a radon contingency.

Boulder County‘s sample clause reads: “Contingent upon radon test being less than 4.0 pCi/L when conducted by a certified radon measurement professional.”

If the result comes back higher, the buyer can ask for mitigation, a lower price, or an exit from the contract before the inspection deadline closes.

A do-it-yourself kit from a hardware store works fine for peace of mind.

The contingency language calls for a licensed measurement professional instead, so the number holds up under a lender’s or a title company’s questions.

2. Disclosure Form Gap

A missing radon disclosure on a sale contract becomes a finding the moment a title company reviews the file.

Colorado sellers have had to give buyers a written radon disclosure since August 2023, and a contract missing that language raises a flag fast.

Senate Bill 23-206 requires the seller’s disclosure or the sale contract to state whether a radon test was ever done and share the most recent results.

It also has to describe any mitigation already performed and note whether a mitigation system exists.

Every residential contract must carry a bold warning about radon health risks, too.

The Colorado Division of Real Estate updated its forms the same week the law took effect, so a deal still running an old template is already out of date.

Skip any of it, and the sale contract falls out of compliance with state law, since Senate Bill 23-206 requires this disclosure in writing before the deal closes.

That’s a costly paperwork gap.

3. Undocumented Mitigation System

A radon mitigation system with no paperwork behind it is a disclosure problem waiting to surface.

Colorado’s disclosure form makes sellers report a mitigation system even when an earlier test read under 4.0 pCi/L, per the same Boulder County real estate guidance cited above.

The presumption is that if a system exists, radon was elevated at some point, and removing the system would let it return.

That’s the whole risk.

Radon levels also shift with the seasons and with how tightly a house is sealed.

A clean test from years back says little about a system a seller stopped running.

A buyer’s inspector who finds a fan or a vent pipe with no explanation can pause the deal until the paperwork catches up.

The paperwork decides how fast this moves.

4. Unlicensed Contractor’s Fan

A radon fan’s paperwork can name an unlicensed installer, a finding a title company catches by checking the state’s contractor list.

That mismatch can undo a closing almost as fast as a bad test result.

Colorado has required radon measurement and mitigation professionals to carry a state license through the Department of Regulatory Agencies since July 2022.

The license is the test.

A state license requires passing an accredited exam and following national field protocols, not just owning a fan and a drill.

Work done outside that system can draw fines, and it gives a lender or a buyer’s agent reason to ask for a second opinion before closing.

Working without that license can also draw a formal complaint filed with the state.

Homeowners use that same complaint process when a mitigation job never brings the reading below 4.0 pCi/L.

Unlicensed work rarely survives a title company’s second look.

5. Never-Retested System

A radon system nobody has retested in years is a finding some buyers catch and some sellers never think to check.

CDPHE recommends retesting a home's mitigation system every two years, since a fan can fail without warning while the reading creeps back up.

A fan that sounds fine can still be pushing air the wrong way, or barely moving any air at all.

The fan also runs on ordinary household power, so a system unplugged during a remodel can sit there looking installed while doing nothing.

A buyer's inspector who finds an old system with no retest record can ask for a fresh test before waiving the inspection objection deadline.

Old numbers don't count.

6. Untested Well Water

Radon in a private well is a separate problem from radon in the air, and many buyers never think to ask about it.

CDPHE advises testing the water supply for radon whenever a home on a well has already tested high in the air.

Many rural home sales run on well water instead of a city hookup.

Fixing a high water reading means an aeration system or a carbon filter built for radon, according to the EPA, not a standard whole-house water filter.

A high water reading calls for a different mitigation setup than an air system, and it can add time to closing while a buyer waits on results.

The clock resets for both.

7. New Build's Missing System

A new Colorado home missing its required radon system can stall a sale, the same as an old home with a bad reading.

Every Colorado county sits inside the EPA's highest radon-potential zone.

That's why some cities and counties require builders to install a passive radon-resistant system in every new single-family home, including six local governments across Boulder County alone.

That system routes soil gas through a vent pipe instead of letting it collect under the slab.

It's cheaper early.

No fan runs unless a retest after move-in comes back at 4.0 pCi/L or higher.