Radon Mitigation During a Home Sale in Northern Colorado
A radon result on an inspection report can stall a closing faster than almost any other line item, and in Northern Colorado it shows up often. Larimer and Weld Counties both sit in EPA Radon Zone 1, the highest-potential category, so when a buyer runs a test during the inspection period, an elevated number is a real possibility. NoCo Radon Pros is a free matching service. We do not test or mitigate and we do not hold a Colorado radon license. We connect you with an independent, Colorado-licensed radon professional who can handle the work on a sale timeline.
This is a summary, not legal advice.
What Colorado’s sales disclosure law actually requires
Colorado’s radon disclosure duty for home sales lives in C.R.S. 38-35.7-112, added by Senate Bill 23-206 and effective August 7, 2023. It is a disclosure law, not a repair mandate. Nothing in the statute forces you to install a mitigation system before you sell. What it does require is that the transaction put radon in front of the buyer clearly and honestly.
Under the sales statute, every residential real property contract must carry a bold-faced warning that recommends the buyer get an indoor radon test before the purchase and mitigate if the level is elevated. As the seller, you also disclose the radon information you already know. That includes whether the home has been tested, the most recent records or reports you have, any concentrations that were detected, any mitigation that has been performed, and whether a mitigation system is currently installed. On top of that, you provide the buyer the current CDPHE radon-in-real-estate brochure.
The key word is known. You are not required to go find new information or run a fresh test just to sell. You are required to be truthful about what already exists. If you have an old test result in a drawer or a system a prior owner installed, that gets disclosed. For the full statutory picture, our Colorado radon disclosure law guide walks through the sales and lease rules side by side, and the broader Colorado radon law guide covers licensing and the disclosure statutes together.
You can read the state’s own real-estate resources at CDPHE radon and real estate, and the bill text is posted at leg.colorado.gov.
How radon surfaces during a sale
Most radon issues in a transaction surface the same way: the buyer orders a radon test as part of the general home inspection. The test runs during the inspection objection period, and the result lands while both sides are still negotiating. If the number comes back at or above the EPA action level of 4.0 pCi/L, the buyer typically raises it as an inspection item.
Because Northern Colorado is Zone 1, sellers here should expect radon to come up more often than a national average would suggest. Statewide, about half of Colorado homes tested above 4.0 pCi/L according to CDPHE, and while that figure is a Colorado number rather than a Larimer or Weld number, it tells you an elevated result is common enough to plan for. Testing is the only way to know what a specific home will read. If you want to get ahead of the buyer’s test, our radon testing page explains how a pre-listing test works and what the numbers mean. For a deeper read on interpreting results, see radon test results explained.
Getting your own test done before you list is optional, but it removes surprises. If you already know the number, you can decide whether to mitigate in advance, price accordingly, or simply be ready to negotiate. A seller who is caught flat-footed by the buyer’s result during a tight objection window has fewer options than one who saw it coming.
Negotiation paths when a result comes back high
When a buyer’s test is elevated, sellers in Northern Colorado usually see three practical paths. None of them is required by law. They are simply the ways the parties tend to resolve it.
Seller mitigates before closing
The seller hires an independent, state-licensed radon mitigation contractor to install a system before the closing date, then provides a passing post-mitigation test. This is the cleanest outcome for a buyer and often the fastest way to keep a deal on track, because a standard sub-slab depressurization system can usually be installed in a day or two. For most homes the cost is about $1,000 to $2,500, with roughly $1,500 common for a standard sub-slab system. Our radon mitigation page explains how those systems work, and the radon mitigation cost guide breaks the pricing down further.
Credit to the buyer at closing
Instead of doing the work, the seller offers a closing credit so the buyer can arrange mitigation after taking possession. This keeps the seller out of scheduling and contractor coordination during an already busy closing, and it lets the buyer choose their own licensed professional. The credit is usually sized to the expected cost of a system.
Price adjustment
Sometimes the parties simply adjust the purchase price to reflect the radon issue and move on, leaving mitigation entirely to the buyer. This is common when the buyer wants control over the work or the timeline is too short to complete mitigation and a retest before closing.
Which path fits depends on your timeline, your buyer, and how the contract’s inspection provisions are written. For a fuller walkthrough of the seller’s side, our guide on selling a house with high radon in Colorado covers each option in more detail.
Timing is the real pressure
The hard part of radon in a sale is rarely the fix. It is the clock. The buyer’s test result often arrives late in the inspection period, which leaves a narrow window to decide on a path, get a licensed installer scheduled, complete the work, and run a post-mitigation retest, all before the closing date.
That is why matching quickly matters. When we connect you with an independent, Colorado-licensed radon professional, you can get a scope and a schedule fast enough to fit inside the objection window. Installation itself is quick, but a confirmation test takes time to run, so the earlier the professional is on the calendar, the less likely radon is to push your closing.
The post-mitigation retest
A mitigation system is not considered done until a follow-up test confirms it worked. The post-mitigation test verifies the system pulled the home’s level below the EPA action level of 4.0 pCi/L. In a sale, this written confirmation is what the buyer, and often the lender, wants to see before closing. You can read EPA’s explanation of the action level at what EPA’s action level means.
Build the retest into your timeline from the start. If mitigation is going to be part of the deal, the licensed professional should plan the confirmation test so results are ready before the closing date, not scrambled together at the last minute.
How the matching service works
NoCo Radon Pros does not perform radon work and does not hold a license. We are a free service that connects home sellers across Northern Colorado with independent, state-licensed radon professionals who do. The contractor sets the scope, the price, and the schedule directly with you, and you can verify any Colorado radon license yourself through the state’s DORA license lookup.
If you are getting ready to list, or a buyer’s test just came back high, reach out through our contact page and we will connect you with a licensed professional who can work on your sale timeline. You can also read how we make money so you understand exactly why the service is free to you.
Radon does not have to derail a Northern Colorado closing. With disclosure handled correctly under C.R.S. 38-35.7-112, a clear negotiation path, and a licensed professional lined up early, most sales absorb a high radon result and still close on time.