What should you do about a high radon test result in a Denver home sale?
Radon in a Denver home sale is usually a fixable item. The timing of your written objection decides how much room you have to negotiate.
For example, say you’re on day 7 of your inspection period on a home in Lakewood. The radon report comes back at 7.2 pCi/L. That’s well over the EPA’s action level of 4 pCi/L, and your Inspection Objection Deadline is three days away.
Here’s the local number that surprises people. The Colorado Department of Public Health and Environment (CDPHE) says nearly half of Colorado homes have radon above the EPA action level. In Jefferson County, the county health department puts it at about 50% of homes. So a high result on the Front Range is common, and so is the fix.
This post shows what the number means, what Colorado law requires sellers to disclose, how a radon result moves through the contract’s inspection deadlines, and the ways buyers and sellers usually settle it.
What the Radon Number Means
Radon is measured in picocuries per liter of air (pCi/L). The EPA recommends fixing a home at 4 pCi/L or higher and suggests you consider a fix between 2 and 4 pCi/L, because no level of exposure is known to be safe. For context, the EPA puts the average indoor level in U.S. homes at about 1.3 pCi/L.
The Colorado contract carries its own warning. Section 10.13 of the Contract to Buy and Sell Real Estate (Residential) says the state health department strongly recommends that all home buyers have an indoor radon test before buying, and recommends mitigation if elevated levels are found.
How a Real Estate Radon Test Works
Boulder County’s radon guidance describes real estate tests that run at least 48 hours in the lowest part of the home that could be lived in, usually the basement. A real estate test usually takes 2 to 7 days from start to report. That timeline matters, because your Inspection Objection Deadline doesn’t move while you wait.
Since July 1, 2022, Colorado has required radon measurement and mitigation professionals to be licensed, under a program created by House Bill 21-1195. You can check any tester’s or mitigator’s license through the Colorado Department of Regulatory Agencies (DORA) license lookup.
What Colorado Sellers Have to Disclose
Senate Bill 23-206, signed June 5, 2023, took effect August 7, 2023. It requires a residential sale contract to include a radon warning, the seller’s known radon history, and the most recent CDPHE radon brochure.
According to the Colorado Division of Real Estate’s August 4, 2023 broker advisory, the seller has to address:
- Whether any radon test has been done on the property
- The most recent test records or reports
- Any radon detected, and any mitigation or remediation done
- Whether a radon mitigation system is installed
- A copy of CDPHE’s brochure, Radon and Real Estate Transactions in Colorado
If you’re selling in Denver, Aurora, or Centennial and you tested five years ago, that result belongs in your disclosure. If a system is already in the basement, say so and hand over the paperwork. An installed system with records answers the question before a buyer asks it.
How a Radon Result Fits the Colorado Inspection Deadlines
Section 10.3 of the 2026 contract gives the buyer two paths, and the choice has consequences.
Path One: Terminate
Under Section 10.3.1, a buyer who’s unhappy with the inspection can deliver a written notice to terminate by the Inspection Termination Deadline. That right expires once the buyer delivers an Inspection Objection. You can’t object first and then terminate under this section later.
Path Two: Object and Negotiate
Under Section 10.3.2, the buyer delivers a written description of the unsatisfactory condition, such as a radon result of 7.2 pCi/L, by the Inspection Objection Deadline. This is where the radon test timing bites. If the report isn’t back in time, you can’t object to what you haven’t seen.
The Inspection Resolution Deadline
Section 10.3.3 sets what happens next. If the buyer and seller haven’t agreed in writing by the Inspection Resolution Deadline, the contract terminates on that deadline unless the seller receives the buyer’s written withdrawal of the objection.
So a seller who refuses to address radon isn’t the end of the story. The buyer still decides whether to walk or withdraw. If you’re facing that point, this guide on what happens when a Colorado seller refuses an inspection objection walks through it.
