Colorado doesn’t require radon testing before every home sale, but sellers must disclose known radon information on the standard Seller’s Property Disclosure form, and landlords are required under SB23-206 to provide written radon disclosures to tenants. Understanding these standards helps sellers, landlords, and real estate agents stay compliant and avoid delays during a transaction.
Radon disclosure sits at the intersection of public health policy and real estate law, and in Colorado it’s a topic that trips up sellers, landlords, and agents more often than it should. The rules are specific, the forms have changed, and the consequences of getting it wrong, including voided leases and habitability claims, are real. Whether you’re listing a home, renewing a lease, or helping a client through a transaction, here’s what Colorado law actually requires.
Does Colorado Require Radon Disclosure?
Colorado operates under a disclosure framework rather than a testing mandate. The state does not require sellers or landlords to test a property for radon before every transaction, but it does require them to disclose everything they know. That distinction is important: a seller who has never tested a property is not required to go test it before listing, but a seller who has test results on file is legally required to share them. The moment radon information exists, it must be disclosed.
For rental properties, the obligation is more structured. Under Senate Bill 23-206, which took effect on August 7, 2023, landlords have specific written disclosure requirements that apply to every new lease regardless of whether prior testing has occurred. For home sales, the Colorado Division of Real Estate updated its Commission-approved forms, including the Seller’s Property Disclosure, to reflect the new requirements under SB23-206. Both tracks, sales and rentals, flow from the same legislation but operate through different mechanisms and carry different consequences for non-compliance.
What Home Sellers Must Disclose About Radon
The Seller’s Property Disclosure Form
The Colorado Seller’s Property Disclosure, one of the Commission-approved forms updated when SB23-206 took effect, includes a dedicated Environmental Conditions section that specifically addresses radon. Sellers are required to disclose radon as a known hazard if it exists or has ever existed at the property, and this obligation applies even if prior test results came back below the EPA’s 4.0 pCi/L action level. The form asks whether tests have been conducted, what the results were, whether any mitigation or remediation has been performed, and whether a mitigation system is currently installed in the home. Each of these questions requires an honest answer based on the seller’s actual knowledge, and leaving them blank when information exists is not a compliant approach.
Disclosing Known Radon Test Results
Under Colorado Revised Statutes § 38-35.7-112, codified through SB23-206, every contract of sale for residential real property must contain a bold-faced warning statement from the Colorado Department of Public Health and Environment recommending that all buyers have an indoor radon test performed before purchasing. Beyond the warning, sellers must disclose any knowledge of the property’s radon concentrations, including the most recent records and reports pertaining to radon levels, a description of any concentrations detected or mitigation performed, and information about any installed mitigation system. Sellers are also required to provide the buyer with a copy of the most current CDPHE radon brochure. These aren’t optional extras; they’re legal requirements tied directly to the sale contract.
What Happens If a Seller Doesn’t Know Radon Levels
A seller with no prior test history is not in violation simply for not knowing. The disclosure obligation is tied to actual knowledge, so a seller who has genuinely never tested the property can indicate that on the disclosure form. However, if a previous owner tested the property and those records are available or discoverable, sellers should work with their agent to understand whether that information is within their constructive knowledge. Buyers, for their part, are strongly advised to order independent radon testing during the inspection period regardless of what the seller discloses, since the seller’s knowledge is only as reliable as the seller’s testing history. For buyers evaluating a home where a mitigation system is already in place, our post on buying a home with radon mitigation covers what to look for and what questions to ask.
What Landlords Must Disclose Under Colorado Law
For rental properties, SB23-206 created a clear statutory disclosure requirement that goes beyond simply answering questions on a form. Before a tenant signs a lease, landlords must provide a written disclosure document that includes a bold-faced warning statement substantially matching the CDPHE’s recommended language, any knowledge the landlord has of the property’s radon concentrations including test history and results, a description of any radon mitigation or remediation performed, information about any existing mitigation system including system documentation, and a copy of the most recent CDPHE radon brochure. The tenant must sign the disclosure to acknowledge receipt, creating a documented record that the disclosure was made.
The consequences for landlords who fail to comply are significant. If a landlord does not provide the required disclosures, or if a landlord fails to make a reasonable effort to mitigate within 180 days of being notified by a radon professional that concentrations are at or above 4.0 pCi/L, the tenant may void the lease. After January 1, 2026, this lease-voiding remedy applies only to leases longer than one year. Non-compliance with the disclosure requirements also constitutes a breach of the warranty of habitability under Colorado law, which creates additional legal exposure beyond a voided lease. For a complete breakdown of what these requirements mean in practice, our guide to Colorado radon landlord requirements covers the specifics in detail.
