Colorado Radon Disclosure: What the Contract Says and What to Do When the Test Comes Back High

Jerad Larkin

1 day ago

8 min read

What does Colorado require when a home with radon is bought or sold?

Since August 7, 2023, Colorado residential contracts carry a state radon warning, and sellers must give buyers any known radon test results, mitigation history, and the CDPHE radon brochure. Testing itself is not required.

Radon is the inspection item most Denver agents handle by habit. The buyer's inspector offers a test, the number comes back, and then everyone scrambles to work out what the contract says about it.

The short version: the contract says less than most agents assume. There is a required warning, a required seller disclosure, and no radon-specific deadline. Everything after that is negotiation, and negotiation goes better when you know the numbers before the test result lands.

This post covers what Colorado law and the 2026 contract actually require, the numbers worth quoting to clients, and a seven-step plan for the day a buyer's test comes back at 4.0 or higher. Bookmark it for your next inspection period.

As an Account Executive with Chicago Title of Colorado, I work with Denver Metro agents on the timelines that surround a closing. Radon is not a title issue (more on that below), but a mitigation job that is not finished before closing can still push a closing date, so it is worth planning for early.

The Numbers Worth Quoting to Clients

Colorado's health department said it plainly in a January 5, 2026 release: approximately half of Colorado homes have radon levels above the EPA action level of 4.0 pCi/L. Here are the figures I would keep handy.

4.0 pCi/L is the EPA action level. The EPA's citizen's guide says to fix a home at 4 pCi/L or higher, to consider fixing between 2 and 4, and notes that levels below 4 still pose some risk.
About half of Colorado homes are above 4.0. One Front Range testing company, Protect Environmental, reports 44 percent of its results at or above 4.0, with another 22 percent between 2 and 4. That is one company's results, not a random sample, so treat it as directional.
About 21,000 lung cancer deaths a year. That is the EPA's national estimate for radon, which is why the contract warning reads the way it does.
Roughly $1,300 to $3,000 for a typical system. Protect Environmental attributes that range to CDPHE for an existing single-family Colorado home. Installation usually takes about a day, followed by a verification test. Foundation type and access change the price, so get local quotes.

Radon does not follow city limits or neighborhood lines. A test at the house next door tells you very little about the house you are selling or buying, so quote the statewide numbers and test the actual property.

What Colorado Law Requires (SB23-206)

Senate Bill 23-206 took effect on August 7, 2023. The Division of Real Estate walked through the contract changes in a Broker Practice Advisory. Here is what it set up:

Two bold warnings in residential contracts. The first says CDPHE strongly recommends that every home buyer have an indoor radon test before purchase. The second calls radon a Class A human carcinogen and the leading cause of lung cancer in nonsmokers.
Seller disclosure. The seller discloses whether the property has been tested, the most recent results, any mitigation work, and whether a mitigation system is installed.
The CDPHE brochure. The seller provides a copy of the state's radon informational brochure.
Four updated forms. The Division updated the Contract to Buy and Sell (Residential), the Income-Residential contract, the Residential contract for the Colorado Foreclosure Protection Act, and the Seller's Property Disclosure.

Notice what is missing. The law requires warning and disclosure, not testing. A seller who has never tested simply discloses that.

Where it sits in the 2026 contract

In the CBS1 Contract to Buy and Sell (Residential)%20V2%20(fillable)_for%20use%20on%20or%20after%20January%201,%202026.pdf) version for use on or after January 1, 2026, the radon warning appears in Section 10.13, and the Seller's Property Disclosure ties to Section 10.1. As I read the form, there is no radon-specific testing deadline, objection process, or termination right. A radon test rides on the same inspection period and inspection objection deadline as every other inspection item.

That is the practical takeaway. If a buyer wants a radon test, the clock that matters is the inspection objection deadline in their contract, so the test gets ordered the day the contract is signed, not the day before the deadline.

This is education, not legal advice. For how the contract applies to a specific file, check with your managing broker or an attorney.

The Seven-Step Plan When a Buyer's Test Comes Back High

Say a buyer's test comes back at 5.8 pCi/L with a few days left before the inspection objection deadline (example numbers, not a real file). Here is the order I would work in.

