As of July 1, 2023, Montgomery County requires radon testing for multifamily (including condominiums) and single-family rental housing as well as disclosure and mitigation of radon hazards above a certain action level.

Montgomery County is among eight counties that have been designated by the U.S. Environmental Protection Agency as having the highest potential indoor radon levels in Maryland. Testing is the only effective way to determine levels of radon exposure in a home.

What is Radon?

Radon is an invisible, radioactive gas created during the natural breakdown of uranium in rocks and soils. It is found in nearly all soils. Radon typically moves up through the ground and into homes and buildings through cracks and other holes in the foundation, although there are other radon sources.

Radon usually does not present a health risk outdoors because it is diluted in the open air. Radon can, however, build up to dangerous levels inside a house.

What areas are at risk for radon?

Montgomery County has high levels of radon in the soil, and therefore, every home in Montgomery County should be tested for radon. 

The U.S. Environmental Protection Agency (EPA) has worked with state and federal geologists to develop maps which predict the potential indoor radon levels for every county in the United States. Those counties with the highest potential are designated as Zone 1; those with the lowest comprise Zone 3. 

Montgomery County has been designated as a Zone 1 area which means there is a predicted average radon level at or above the EPA’s 4.0 pico-Curies per liter (pCi/L) action level. (pCi/L is a measure of the amount of radioactivity in a known quantity of air.)  

What type of units are included?

All ground-contact or basement units of a residential rental in a single-family home or multifamily dwelling unit including condominiums.

Health Effects of Radon Exposure

Breathing air that contains radon can cause lung cancer. In fact, the United States Surgeon General has warned that radon is the second leading cause of lung cancer in the United States today, and is the leading cause of lung cancer in nonsmokers. If you smoke and your home has high radon levels, your risk of lung cancer is especially high.

According to the U.S. Environmental Protection Agency (EPA), radon is estimated to cause about 21,000 lung cancer deaths per year. Detailed information about the health effect of prolonged radon exposure can be found on the EPA’s Radon Health Risks Webpage.

What are landlords’ responsibilities?

The landlord must conduct a radon test before leasing a unit to a prospective tenant having been performed within three years before the date of the lease. The landlord is responsible for the cost of testing.
For New Leases (including Lease Renewals)
At the time of the lease signing, the landlord must provide the tenant and certify in the lease or in an addendum to the lease the following-

• A copy of radon test results indicates any concentration of radon is below the EPA’s recommended action level
• The test was performed less than three years before the date of the lease
• A copy of the EPA’s pamphlet is available through electronic link or by hard copy if requested by the tenant