Landlord Radon Obligations in Colorado
This is a summary, not legal advice. For your situation, consult the statute text and a qualified professional.
Colorado tightened its rental radon rules in 2023, and if you own or rent a home in Larimer or Weld County the details matter more here than in most of the country. Northern Colorado sits inside EPA Radon Zone 1, the highest-potential category, where the predicted average indoor screening level runs above 4.0 pCi/L. That geology is the reason the state wrote radon into landlord-tenant law. This guide walks through what C.R.S. 38-12-803 asks of landlords, what rights it gives tenants, and where each side can read the source text.
This is a summary, not legal advice. For anything specific to your lease, read the statute and talk with a licensed professional.
What the lease disclosure law requires
Senate Bill 23-206 took effect August 7, 2023, and the lease provisions live in C.R.S. 38-12-803. Before a tenant signs a residential lease, the landlord must provide three things in writing.
First, a bold-faced radon warning. Second, any knowledge the landlord has about the property’s radon situation: whether a test was done, the most current records or reports, any concentrations detected, and any mitigation performed. Third, the current CDPHE radon brochure, which the state keeps on its radon and real estate page.
The trigger here is the lease signing itself. The disclosure is not something a landlord hands over after move-in or only when a tenant asks. It comes before the signature. If a home has never been tested, the landlord discloses that too, because “no known information” is itself a disclosure the statute contemplates.
Note the parallel with home sales. The sales version of this law is a different statute, C.R.S. 38-35.7-112, which governs residential real property contracts. Leases and sales are separate sections, so a landlord who also sells property should not assume one disclosure covers the other. Our Colorado radon disclosure law guide covers the sales side in more depth.
The 180-day mitigation window and the tenant’s remedy
The disclosure duty is only half of the statute. The other half deals with what happens after a test comes back high.
A tenant may void the lease and vacate, using the process in C.R.S. 38-12-507, in two situations. One: the landlord failed to provide the required written disclosures. Two: 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.
Two things about that second path are easy to miss. The clock starts when the landlord is notified, not when the tenant first worries about radon. And the 4 pCi/L threshold has to come from a radon measurement professional, which lines up with the EPA action level of 4.0 pCi/L. A store-bought reading a tenant took alone is a useful starting point, but the statute’s remedy hangs on a professional determination. If you are a tenant trying to get a defensible number, our radon testing page explains how we connect you with a licensed measurement professional.
“Reasonable effort to mitigate” is not a blank check to delay. It means the landlord is expected to move toward a fix within that window rather than sit on the result. Landlords planning that work can start with our radon mitigation for rentals page.
The January 1, 2026 carve-out
The remedy changed shape at the start of this year, so the current rule is not what older articles describe.
On or after January 1, 2026, the void-lease remedy does not apply to leases one year or less in duration. In plain terms: as of 2026, a tenant’s right to void and vacate reaches leases longer than one year, and it no longer reaches leases of one year or less. This carve-out is already in effect today.
The written disclosure duty is a different matter. The requirement to hand over the warning, the known radon information, and the CDPHE brochure before signing still applies to residential leases. The carve-out narrows the void-lease remedy; it is not a repeal of the disclosure obligation. Because this is the kind of detail that shifts, both landlords and tenants should read the current text of C.R.S. 38-12-803 and the bill itself, SB23-206, rather than trust a paraphrase.
Non-compliance and the warranty of habitability
Colorado attaches a second consequence to skipping the disclosures. A landlord’s failure to comply with the C.R.S. 38-12-803 disclosure requirements is a breach of the warranty of habitability.
That matters because habitability carries its own set of tenant protections and landlord exposures under Colorado law, separate from the void-lease remedy described above. A landlord could technically avoid a void-lease situation and still face a habitability problem for never providing the written disclosures. The two are not the same lever, and a landlord who treats disclosure as optional paperwork is misreading the risk.
Practical steps for landlords
If you rent out a home in Fort Collins, Loveland, Greeley, or anywhere else in Northern Colorado, a few habits keep you on the right side of the statute.
Test the property so you actually have information to disclose, and keep the records. Testing is the only way to know a specific home’s level, since Zone 1 is a regional prediction, not a guarantee about your address. When a professional test comes back at 4 pCi/L or more, treat the 180-day window as real and line up mitigation early. Keep copies of the bold-faced warning, the disclosure, and the brochure you gave each tenant, dated before the signing.
A standard sub-slab mitigation system in Colorado runs most homes $1,000 to $2,500, with about $1,500 common, according to figures from CDPHE and retail installers. Colorado also runs a low-income program that can cover up to 100 percent of a certified mitigation system, and some Larimer County utility customers may qualify for a rebate, as noted on the larimer.gov radon page. Our radon mitigation cost guide breaks the numbers down further.
Practical steps for tenants
If you rent, you have leverage you may not know about. You are entitled to the written disclosures before you sign, so ask for them if they are missing. If you get a result at or above 4 pCi/L from a measurement professional, notify your landlord in writing and note the date, because that date starts the 180-day clock.
Radon matters here because of health, not paperwork. CDPHE reports that radon is the second leading cause of lung cancer in the United States after smoking, and the leading cause among people who have never smoked. You can read the state’s summary on the CDPHE radon and health page. Understanding a result is easier with our radon test results explained guide.
Where NoCo Radon Pros fits
NoCo Radon Pros is a free matching service, and we hold no Colorado radon license. Colorado licenses radon measurement and mitigation professionals through DORA under House Bill 21-1195, and you can verify any contractor’s credential on the DORA license lookup. We connect landlords and tenants with an independent, state-licensed radon professional; the license and the work belong to that professional, never to us.
For the full statutory picture across sales and leases, see the Colorado radon law guide. When you are ready to line up a test or a mitigation quote, reach out through our contact page, and if you want to understand how a free service stays free, our how we make money page lays it out.
This is a summary, not legal advice.