Radon Testing for Rentals

Colorado SB23-206 extends radon disclosure obligations to residential leases — not just sales. That's a change most landlords and tenants haven't fully internalized yet. This page walks through what landlords must disclose, what tenants can do if they're concerned, and where mitigation responsibility lands.

This is general information, not legal advice. For specific situations, especially landlord-tenant disputes, consult a Colorado real estate attorney.

Since August 7, 2023, residential landlords in Colorado must:^[1]

• Disclose any known prior radon test results for the property in the lease or as a pre-lease disclosure.
• Disclose any radon mitigation work that has been performed.
• Provide the CDPHE radon brochure to the tenant.

The law applies to landlords of any residential property — single-family rentals, condos, apartment units, and multi-family buildings. As with home sales, the law requires disclosure of what is known; it does not require testing or mitigation.

SB23-206 stops short of imposing a duty to test or mitigate. Specifically:

• Landlords are not required to test rental properties for radon before listing.
• Landlords are not required to mitigate even if a test shows elevated levels.
• Existing leases (signed before August 7, 2023) are not retroactively affected by the disclosure rule.

However: the practical reality of disclosure means landlords who know about elevated radon and don't address it may face friction from prospective tenants, lower rental rates, or attorney-led tenant inquiries if a health issue later arises. Many Colorado landlords have started testing rentals proactively because the disclosure burden makes "I didn't know" a less defensible position.

Before signing a lease

Read the disclosure. If the landlord checked "yes" to a prior radon test, ask for the actual test result. If they checked "yes" to mitigation, ask for the system documentation and post-mitigation test result. If they checked "no known test," that's the standard answer — and you can decide whether to test the unit yourself.

During tenancy

Tenants have the right to test their own unit at any time. A short-term DIY kit ($15–$40) is the easiest path; placement follows the standard EPA guidance (where to place a test →). If you find elevated levels:

1. Document the result in writing to the landlord, ideally with a copy of the lab report.
2. Reference the CDPHE radon brochure (which they should have provided at lease signing).
3. Request mitigation in writing. The landlord is not legally obligated to mitigate, but many will — particularly if you've signed a long-term lease.
4. If the landlord refuses, your options depend on lease terms. Consult a Colorado tenant rights attorney for specifics.

Multi-unit buildings

If you live in an apartment, radon levels can vary by unit. Ground-floor and basement units typically have higher levels than upper-floor units, but radon can rise through buildings via shared shafts and stairwells. A test in your own unit is the only definitive answer.

For Colorado landlords, treating radon testing as a standard pre-lease item — like a smoke detector check — is increasingly common:

• The disclosure requirement now exists. "I didn't test, so I had nothing to disclose" is a less defensible position than "I tested and disclosed the result."
• Test cost is modest. A short-term test costs $15–$40; a long-term test costs $30–$60. Either is well under one month's rent.
• If the test result is high, you're not legally required to mitigate — but you are required to disclose. Most Colorado landlords in this position mitigate because the disclosure makes the unit harder to rent without mitigation.
• If you do mitigate, the system documentation and post-mit test result transfer with the property and become part of every future disclosure.

Mitigation costs are the same for rentals as for owner-occupied homes — the system is the same. Colorado Springs cost bands:

• Basic basement (single-family rental): $900–$1,900
• Finished basement: $1,400–$2,800
• Crawlspace: $1,800–$4,000
• Multi-zone or duplex: $2,200–$4,800

For multi-family buildings (apartments, condos), commercial AARST standards apply (SGM-MFLB-2023), and costs scale with the building's size. Full cost breakdown →