The Three Ways Radon Usually Gets Settled
Colorado law requires disclosure. It doesn’t require a seller to pay for mitigation. Who pays comes down to the negotiation.
| Option | How it works | What to watch |
|---|---|---|
| Seller mitigates before closing | Seller hires a licensed mitigator and pays for the system | Ask for the license number, the system details, and a follow-up test result |
| Closing credit | Seller credits the buyer at closing; buyer hires the mitigator after moving in | Lenders can limit seller credits, so check with your lender |
| Price reduction | The price drops by an agreed amount | Can lower the loan amount; buyer still pays for the system out of pocket |
Getting the Mitigation Cost Right
The EPA says most homes can be fixed for about the same cost as other common home repairs, and that the cost depends on the home’s size and design. Jefferson County Public Health puts typical repairs at about $1,250 to $1,500. Your actual number comes from a written bid, so get one or more from licensed mitigators before you put a dollar figure in your objection.
For example, on a $600,000 home in Littleton with an assumed $1,400 bid, a buyer might ask for a $1,400 credit or for the seller to install the system before closing. A seller might prefer the credit, so the work isn’t on their calendar during the move. That’s an example only. Bids vary by foundation, crawlspace, and finished basement.
Why Buyers Often Prefer the Credit
When the seller mitigates, the seller picks the contractor and the scope. A buyer who takes a credit picks the mitigator and can ask for a guarantee that the result lands below 4 pCi/L. A seller who installs the system can close that gap by sharing the bid and the post-installation test.
How Jamie Handles Radon in a Denver Sale
Jamie Bridges, a REALTOR® with Keller Williams Realty DTC, works with buyers and sellers across Denver, Aurora, Lakewood, Centennial, and Littleton, in both Arapahoe County and Jefferson County. He holds the Accredited Buyer’s Representative (ABR) and Seller Representative Specialist (SRS) designations. For buyers, he schedules the radon test on day one of the inspection period so the report lands before the Inspection Objection Deadline. For sellers, he asks for every past radon test and any system paperwork at the listing appointment, so the disclosure is complete before the first showing.
Radon disclosure and contract deadlines carry legal weight. A real estate attorney can tell you how they apply to your contract.
Frequently Asked Questions
Is a Colorado seller required to fix high radon? No. Senate Bill 23-206 requires sellers to disclose known radon test results, any mitigation, and whether a system is installed, and to provide CDPHE’s brochure. Paying for mitigation is a matter for negotiation under the inspection section of the contract.
What radon level should worry a Denver buyer? The EPA recommends fixing a home at 4 pCi/L or higher and suggests considering a fix between 2 and 4 pCi/L. A result above 4 is common on the Front Range, and it’s a fixable condition.
Can I still buy a home with high radon in Denver? Yes. Most buyers handle it through the Inspection Objection process, with the seller installing a system, giving a credit, or lowering the price. You can also mitigate after you move in.
If you’re buying or selling in Denver, Aurora, Lakewood, Centennial, or Littleton, a radon test planned around your contract deadlines saves you from a rushed decision. Jamie Bridges is a REALTOR® with Keller Williams Realty DTC serving the Denver Metro Area and Summit County, Colorado. Call or text Jamie at 720-397-7555 to talk about your next move.
Sources: U.S. EPA, “What is EPA’s Action Level for Radon and What Does it Mean?”, last updated October 13, 2026; U.S. EPA, “How much can a radon mitigation system cost?”, last updated September 16, 2026; CDPHE press release, “Radon causes lung cancer: test your home,” January 7, 2025; CDPHE, Radon and Real Estate Transactions in Colorado page, accessed October 30, 2026; Jefferson County Public Health, Radon, last updated June 9, 2026; Boulder County, “Radon in the Real Estate Transaction,” April 1, 2026; Colorado General Assembly, SB23-206, signed June 5, 2023, effective August 7, 2023; Colorado Division of Real Estate, “Broker Practice Advisory: SB23-206 and Changes to the Commission Approved Contracts,” August 4, 2023; Colorado Real Estate Commission, Contract to Buy and Sell Real Estate (Residential), CBS1, mandatory use January 1, 2026, Sections 10.3 and 10.13, accessed October 30, 2026; Colorado Department of Regulatory Agencies, “Radon professional licensure now required in Colorado,” August 16, 2022; Colorado Department of Public Health and Environment, Colorado Environmental Public Health Tracking, “Regulation of Radon Professionals: House Bill 21-1195,” September 30, 2021. Data deemed reliable but not guaranteed. General information only. This isn’t legal advice. Dollar figures labeled as examples are examples only.
