Selling a House With High Radon in Colorado

Nothing stalls a Northern Colorado closing quite like a radon number that lands above the line during the buyer’s inspection. It happens often here, because Larimer and Weld Counties both sit in EPA Radon Zone 1, the highest-potential tier, where the predicted average indoor screening level is greater than 4.0 pCi/L. If you are selling a house in Fort Collins, Loveland, Greeley, or anywhere in the region and a test came back high, you have decisions to make, and a state law that shapes how you make them.

NoCo Radon Pros is a free matching service. We do not test, install, or fix anything, and we do not hold a Colorado radon license. What we do is connect you with an independent, state-licensed local radon professional who can. This guide walks through the sales disclosure duty, the timing question, and the negotiation paths so you can go into the deal informed.

The disclosure trigger: what a Colorado sales contract requires

Colorado’s radon disclosure rules for property sales come from Senate Bill 23-206, effective August 7, 2023, codified at C.R.S. 38-35.7-112. The transaction itself is the trigger. Two things happen on every residential real property contract:

• The contract must carry a bold-faced warning recommending the buyer get an indoor radon test before the purchase and mitigate if the level is elevated.
• The seller must disclose known radon information. That includes whether a test was ever performed, the most recent records or reports, any concentrations that were detected, any mitigation that was done, and whether a mitigation system is installed. The seller also provides the buyer the current CDPHE radon-in-real-estate brochure.

So a high result you already know about is not something you can quietly set aside. Once a test exists, it is part of what you disclose. The state’s own resource page, CDPHE radon and real estate, lays out the seller and buyer materials. For a fuller walkthrough of the disclosure mechanics, see our Colorado radon disclosure law guide.

This is a summary, not legal advice. For how the statute applies to your specific contract, talk to your agent or a real estate attorney.

Mitigate before listing, or handle it in the deal?

There is no single right answer, and both approaches close houses every week in Northern Colorado.

Mitigating before you list

Fixing the radon before the sign goes up has real advantages. You control the timeline instead of the inspection clock. You can market a home that already tests below the EPA action level. And you remove a bargaining chip the buyer would otherwise hold. When a system is already in and the retest is clean, radon shifts from a problem to a non-issue, and sometimes to a selling point.

A mitigation system is a permanent improvement that stays with the house. Buyers who have done their homework in a Zone 1 county often see an installed system and a recent clean test as a plus, not a red flag. It signals the issue was addressed properly by a licensed professional rather than left for them to sort out.

Handling it during the deal

If the high result surfaces during the buyer’s inspection, you can still resolve it inside the transaction. This is the more time-pressured path, since the fix now competes with financing deadlines and closing dates. A standard sub-slab installation is usually quick to schedule and complete, but crawl space or more complex homes can take longer, so the calendar matters.

Whichever route fits your situation, the work is performed by an independent, state-licensed radon mitigation contractor, not by this brand. We can connect you with one who handles transaction-timeline installs. You can also read how the actual reduction work is done on our radon mitigation service page.

Your negotiation options when the number comes back high

When radon shows up during a deal, sellers and buyers typically land on one of a few outcomes:

1. Seller mitigates. You arrange the installation and a post-mitigation retest before closing, then hand over the documentation. This is often the cleanest resolution because it removes the uncertainty for everyone.
2. Seller credits. You give the buyer a closing credit toward mitigation and let them arrange the work after they own the home. This shifts the scheduling off your plate but leaves the buyer to vet the contractor.
3. Price adjustment. You reduce the sale price to reflect the fix. Buyers sometimes prefer this, but it is usually the bluntest instrument, and it can cost more than the actual system.

On cost, a system is often the cheaper concession than a comparable price cut. For most Northern Colorado homes a standard sub-slab system runs $1,000 to $2,500, with about $1,500 common. Crawl space setups (a vapor barrier plus fan tie-in) run higher, roughly $2,000 to $5,000 depending on size and condition, and difficult inaccessible crawl spaces can run more. Our radon mitigation cost guide breaks down the bands. Comparing the system cost against a straight price reduction is often the whole negotiation in a nutshell.

The post-mitigation retest that closes the loop

A mitigation system is only proven once a test confirms it worked. After installation, a Colorado-licensed radon measurement professional runs a post-mitigation test to verify the level dropped below the EPA action level of 4.0 pCi/L. EPA advises fixing at 4.0 pCi/L or higher, so a clean retest is what turns “a system is in” into “the home now reads below the action level.”

That written retest result is also exactly the kind of record you disclose to the buyer. It documents the concentration before, the mitigation performed, and the outcome after. In a Zone 1 market where testing is the only way to know a specific home’s level, a recent clean number carries weight at the closing table.

Remember that Colorado licenses radon professionals under HB21-1195, and both the measurement and the mitigation are done by those licensed pros, never by us. You can verify any contractor’s license on the state’s DORA license lookup before hiring.

Timeline pressure is the real variable

Radon rarely kills a Northern Colorado deal on its own. What creates stress is the calendar. Inspection objection deadlines, financing contingencies, and a scheduled closing all compress the window for scheduling an install and a retest. That is the strongest argument for testing early, ideally before you list, so a high result becomes a project you manage rather than a fire drill during escrow.

If you are earlier in the process and have not tested yet, start with our radon testing service page. If you want the broader statutory picture, including how sales and lease rules differ, the Colorado radon law guide is the pillar that ties it together.

How to move forward

Selling with high radon in Colorado comes down to three moves: disclose what you know, decide whether to fix it before or during the deal, and confirm the fix with a retest below 4.0 pCi/L. NoCo Radon Pros stays in one lane through all of it. We connect you with the Colorado-licensed radon professional you are matched with, at no cost to you, and we never perform or license the work ourselves. When you are ready, reach out and we will help you get matched.

This is a summary, not legal advice. For questions about your contract, disclosures, or obligations, consult your real estate agent or an attorney.