Colorado's Radon Disclosure Requirement — and What Changed January 1, 2026

Radon disclosure is a Colorado-specific requirement (SB23-206, C.R.S. § 38-12-803), and it’s one more item that belongs on the same “before you sign a lease” checklist as the deposit cap and prohibited clauses — with a real change to how it works starting this year.

The core requirement: disclose before signing

Before a residential lease is signed, the landlord has to disclose, in writing, a bold-faced warning statement that the Colorado Department of Public Health and Environment strongly recommends every tenant have an indoor radon test performed before leasing, and recommends mitigation if elevated levels are found. This applies regardless of whether the landlord has ever actually tested the property.

What has to be disclosed if the landlord does know something

If the landlord has any knowledge of the property’s radon situation — whether a test has been conducted, the most current test records and reports, a description of any concentrations detected, and information about any mitigation system already installed — that has to be disclosed too. Silence is only an option if there’s genuinely nothing to disclose.

The tenant remedy — and what changed January 1, 2026

If a landlord fails to provide the required disclosures, or fails to make a reasonable effort to mitigate within 180 days of being notified that a radon measurement professional found a concentration of 4 picocuries per liter or more, a tenant has historically been able to void the lease and vacate.

As of January 1, 2026, that void-the-lease remedy no longer applies to a lease agreement of one year or less. For the majority of standard residential leases — a one-year term is the most common structure — this specific remedy is now narrower than it used to be. The disclosure requirement itself hasn’t changed; what changed is one particular consequence for failing to meet it, and only for shorter-term leases.

Why this is easy to miss

This sits in the same “required documentation” part of the statute as the landlord-name/address disclosure and signed-copy-delivery requirements covered in What Every Colorado Lease Must Disclose — but it’s a distinct disclosure with its own trigger and its own 2026 change, not just another line in that same checklist.

What to check in your own lease and process

• Does your lease packet include the bold-faced radon warning statement, not just a general environmental-disclosure mention?
• If the property has ever been tested, is that information — results, reports, mitigation history — actually disclosed to the tenant?
• Do you have a process for responding within 180 days if a tenant reports an elevated reading (4 pCi/L or more)?
• Does your understanding of the lease-voiding remedy reflect the 2026 change for leases of a year or less, not the pre-2026 rule?

The bottom line

The disclosure obligation itself is unchanged and still worth getting right regardless of lease length — the 2026 change narrows one specific remedy, it doesn’t loosen the underlying requirement to disclose. A Lease Template Review is a good place to confirm this disclosure is actually built into your standard packet.

LeaseCheck for Landlords is an educational lease-compliance screening tool. It is not a law firm and does not provide legal advice. Colorado rental laws change; confirm specifics for your situation with a licensed attorney.