Get the full report, not just the number. Ask for the device type, the test length, where it was placed, and whether the home was kept closed up during the test. A result is only as good as how the test was run.
Check the conditions against EPA guidance. The EPA says short-term tests run from two days to 90 days depending on the device, that windows and outside doors should be closed at least 12 hours before a 2 to 3 day test, and that the kit belongs on the lowest lived-in level in a room used regularly. A kit in an unused corner is a weak basis for a negotiation.
Decide on a retest the day the first number lands. If the conditions were off, or the result sits close to 4.0, a second test may be worth it. Short-term tests take days, so this decision cannot wait for the deadline week.
Get two mitigation quotes in writing. Use the cost range above as a sanity check only. Ask what the price includes, especially the verification test after installation.
Pick the ask. The common options are seller-installed mitigation before closing, a credit at closing, or a price adjustment. The seller can agree, counter, or decline. Which one fits depends on the timeline and the loan.
Call the lender before you write the ask. Colorado Lending Team notes that a standard mortgage does not always require a radon test, that program requirements vary, and that mortgage rules limit how seller credits can be used. I am not going to give payment math here. Your buyer's lender can tell them how a credit or repair escrow works on their loan.
Put it in writing, then verify the fix. Use the contract's objection and resolution paperwork. After installation, get the verification test results to the buyer. CDPHE recommends retesting every two years once a system is in place.

If You Are the Listing Agent: Test Before the Photos

The EPA's advice to sellers is blunt: test for radon now and save the results in case a buyer is interested. In Colorado, where known results have to be disclosed anyway, that advice has extra weight.

Order a short-term test before you list. The number belongs to you before it belongs to a buyer's inspector.
If it is elevated, get quotes and choose a lane. Mitigate before listing, or price and disclose with quotes in hand. Both are legitimate. Leaving it out is not.
Fill out the Seller's Property Disclosure from the records. Attach the CDPHE brochure and any prior test reports.
Keep the verification report from any installed system in your listing folder. The next buyer will ask for it.

Two numbers on paper beat a surprise in the middle of an inspection period.

Two Scripts You Can Use This Week

For a buyer client

"The state recommends every buyer test for radon, and about half of Colorado homes come in above the EPA action level. A high number is a normal negotiation item, and the fix usually takes about a day. Let's order the test the day we go under contract so we have time to act on it."

For a seller client

"I would rather we find the number before a buyer does. If we test before we list, we can decide how to handle it on our timeline instead of inside an inspection deadline."

What Radon Is Not: Title, Insurance, and Your Loan

Radon is a physical condition of the home, so it is not a title matter. Title insurance protects against ownership and recorded-document problems, which I cover in my guide to what title insurance is in Colorado. Whether a homeowners policy responds to anything radon related depends on the policy, so send that question to the client's insurance broker. The insurance market is already a deal risk this year, and I wrote about it in Colorado Homeowners Insurance Is Now a Deal Risk.

On the loan side, there is no universal radon rule across FHA, VA, conventional, and USDA. Ask the lender early, and do not assume a clean appraisal covers it.

Add a Radon Pro to Your Vendor List

If you keep a vendor bench, a radon testing and mitigation pro belongs on it next to your sewer scope contact. I made that case in my post on building a vendor referral network. It is far easier to vet someone before the week you need them. Ask:

What training and certifications do you hold?
How fast can you install after an accepted request?
Does the price include the post-installation verification test?
Will you talk directly with a seller's agent and send me a report I can forward?

Inspection items are also where Q4 deals wobble. I covered how to keep a contract alive in Your Q4 Income Is Already Under Contract, and if a mitigation job pushes a closing close to a holiday, run the dates in Q4 2026 Closing Date Math.

Quick Reference Checklist

Order the radon test on day one of the inspection period.
Ask for the full report and test conditions, not just the number.
4.0 pCi/L is the EPA action level. Consider fixing between 2 and 4.
Get two written mitigation quotes before you write the ask.
Call the lender before you propose a credit.
Save the verification test results for the file and the next sale.

Frequently Asked Questions

Is a radon test required to buy a home in Colorado?

No. Colorado law requires a radon warning in residential contracts and seller disclosure of known radon information, but it does not require a test. CDPHE strongly recommends every buyer test, and lender requirements vary by loan program.

What radon level is too high?

The EPA action level is 4.0 pCi/L. The EPA recommends fixing a home at 4.0 or higher and says to consider fixing between 2 and 4. It also notes that levels below 4 still carry some risk.

How much does radon mitigation cost in Colorado?

Protect Environmental attributes a range of roughly $1,300 to $3,000 to CDPHE for a typical system in an existing single-family Colorado home. Foundation type, access, and system design change the price, so get at least two quotes.

How long does radon mitigation take?

A typical installation takes about a day, followed by a verification test, according to Protect Environmental. Build that into the closing timeline if the seller is doing the work.

Who pays for radon mitigation in a Colorado home sale?

The contract and the negotiation decide. A seller can complete the work, offer a credit, or decline. If a credit is involved, the buyer's lender can explain how it can be used on their loan.

Keep Your Inspection Period Moving

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