Colorado Radon Disclosure Law (SB23-206)

Two different statutes govern radon disclosure in Colorado, and confusing them is the fastest way for an agent or property manager to get the paperwork wrong. Senate Bill 23-206 took effect August 7, 2023, and it reaches four groups across Northern Colorado: home sellers, buyers, landlords, and tenants in Larimer and Weld Counties. Both counties sit in EPA Radon Zone 1, the highest-potential category, so these disclosures are not a formality here. This page lays out what each statute says, in plain terms, so you can point clients to the right requirement.

This is a summary, not legal advice. The controlling text lives in the statutes and the SB23-206 bill record, and specific situations should go to a Colorado attorney.

The two statutes, kept straight

SB23-206 wrote radon duties into two separate parts of Colorado law:

• Sales of residential real property: C.R.S. 38-35.7-112.
• Residential leases: C.R.S. 38-12-803.

Do not cite the sales section for a lease question or the lease section for a sale. They carry different obligations and, on the lease side, a tenant remedy that has no equivalent in the sales statute.

For sellers and buyers (C.R.S. 38-35.7-112)

Every contract for the sale of residential real property must now carry a bold-faced warning in the contract itself. The warning recommends that the buyer obtain an indoor radon test before purchase and mitigate if the result is elevated. This is the transaction trigger: the moment a home goes under contract, the disclosure clock is running.

Beyond the contract warning, the seller must disclose the radon information they actually know, which the statute frames as:

• whether the property has been tested for radon;
• the most recent records and reports about radon concentrations;
• any radon concentrations that were detected;
• any radon mitigation or remediation that has been performed;
• whether a radon mitigation system is currently installed.

The seller must also provide the buyer with the current CDPHE radon-in-real-estate brochure. Colorado’s health department publishes and updates that brochure on its radon and real estate page, so agents should pull the live version rather than reuse an old PDF.

A point worth making to buyers: disclosure is about what the seller knows, not a guarantee that the home is safe. A house with no prior test simply means no data exists yet, and the absence of a disclosed number is not the same as a clean bill of health. Since about half of Colorado homes exceed the EPA action level, per CDPHE, a test during the inspection window is the only way to learn a specific home’s level. The full text of the sales requirement is posted at C.R.S. 38-35.7-112.

Agents in Northern Colorado should also note what the statute does not do. It does not force a seller to test a home they never tested, and it does not set a price or a deadline for mitigation. It sets a disclosure standard: put the bold-faced warning in the contract, hand over what you know, and deliver the current brochure. The negotiation over who pays for a test or a system happens in the contract terms, not in the statute. Keeping that distinction clear helps buyers understand that a quiet disclosure line often just reflects a home that has never been measured.

If a test comes back high mid-transaction, the timeline gets tight. Our guide on selling a house with high radon in Colorado walks through how sellers usually handle a result that lands during the contract period, and the radon mitigation at home sale service page covers the matching side when a system needs to go in before closing.

For landlords and tenants (C.R.S. 38-12-803)

The lease statute mirrors the sales duties at signing, then adds teeth. Before a tenant signs a residential lease, the landlord must provide, in writing:

• a bold-faced radon warning;
• any knowledge the landlord has about the property’s radon, meaning tests done, the most current records or reports, concentrations detected, and any mitigation performed;
• the current CDPHE radon brochure.

That is the lease duty, and it attaches at or before signing, not later. Property managers typically fold the warning and brochure straight into the lease packet so nothing is missed on move-in day.

The tenant void-lease right

Here is where the lease statute goes further than the sales statute. A tenant may void the lease and vacate the unit, following the process in C.R.S. 38-12-507, if either of two things is true:

1. the landlord failed to provide the required written disclosures; or
2. the landlord failed to make a reasonable effort to mitigate within 180 days after being notified that a radon measurement professional determined the radon concentration is 4 pCi/L or more.

The second path is important. It does not trigger on any home reading; it triggers on a licensed measurement professional’s finding of 4 pCi/L or higher, followed by written notice to the landlord, followed by 180 days without a reasonable mitigation effort. The 4 pCi/L figure is the EPA action level, explained on the EPA action-level page.

The January 1, 2026 carve-out

As of January 1, 2026, the void-lease remedy no longer applies to leases of one year or less in duration. In practical terms today: the remedy reaches leases longer than one year, and it does not reach leases of one year or less. The disclosure duty at signing still applies regardless of lease length; it is the vacate-and-void remedy that the carve-out narrows.

Non-compliance is a habitability breach

A landlord’s failure to comply with the disclosure requirements of C.R.S. 38-12-803 is treated as a breach of the implied warranty of habitability. That is a significant hook, because it pulls radon disclosure into the same body of remedies that covers other habitability failures. For property managers running units across Larimer and Weld Counties, the practical takeaway is that the radon warning and the CDPHE brochure belong in the standard lease packet, delivered before signing on every residential lease, so the habitability question never comes up. The full lease text is posted at C.R.S. 38-12-803.

Landlords who want the operational checklist should read our landlord radon obligations in Colorado guide, and when a rental needs work done, the radon mitigation for rentals page explains how we connect you with the right professional.

Who actually does the testing and mitigation

NoCo Radon Pros is a free matching service, not a contractor, and it does not hold a Colorado radon license. Colorado licenses the professionals who perform radon measurement and mitigation through the state’s Division of Professions and Occupations. Anyone signing a disclosure that references a test or a mitigation system should be relying on a state-licensed professional, and you can verify any contractor’s license on the DORA license lookup.

When a sale or a lease surfaces a radon question, we connect you with an independent, Colorado-licensed radon professional who can test the specific property or install a system. The license belongs to that professional, never to this brand.

Where to go next

For the wider picture of how Colorado regulates radon, including the licensing program and geology, see the Colorado radon law guide. To understand what a test number actually means before it lands in a disclosure, read radon test results explained. You can also start from the guides index or reach out through the contact page to get matched with a licensed professional.