Montgomery County Rental Property Radon Testing Requirements

Direct answer

Yes. Since July 1, 2023, Montgomery County Code § 29-35E, "Radon Testing" (Chapter 29, Landlord-Tenant Relations), requires landlords to test all ground-contact or basement rental units in a single-family home or multifamily dwelling building for radon before leasing to a new tenant, disclose the results, and mitigate within 90 days if a confirmed test comes back at or above the EPA's action level of 4 pCi/L. The law was added by Bill 26-22 (lead sponsor Councilmember Rice, co-sponsor Councilmember Katz; enacted November 1, 2022) and builds on the county's earlier home-sale radon law, Bill 31-15 (2015), which is codified separately at § 40-13C — § 29-35E only borrows its definitions of "radon" and "radon test" from that section, so it's a common but incorrect citation to point to 40-13C for the rental requirement itself.

What properties are covered

§ 29-35E(b) applies the law to all ground-contact or basement units of a residential rental in (1) a single-family home, or (2) a multifamily dwelling building. § 29-35E(a) specifically defines "single-family home" as a detached or attached residential building that does not include a unit in a condominium or cooperative housing corporation; "multifamily dwelling" uses the broader definition already in § 29-1. Units with no ground contact and no basement location are outside the law's applicability test as written.

Before a new lease: the pre-lease test

§ 29-35E(c) requires the landlord of a covered unit to have a radon test performed before leasing to a prospective tenant, with results dated within three years of the lease. § 29-35E(d) then requires the landlord, at lease signing, to certify in the lease or an addendum and provide the tenant: (1) the test results showing radon below the EPA's 4 pCi/L action level, (2) confirmation the test is within the three-year window, and (3) a copy of the EPA's radon guide for tenants (electronic link is acceptable unless the tenant requests a hard copy). The landlord pays for this test.

Can a landlord DIY the required test?

No. Montgomery County's Department of Housing and Community Affairs addresses this directly in its own landlord FAQ. Asked "Can we just order the test kit and do it on our own?", DHCA answers directly: "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 elevated results — a DIY kit does not satisfy the law at any point in the process. (Source: Montgomery County DHCA.)

During a tenancy: if a tenant tests on their own

The law isn't limited to move-in. § 29-35E(e) allows an existing tenant to test their own unit, or hire a radon professional, at any point. If that result is at or above 4 pCi/L, the tenant must notify the landlord in writing, with the results, within 14 days.

The mitigation clock: 14 days, then 90 days

Once notified, § 29-35E(f) requires the landlord to initiate a confirmation retest, using EPA-recommended testing standards, within 14 days of notice. If that retest confirms the hazard, the landlord then has 90 days from the confirmed result to (A) mitigate the unit below the 4 pCi/L action level and (B) give the tenant a final professional test report proving it. § 29-35E(g) puts the cost of the follow-up, confirmation, and any re-testing on the landlord, not the tenant.

Disputed results

§ 29-35E(h) sets a tiebreaker 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 result outranks a non-professional's; between two professional results, a long-term test outranks a short-term test; and if still unresolved, a mutually agreed third-party professional retests under EPA-recommended standards.

Building-wide disclosure and lease termination

§ 29-35E(i) requires the landlord to disclose a confirmed elevated result, in writing, to every tenant in that rental building — not only the tenant whose unit was tested — within 14 days of confirmation. § 29-35E(j) gives a tenant the right to terminate their lease without losing their security deposit or facing any other financial penalty if the landlord misses the 90-day mitigation deadline, with the termination effective immediately or on a mutually agreed date.

How RADON & CO helps

RADON & CO can perform the pre-lease test, the 14-day confirmation retest after a tenant reports an elevated result, and the final clearance test after mitigation — all with a digital continuous monitor, a minimum 48-hour closed-house test, and an electronic report for your lease file or tenant disclosure. We do not perform mitigation ourselves; if a result is elevated, we explain it and point you to a qualified mitigation contractor.

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
• EPA: Health Risk of Radon

Disclaimer: This page is educational and reflects our reading of the enacted bill and county guidance as of this writing. It does not replace legal, lender, HUD program, or environmental consultant guidance — confirm current obligations and deadlines with Montgomery County DHCA or your own counsel.

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