You listed your house, accepted an offer, and everything was moving along until the buyer’s radon test came back above the EPA action level. Now the buyer wants a mitigation system, a retest before closing, and maybe a price concession on top. Or perhaps you tested the house yourself and the number on the report has you wondering whether a normal sale is even realistic.
We work with Colorado homeowners in exactly this situation. Below we explain why radon is so common along the Front Range, what Colorado law requires sellers to disclose, how a high result plays out in a traditional sale, and when selling as-is for cash makes more sense.
Why Colorado Is One of the Highest Radon States in the Country
Radon is not a defect in your house so much as a fact of Colorado geology. Much of the state sits on uranium-bearing granite and granite-derived soils, and as that uranium slowly breaks down it releases radon gas beneath our foundations. The gas rises through cracks in slabs, sump pits, crawl spaces, and utility penetrations, and accumulates indoors.
The EPA maps radon potential by county, and most Colorado counties fall into Zone 1, the agency’s highest-risk designation. Our climate makes it worse, because homes here are sealed tight against long winters, which limits the fresh air exchange that would otherwise dilute the gas. A brick bungalow in Denver, a post-war ranch in Lakewood, and a newer build in Colorado Springs can all test high, since the source is the ground rather than the age or condition of the structure.
What Radon Is and What the Numbers Mean
Radon is a naturally occurring radioactive gas, colorless and odorless, which is why the only way to know a home’s level is to test. According to the EPA, radon exposure is the second leading cause of lung cancer in the United States and the leading cause among people who have never smoked.
The number that matters in a sale is 4 picocuries per liter, or 4 pCi/L. That is the EPA action level, the point at which the agency recommends fixing the home. It is not a strict pass-or-fail line, but in practice it is the threshold buyers, inspectors, and agents treat as the trigger for mitigation talks.
Colorado’s Radon Disclosure Requirement for Sellers
Colorado tightened its rules in August 2023. Under state law, home sellers are now required to provide buyers with a radon disclosure, including a written warning about radon’s health risks and any knowledge the seller has of radon concentrations, past testing, or mitigation at the property. Landlords have a parallel obligation to tenants. The Colorado Department of Public Health and Environment publishes the current requirements and seller resources on its radon program page, and it is worth reviewing before you sign a listing agreement.
The practical takeaway is simple. If you have a high test result in hand, you cannot quietly set it aside and hope the buyer never asks. Known results travel with the house, much like known roof damage on the Colorado Seller’s Property Disclosure. CDPHE attributes roughly 500 lung cancer deaths in Colorado each year to radon, so this is a disclosure the state takes seriously and buyers increasingly understand.
How a High Radon Result Plays Out in a Traditional Sale
The inspection-period test
Most Colorado buyers now include a radon test during their inspection window, usually a 48-hour continuous monitor in the lowest livable level. Because so much of the state is Zone 1, elevated results are common, and a reading above 4 pCi/L typically arrives alongside the other inspection objections. You end up negotiating radon at the same time you may be negotiating a furnace, a sewer line, or hail-worn shingles.
Mitigation negotiations and retest anxiety
Buyers generally ask for one of three things: install a mitigation system before closing, credit them the cost to do it themselves, or reduce the price. If you agree to install, the work and a passing retest both have to happen before closing. Most systems perform well, but waiting on a retest with a contract hanging on the result is stressful, and a marginal reading can reopen the negotiation. If the deal falls apart, the result becomes part of the property’s known history and must be disclosed to the next buyer.
What Mitigation Involves
The good news is that radon mitigation is well-understood work. The standard fix is a sub-slab depressurization system, a sealed pipe through the slab connected to a continuously running fan that pulls soil gas from beneath the house and vents it above the roofline. For homes with crawl spaces, contractors seal the ground with a membrane and draw air from beneath it.
This is often a manageable cost, and if radon is the only issue standing between you and closing, hiring a licensed mitigation contractor is usually the right call. A mitigated home with a documented retest can be an easier sale than a never-tested one. The math changes when radon is one item on a longer list, which is where the as-is conversation begins.
Not sure what your high-radon Colorado house is worth as-is? Request a no-obligation cash offer or call us at (720) 213-8447, and we will review the property and explain the offer number by number.
When Selling As-Is for Cash Makes Sense
Some situations make the traditional route harder to justify. If a failed test surfaced mid-listing and cost you a buyer, relisting means new disclosure, new negotiations, and more weeks of carrying costs. If the result landed on top of other needed work, an aging roof, expansive-soil foundation movement, or moisture issues like those in our post on selling a Lakewood house with mold problems, the repair list can stack up faster than the sale price justifies. And if you inherited a never-tested home, an estate sale can stall while everyone waits on results and decisions.
Selling as-is for cash trades some potential upside for speed and certainty, and we think sellers deserve that stated plainly. A mitigated, market-ready home listed with an agent will usually bring a higher price than a cash offer. What a cash sale removes is the contractor scheduling, the retest anxiety, and the risk of a deal collapsing at the inspection table. We covered the broader tradeoffs in our guide to selling your home as-is in Denver.
How We Evaluate a House With High Radon
A high radon number does not scare us off, because we plan mitigation into nearly every Front Range purchase anyway. When James Heller and the Atlas team review a property, we look at location, condition, comparable sales, and the full scope of expected work, radon system included, then explain how we arrived at the offer. There are no commissions or fees, no repairs to complete first, and no retest contingency. The process starts with a conversation, moves to a walkthrough, and ends with a written offer within 24 hours, with a closing date you choose.
Common Questions We Hear
Do I have to fix radon before selling my house in Colorado?
No. Colorado law requires disclosure, not mitigation. You must give buyers the required radon warning and share what you know about testing and levels at the property, but you are not obligated to install a system. In a traditional sale, most buyers will negotiate for mitigation anyway. In a cash sale to us, we buy with the known result and handle mitigation ourselves.
Will a high radon test ruin my home’s value?
Generally no, because radon is so common across Colorado that buyers and investors treat it as a fixable condition rather than a fatal flaw. A documented system with a passing retest largely settles the issue for future buyers. Value suffers mainly when a high result combines with other deferred maintenance, or when a failed deal leaves a house sitting on the market.
Do you lower your offer because of radon?
We account for a mitigation system the same way we account for any expected work, and we will show you exactly how it factors in. Because mitigation is routine for us, radon alone rarely moves an offer much. Condition, location, and comparable sales matter far more, and we explain each piece so you can weigh our number against the listing route.
A radon report is unsettling to read, especially in the middle of a sale you thought was nearly done. Whether you mitigate, relist, or sell as-is, you have workable options. We have helped many Colorado homeowners move on from exactly this situation.
At The Atlas Portfolio, we buy houses as-is across Denver and the Front Range, we are straightforward about how we arrive at our offers, and we close on your schedule. Read what past sellers have said, see how our process works, and request a cash offer whenever you are ready.