How Radon Disclosure Affects Real Estate Transactions
Disclosure and testing are related but separate events in a Colorado real estate transaction. A seller’s disclosure tells buyers what is already known; a buyer’s radon test during the inspection period finds out what isn’t. Even when sellers disclose clean prior test results, buyers commonly order new tests during the inspection period because radon levels can shift over time due to seasonal variation, foundation settling, or changes to the home’s HVAC or ventilation systems. A test result from five years ago does not reliably represent what today’s levels look like, and most experienced agents recommend fresh testing regardless of disclosure history.
When a test during the inspection period comes back at or above 4.0 pCi/L, the buyer has grounds to submit an inspection objection, and the negotiation process begins. Sellers may agree to install a mitigation system before closing, offer a credit toward the buyer’s closing costs, or negotiate other terms to address the issue. The seller’s prior disclosure record matters here: a seller who fully disclosed known radon information and a previously installed mitigation system is in a much stronger negotiating position than one whose disclosure was incomplete or inconsistent with test results the buyer uncovered. Understanding radon testing during home inspections and how results flow into the objection and negotiation process helps both sides navigate these situations efficiently.
Are There Tax Incentives Tied to Disclosure or Mitigation?
Sellers and landlords who invest in radon mitigation before or during a transaction naturally wonder whether those costs come with any tax relief. The answer depends on which programs are currently active and how a given system qualifies. There is no dedicated federal tax credit specifically for radon mitigation, and radon systems generally don’t qualify under energy efficiency credit programs since they address health rather than energy consumption. However, there are limited scenarios where mitigation costs may overlap with qualifying home improvement categories, and some state-level assistance programs exist for eligible homeowners. Our detailed breakdown of the radon mitigation tax credit landscape covers what’s currently available, what homeowners typically can and can’t claim, and how to approach this question with a tax professional.
Best Practices for Compliant Radon Disclosure
For sellers, the most defensible position is a documented testing history that is current, complete, and honestly reported on the disclosure form. A seller who tested the property within the past two years, has documentation of the results, and has either mitigated a prior elevated reading or can show a clean result goes into a transaction with significantly less disclosure risk than one relying on decade-old results or no testing history at all. Testing before listing, rather than waiting to see what a buyer’s inspector finds, eliminates the risk of surprises during the inspection period and gives sellers more control over the negotiation. For landlords, the practical starting point is building a disclosure packet before advertising a unit for rent. This means gathering all existing test results and mitigation records, confirming whether any mitigation system is in place and operational, and preparing the written disclosure document that complies with SB23-206 before a prospective tenant ever signs anything. For property managers overseeing multiple units, establishing a standardized disclosure workflow across the portfolio is far more efficient than handling each unit ad hoc and reduces the risk of a missed disclosure becoming a legal issue. For real estate agents, staying current on the Colorado Division of Real Estate’s Commission-approved forms and ensuring that clients understand both what must be disclosed and when is part of meeting professional obligations under the law. Whether you’re advising a seller or a landlord, the question of is radon mitigation worth it often answers itself once the disclosure obligations and potential transaction consequences are laid out clearly.
Stay Compliant With Professional Radon Testing
The foundation of compliant radon disclosure is accurate information, and the only way to have accurate information is to test. A seller or landlord who knows their property’s radon level, has documentation of a professional test, and can disclose that information completely and confidently is in the best possible position from both a legal and a transactional standpoint. A seller or landlord who is guessing, relying on outdated results, or hoping the buyer’s inspector doesn’t find anything elevated is carrying unnecessary risk into a transaction that can be settled with a simple test.
Better Colorado Radon provides professional radon testing for Colorado homeowners, landlords, and property managers, producing results and documentation that meet state standards and support compliant disclosure under SB23-206 and the Seller’s Property Disclosure requirements. Whether you’re preparing to list a home, onboarding a new tenant, or catching up on a portfolio that hasn’t been systematically tested, our licensed team is ready to help you get the information you need to disclose accurately and confidently.
Book Today to schedule professional radon testing with Better Colorado Radon and go into your next transaction with complete, documented information.
