Colorado Radon Disclosure Law: Sales and Leases (SB23-206)

Selling a home

Buyer's right to know: Senate Bill 23-206 added C.R.S. 38-35.7-112, which gives a buyer of residential property the right to know whether it has been tested for elevated radon. The governor approved it on June 5, 2023.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Warning in every contract: Every Colorado contract to sell residential property must carry a bold radon warning that CDPHE strongly recommends buyers test before purchase and mitigate if levels are elevated.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
What sellers disclose: The contract or seller's disclosure must state whether the home was tested, give the most recent radon records and reports, describe any levels found or mitigation done, and say whether a mitigation system is installed.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
CDPHE brochure required: Sellers must also give buyers a paper or electronic copy of CDPHE's most recent brochure on radon in real estate transactions.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Homes covered: The rule covers single family homes, manufactured and mobile homes, condominiums, apartments, townhomes and duplexes, including homes sold by owners, lenders or HUD.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Testing during a sale: CDPHE encourages buyers to have a licensed radon measurement professional test during the inspection period, and to work with the seller on a mitigation system if levels are elevated.Colorado Department of Public Health and Environment, read October 15, 2026

Renting a home

Landlord disclosure law: SB23-206 also added C.R.S. 38-12-803. Before a lease is signed, the landlord must give the tenant a written radon warning, any known radon information and the CDPHE brochure, and the tenant signs to acknowledge it.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Rental rule start date: Colorado landlords have had to disclose radon information when a tenant signs a lease since August 7, 2023.Colorado Department of Public Health and Environment, read October 15, 2026
Tenant may void lease: A tenant may void the lease and move out if the landlord skips the disclosures or makes no reasonable effort to mitigate within 180 days after a radon professional finds 4 pCi/L or more.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Short leases excluded: From January 1, 2026, the right to void a lease over radon does not apply to leases of one year or less.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Habitability link: A landlord who fails to follow the radon disclosure section breaches Colorado's warranty of habitability.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026

Who may test and mitigate

Mandatory licensing date: Since July 1, 2022, anyone who performs radon measurement or radon mitigation in Colorado must meet the state qualifications and hold a license from the director of DORA's Division of Professions and Occupations.Colorado General Assembly (Session Laws 2021, ch. 398, HB21-1195), read October 15, 2026
Two license types: Colorado issues two radon licenses, one for radon measurement professionals and one for radon mitigation professionals. Each requires proof of certification in that discipline from a proficiency program.Colorado General Assembly (Session Laws 2021, ch. 398, HB21-1195), read October 15, 2026
Owner and tenant exemption: The licensing law does not cover a person testing or mitigating a single family home they own and live in. Since 2023 it also exempts a tenant testing the unit they lease.Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026
Measurement standard: A licensed measurement professional must test to the applicable ANSI/AARST radon measurement standard, or another national consensus standard the director approves, and keep a quality control plan.Colorado General Assembly (Session Laws 2021, ch. 398, HB21-1195), read October 15, 2026

EPA's guidance for buyers and sellers

EPA's Home Buyer's and Seller's Guide applies in every state; the state rules above come first where they differ.

Three short-term sale options: For a home sale, EPA's buyer and seller guide accepts any of three short-term testing options to decide whether to fix.U.S. Environmental Protection Agency, read October 15, 2026
Buyer may ask for retest: A buyer may ask for a new test, for example when the seller's test is more than about two years old.U.S. Environmental Protection Agency, read October 15, 2026
Sale test placement: In a sale, the test device goes in the lowest level that could be used regularly, finished or not.U.S. Environmental Protection Agency, read October 15, 2026
Contract: who pays mitigation: EPA suggests buyers consider contract terms for the radon test, including when any mitigation happens and who pays for it.U.S. Environmental Protection Agency, read October 15, 2026

Have a number already? Read your result on EPA's scale. Need a licensed mitigator before closing? Colorado's license list. Hiring an inspector for the sale? Home inspector licensing by state.

Sources

Colorado General Assembly (Session Laws 2023, ch. 356, SB23-206), read October 15, 2026.
Colorado Department of Public Health and Environment, read October 15, 2026.
Colorado General Assembly (Session Laws 2021, ch. 398, HB21-1195), read October 15, 2026.
U.S. Environmental Protection Agency, read October 15, 2026.
U.S. Environmental Protection Agency, read October 15, 2026.

This page explains the rules; it is not legal advice for a particular contract.