Does Colorado law require radon mitigation before I sell my house?

No. Colorado sales law (C.R.S. 38-35.7-112) requires disclosure, not repair. You must include a bold-faced radon warning in the contract, share what you already know about the home's radon history, and hand over the current CDPHE brochure. Whether a system gets installed is a negotiation between you and the buyer, usually driven by the inspection test result.

The buyer's radon test came back above 4.0 pCi/L. What are my options?

Common paths in Northern Colorado are the seller mitigating before close, the seller giving the buyer a credit at closing to handle it later, or a price adjustment. EPA advises fixing at 4.0 pCi/L or higher. A licensed installer can usually add a standard sub-slab system in a day or two, which is why pre-close mitigation is popular under a tight timeline.

How much does mitigation cost when I am selling?

For most Northern Colorado homes a standard sub-slab system runs about $1,000 to $2,500, with roughly $1,500 common. Crawl space or larger homes can cost more. Because the work is fast, sellers often complete it inside the inspection window. Prices come from the independent, state-licensed professional who sees the home, not from us.

Do we need to retest after a system is installed?

Yes. A post-mitigation test confirms the system pulled the level below the EPA action level of 4.0 pCi/L, and buyers and lenders often want that written confirmation before closing. Plan the retest into your timeline, since it takes time to run. Ask the licensed professional to schedule it so results are ready before the closing date.

Is NoCo Radon Pros a contractor?

No. NoCo Radon Pros is a free referral service and does not test, mitigate, or hold a Colorado radon license. An independent, Colorado-licensed radon professional does the work, and you can verify any license yourself through the state DORA lookup. That contractor sets the scope, price, and schedule directly with you.

Radon Mitigation Before Closing 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. An independent, Colorado-licensed radon professional can handle the work on a sale timeline, and the quote is free.

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 moving quickly matters. A scope and a schedule from a Colorado-licensed radon professional can come together 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.

What a before-closing timeline actually looks like

Every deal is different, but a radon fix that starts promptly usually fits inside a normal Colorado inspection-and-closing window. The working sequence looks like this:

Right after the result. Decide the path (mitigate, credit, or price adjustment) and, if mitigating, get a free quote from a licensed professional the same week. The quote visit is what locks the scope and the schedule.
The install. A standard sub-slab system is often a one-day job. Crawl space and multi-foundation homes take longer, so surface that early if it applies to the house.
The retest. The post-mitigation test runs after the system is on and takes a couple of days to produce a written result. This is the step sellers forget to budget for, and it is the one the buyer and lender want on paper.
Before the closing date. Deliver the retest report and the system documentation with your disclosure records, so the radon line item is closed before the final walk-through.

Add those steps together and the practical rule is simple: the earlier the licensed professional is on the calendar, the more room the retest has to finish before closing. If the window is genuinely too short, that is when the credit or price-adjustment paths earn their keep.

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.

Getting a radon quote on a sale timeline

NoCo Radon Pros does not perform radon work and does not hold a license. It is a free service for home sellers across Northern Colorado, and the work itself is done by independent, state-licensed radon professionals. 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 a licensed professional 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.

Radon Mitigation During a Home Sale in Northern Colorado