Rental Property Radon Testing for Landlords and Property Managers

Who this is for

This service is for landlords, property managers, apartment owners, basement-unit owners, and portfolio operators who need organized radon testing and documentation.

Montgomery County's rental radon law: Section 29-35E

Montgomery County's rental radon requirement is codified at Montgomery County Code § 29-35E, "Radon Testing" — part of Chapter 29, Landlord-Tenant Relations. It was added by Bill 26-22 (lead sponsor Councilmember Rice, co-sponsor Councilmember Katz), enacted November 1, 2022, and took effect July 1, 2023. It expands on the county's older home-sale radon law (Bill 31-15, 2015), which lives in a different part of the code, Chapter 40 § 40-13C — § 29-35E only borrows its definitions of "radon" and "radon test" from that section. Below is a plain-English walkthrough of what § 29-35E actually requires; the county code itself is linked at the bottom of this page.

Which rentals it covers

Under § 29-35E(b), the law applies to all ground-contact or basement units of a residential rental in (1) a single-family home, or (2) a multifamily dwelling building. Two definitional details matter here: § 29-35E(a) defines a "single-family home" as a detached or attached residential building that does not include a unit in a condominium or a cooperative housing corporation, while "multifamily dwelling" carries the broader meaning already set out in § 29-1. In practice, that means the clearest, least ambiguous cases are ground-contact and basement units in single-family rental homes and in multifamily rental buildings — upper-floor units with no ground contact fall outside the law's applicability test. If it's not clear whether a specific unit is covered, Montgomery County's Department of Housing and Community Affairs (DHCA), which administers this law, or your own counsel is the right place to confirm.

Before a new tenant moves in

Under § 29-35E(c), a landlord of a covered unit must have a radon test performed before leasing the unit to a prospective tenant, and that test must have been performed within three years of the lease date. At lease signing, § 29-35E(d) requires the landlord to provide the tenant, and certify in the lease or a lease addendum: (1) a copy of the radon test results showing a concentration below the EPA's action level of 4 pCi/L, (2) confirmation the test was performed less than three years before the lease date, and (3) a copy of the EPA's radon guide for tenants (an electronic link is acceptable; a hard copy must be provided if the tenant asks for one). This initial test is paid for by the landlord.

Can a landlord DIY the required rental radon test?

No. The pre-lease test required by § 29-35E(c) is not satisfied by a landlord placing a DIY test kit themselves. Montgomery County's own Department of Housing and Community Affairs answers this exact question on its landlord guidance page: asked "Can we just order the test kit and do it on our own?", the county's answer is direct — "A landlord must hire a licensed radon professional to conduct the radon test." That applies to the required pre-lease test and to the confirmation retest a landlord must order after a tenant reports an elevated result — a do-it-yourself kit purchased by the landlord does not satisfy this law at any point in the process. (Source: Montgomery County DHCA, Radon Testing and Mitigation for Rental Properties.)

If an existing tenant tests their own unit

The law doesn't just cover new leases. Under § 29-35E(e), an existing tenant may test their own unit, or hire a radon professional to do it, at any point during a tenancy. If that result comes back at or above 4 pCi/L, the tenant must notify the landlord in writing, with a copy of the results, within 14 days of getting the results.

What happens after an elevated result

Once a landlord receives that notice, § 29-35E(f) puts them on the clock twice: within 14 days of notice, the landlord must initiate a follow-up radon test using EPA-recommended testing standards to confirm the hazard; then, within 90 days of that confirmed result, the landlord must mitigate the unit to bring radon below the 4 pCi/L action level and provide the tenant a final copy of professional test results proving it. Under § 29-35E(g), the landlord — not the tenant — pays for the follow-up, confirmation, and any re-testing.

If the landlord's test and the tenant's test disagree

§ 29-35E(h) sets out a specific tiebreaker for disputed results, when a tenant's test is at or above the action level but the landlord's is below it: a for-hire radon professional's test outranks a non-professional test; if both tests were performed by professionals, a long-term test outranks a short-term test; and if the tests are still tied under those two rules, a mutually agreed third-party professional retests the unit under EPA-recommended standards.

Building-wide disclosure and the right to walk away

Two more protections round out the law. Under § 29-35E(i), a landlord who confirms an elevated result must disclose it in writing to every tenant in that residential rental building — not just the tenant whose unit was tested — within 14 days of the confirmed test. And under § 29-35E(j), a tenant has the right to terminate their lease, without losing their security deposit or facing any other financial penalty, if the landlord fails to mitigate within the 90-day window; the tenant gives written notice, and the termination can take effect immediately or on a mutually agreed date that allows time to find alternative housing.

How RADON & CO fits into this timeline

RADON & CO performs the testing side of § 29-35E — the pre-lease test, the 14-day confirmation retest after a tenant reports an elevated result, and the final post-mitigation test that clears a unit below 4 pCi/L — with a digital continuous monitor, a minimum 48-hour closed-house test, and an electronic report you can hand straight to a tenant or keep in a property file. We do not perform mitigation ourselves, by design: if a test comes back elevated, we explain the result clearly and point you to a qualified mitigation contractor, so there's never an incentive on our end to find (or not find) a problem.

Portfolio testing

For multiple rentals, RADON & CO can help create a simple test schedule so units don't drift past the three-year lease-test window, coordinate access across a portfolio, and deliver electronic reports for your property files.

Best fit properties

• Basement units
• Ground-contact units
• Single-family rentals
• Multifamily rental buildings
• Property management portfolios

Official sources

• Montgomery County Code § 29-35E, Radon Testing
• Bill 26-22 as enacted (full text, PDF)
• Montgomery County DHCA: Radon Testing and Mitigation for Rental Properties
• RADON & CO Knowledge Center: full breakdown of the rental radon law

This section is educational and reflects our reading of the enacted bill and Montgomery County's own guidance as of this writing. It is not legal advice — confirm current obligations and deadlines with Montgomery County DHCA or your own counsel.

Frequently asked questions