Since August 7, 2023, Colorado law (SB23-206, codified at C.R.S. §38-35.7-112) has required every residential real estate sales contract in the state to carry a bold-faced radon warning, and requires sellers to disclose what they know about a property's radon history. A related update took effect January 1, 2026, narrowing a tenant's lease-voiding remedy for undisclosed radon. Most of this still isn't widely known — a title company was still writing explainers for real estate agents about it in October 2026, three years after it took effect.
Every residential sales contract must include a bold-faced warning that the buyer "has the right to be informed of whether the property has been tested for elevated levels of radon." The seller must disclose what they actually know: whether the property has been tested, the most recent results and reports, any detected concentrations, and whether a mitigation system is installed — plus a copy of CDPHE's own radon brochure. What the law does not do: it does not require a seller to test before selling. A seller who has simply never tested only has to disclose that fact. The same written-disclosure requirement applies to residential landlords, not just sellers.
Source: C.R.S. §38-35.7-112 and SB23-206 (signed by Gov. Polis, effective August 7, 2023). The Colorado Real Estate Commission separately sets the exact contract-form language and delivery rules.
If a landlord doesn't provide the required radon disclosures, or doesn't address a known elevated reading, a tenant can void the lease under Colorado's implied-warranty-of-habitability statutes. As of January 1, 2026, that specific remedy applies only to leases longer than one year — a real, dated change to the original 2023 law, not something carried over from when SB23-206 first passed.
Source: SB23-206's own text. We haven't found independent reporting on how this change is playing out in practice yet.
RadonScout tracks Colorado's roster of state-licensed radon testing and mitigation professionals, sourced from the Colorado DORA licensee roster. See contractors serving Denver → Colorado also requires radon testing in public schools and licensed child care — see our Colorado school & daycare radon data →