A Radon Test Is Not Required: When You Still Should
The phrase “a radon test is not required” usually surfaces in real-estate listings, FSBO disclosures, and lender checklists. The statement is technically true at the federal level: no national law mandates radon testing as a precondition of a residential sale. The statement is also misleading without context, because state disclosure rules vary widely and the absence of a legal requirement does not mean the absence of a strong public-health case. This guide summarizes EPA, HUD, and CDPHE guidance current as of 2026 and is not legal advice. Front Range buyers — Colorado is EPA Zone 1, the highest radon risk tier — almost always benefit from testing even when no rule requires it.
What “not required” actually means
Federal residential real-estate transactions have no radon-testing mandate. Single-family home sales between private parties, conventional financing, FHA financing, VA financing, and USDA financing all close without a radon test in most cases. HUD does not require radon testing for single-family FHA loans, though HUD does require it for multifamily transactions involving federal funds. The lender does not order a radon test the way the lender orders an appraisal. The buyer must request it, the buyer’s agent must include it in the contingency, and the buyer must pay for it.
State law layers on top of federal silence. Illinois requires sellers to disclose known radon hazards. New Jersey requires testing before mitigation system permits are issued. Maine requires landlords of certain residential rentals to test. Colorado as of 2026 requires no test, but it does require sellers to disclose results of any prior tests they are aware of. Disclosure-of-knowledge laws like Colorado’s create a strange incentive: a seller who never tests has nothing to disclose, while a seller who tests and gets a bad result must disclose it. The path of least resistance for sellers is sometimes to skip testing entirely, which transfers the question to the buyer.
Why the absence of a requirement doesn’t mean absence of risk
CDPHE estimates roughly half of Colorado homes test above EPA’s 4 pCi/L action level. EPA Zone 1 status — assigned to counties where average indoor radon is expected to exceed 4 pCi/L — covers the entire Front Range. The Surgeon General lists radon as the second leading cause of lung cancer in the United States after smoking, with an estimated 21,000 lung cancer deaths attributed annually. Among never-smokers, radon is the leading cause. None of these facts change based on whether a contract requires a test. The radon is in the soil regardless of what the listing agent put in box 14 of the disclosure form.
The companion is radon testing really necessary guide covers the clinical case in depth. The bottom line: in EPA Zone 1, the prior probability that any given home is above action level is roughly 50 percent. That’s coin-flip odds for a known carcinogen that takes 20 to 50 years to manifest as disease. Skipping the test because no one is forcing it does not change the underlying probability.
Real-estate context: when buyers should test anyway
Five real-estate situations warrant insisting on a radon test even when no rule forces one.
Front Range homes with basements
Basement bedrooms, basement family rooms, and basement home offices all create high-exposure occupancy. The lowest level of any Colorado home should be tested before purchase. The radon test basement placement guide covers test location selection in detail.
Pre-1990 construction without vapor barriers
Older foundations often lack the polyethylene vapor barrier under the slab that became standard practice in the 1990s. Soil gas pathways are correspondingly more open. Older homes also tend to have more crack development from decades of foundation settling.
Homes with sump pits or perimeter drains
Open sump pits are a direct soil-gas pathway. Even sealed pits are a higher-risk feature than a slab without a pit. Perimeter drain systems with daylight discharge can also act as radon entry pathways.
Homes with passive radon stack but no fan
Some Colorado homes built since 2009 include passive radon piping in the slab without an active fan. Passive systems are not always sufficient. Test to confirm the passive system is keeping levels below 2 pCi/L; activate the fan if not.
Any home where the seller refuses to disclose prior test results
If a seller declines to share whether prior testing occurred, that is information in itself. Buyers should treat the situation as if no test has ever been performed and order one as part of their inspection contingency.
When sellers should test before listing
Pre-listing testing benefits sellers when results are good. A documented passive 48-hour test reading 1.4 pCi/L in winter closed-house conditions is a strong marketing asset and removes the radon question from buyer-side inspection contingencies. The risk of pre-listing testing is the bad result that triggers disclosure obligations under Colorado law. Sellers facing that situation typically have two options: install mitigation before listing (cost: $1,200 to $2,500 for sub-slab depressurization on a Front Range single-family) and re-test, or disclose the elevated reading and price the home accordingly. Most listing agents recommend the install-and-disclose path because mitigation cost is recovered in the avoidance of buyer-side renegotiation.
The Colorado radon mitigation guide walks through installation cost ranges and what a defensible bid looks like. Sellers should secure at least two competitive bids before committing.
FHA, VA, and USDA loan situations
FHA loans for single-family residences do not require radon testing. VA loans for single-family residences do not require radon testing. USDA Rural Development loans for single-family residences do not require radon testing. All three programs do require radon testing for multifamily transactions where federal funds are involved, but most owner-occupied buyers fall under the single-family carve-out. The absence of a lender mandate does not preclude the buyer from ordering a test through the inspection contingency, which is the path most informed buyers take.
HUD’s Office of Lead Hazard Control and Healthy Homes publishes guidance recommending radon testing for any home being purchased with HUD-insured financing, even where the regulations don’t strictly require it. The recommendation has weight in fair-housing review and in HUD-funded grant programs. Buyers using HUD-related programs should treat the recommendation as effectively binding even when the contract language is silent.
What “Colorado does not require it” leaves on the table
Three things missing when no test occurs.
Baseline data for the homeowner’s records. A test today establishes the home’s radon level at a known point in time. Future renovations, occupancy changes, and seasonal patterns become interpretable against the baseline.
Documentation for future sale. A homeowner who tests today can disclose the test in a future sale and provide buyers confidence in the result. Untested homes face buyer-side testing demands every time they change hands.
Mitigation timing flexibility. A homeowner who learns about an elevated reading at purchase has 30 days to renegotiate or back out. A homeowner who tests two years post-purchase can plan mitigation on their own timeline without a closing-date pressure.
The disclosure trap
Colorado disclosure rules require sellers to share known radon test results. The rule does not require sellers to test in the first place. Some sellers reason that the absence of testing is better than the presence of a bad result. From a pure-disclosure standpoint that is technically correct. From an ethical and practical standpoint, the strategy mostly fails. Buyers in the Front Range overwhelmingly test during their own inspection contingency. The elevated result surfaces anyway, and now the buyer is the one with the bad news and the leverage. Sellers who pre-test and mitigate get to control the narrative. Sellers who avoid testing surrender that control.
The yes-no decision framework at should I test for radon walks through the buyer-side version of the same logic. Both sides of the transaction benefit from testing earlier rather than later.
References
- EPA Home Buyer’s and Seller’s Guide to Radon — U.S. Environmental Protection Agency
- HUD Radon Resources — U.S. Department of Housing and Urban Development
- CDPHE Radon Program — Colorado Department of Public Health and Environment
- EPA Radon and Real Estate — U.S. Environmental Protection Agency
Buyers and sellers along the Front Range can reach a vetted measurement professional for testing that meets EPA real-estate protocol, with chain-of-custody documentation and quick turnaround.