By Prerna Kapoor, CLHMS | REAL Brokerage | June 23, 2026
About half of all homes in Colorado have radon levels high enough that the EPA recommends doing something about them. That is not a scare statistic – it is just the reality of living on top of the kind of soil and rock we have here. The good news is that radon is one of the easiest home problems to find and fix, as long as you actually test for it.
If you are buying or selling a home in the Denver metro, radon is going to come up. Here is what it is, how testing works, and what to expect when it shows up during a transaction.
Why Colorado has a radon problem in the first place
Radon is a colorless, odorless gas that comes from uranium breaking down in soil and rock. It seeps up through foundation cracks, sump pits, and gaps around pipes, then collects in the lowest level of a home. You cannot see it or smell it, which is exactly why it gets ignored.
The reason it matters so much here is geology. The EPA classifies almost all of Colorado as Zone 1, its highest-risk category, meaning the average home is predicted to test at or above the action level. The Colorado Department of Public Health and Environment estimates that roughly half of Colorado homes have elevated radon. In Jefferson County, the county’s own data shows about 50% of homes test above the limit.
Radon is also the second leading cause of lung cancer in the country, behind smoking. That is the part that makes it worth a few days of testing rather than a shrug.
How radon testing actually works
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Testing is simpler and cheaper than most people expect. There are two main paths.
A short-term test kit runs for about three to seven days. You place it on the lowest occupied level of the home, two to six feet off the floor, and at least three feet from windows, doors, and vents so airflow does not skew the reading. The state sells kits through county health departments for around $10, which is hard to beat. You mail the kit to a lab and get a result back.
The second path is a professional continuous radon monitor, which is what most buyers use during a home purchase. A radon measurement pro sets up a calibrated machine for 48 hours and hands you a report. It costs more than a mail-in kit, usually in the low hundreds, but it is fast and harder to tamper with, which matters when money is on the line.
Radon is measured in picocuries per liter, written as pCi/L. The EPA action level is 4.0. If a test comes back at 4.0 or higher, the recommendation is to put in a mitigation system. Levels can swing with the seasons and the weather, so one high reading is not a reason to panic, but it is a reason to act.
How radon shows up in a real estate deal
In most Denver-area purchases, radon testing happens during the inspection period, often run alongside the general home inspection. The buyer pays for the test, and the results come back inside the inspection objection window.
If the level is at or above 4.0, the buyer can ask the seller to install a mitigation system before closing, or to credit the cost so the buyer can handle it after. Who pays is negotiable, and it usually comes down to the strength of the offer and how the rest of the inspection went. This is one of those line items that is easy to settle when both sides know it is coming, which is why I bring it up early with my clients rather than letting it surprise anyone at the table.
Radon testing is separate from the appraisal and the standard inspection, and it is not something the lender requires. It is a health and safety step, and in Colorado it is a normal part of doing your homework before you buy.
What mitigation looks like and what it costs
The standard fix is called sub-slab depressurization. A contractor runs a pipe from beneath the foundation slab up and out through the roofline, with an inline fan that pulls the gas out from under the house and vents it above the roof before it can get inside. It is not a teardown – most systems go in within a day.
In the deals I have worked around Parker, Aurora, and Castle Rock, mitigation quotes usually land somewhere between about $900 and $1,600, depending on the foundation and how the home is built. A retest afterward confirms the system brought levels down, and a good system will keep them down for years. Many homes here already have a passive radon pipe roughed in from construction, which makes adding a fan cheaper.
For sellers, here is the part worth knowing: if your home already has a system, say so up front. Buyers read a working radon system as one less thing to worry about, and it removes a negotiation point before it ever starts.
Quick answers
Is radon testing required when buying a home in Colorado?
No. It is not legally required and lenders do not demand it. But given that around half of Colorado homes test high, it is one of the smartest few hundred dollars you can spend during the inspection period.
Can I test for radon myself?
Yes. Short-term kits from the state run about $10 and are fine for a baseline check on a home you already own. For a purchase, most buyers use a professional 48-hour monitor because the result is faster and harder to dispute.
Does a high radon reading mean I should walk away from the house?
Usually not. Elevated radon is common here and the fix is routine and affordable. It is a reason to negotiate a mitigation system or a credit, not a reason to lose a home you love.
Prerna Kapoor | REALTOR® | Luxury Home Specialist
REAL Brokerage | 720-949-5450 | info@prernakapoor.com
CLHMS • RENE • PSA • ABR | International Sterling Society Award Winner
Prerna specializes in residential real estate across Parker, Aurora, Lone Tree, Castle Pines, Highlands Ranch, Cherry Creek, Greenwood Village, and Centennial. She speaks English, Japanese, and Hindi.
