Blog: 🏡Homeowners: Have You Considered an Accessory Dwelling Unit?

by Tony Byrne, Steering Committee Chair

Accessory Dwelling Units (“ADUs”) have become a hot topic nationally. In different locales ADUs go by different names—tiny homes, granny flats, casitas, basement apartments, and so on—but the idea is the same: a new, separate home on an existing property. 

ADUs can be detached (separate structure from house), attached (addition to house), or interior (i.e. conversion of an existing space within a house, like a basement).

New detached ADU in Bethesda. Photo courtesy of Eric Saul.

The past decade has seen a dramatic rise in legalization of ADUs around the country. ADUs now account for 20% of new unit construction in California and 9% of new permits in Maine just a year after getting approval there! 

Maryland passed a bill in 2025, supported by Montgomery for All and CSG, mandating that each county adopt policies allowing ADUs in all zones that also allow single-family zoning—a major win that will make it possible to build ADUs in far more places across the state. 

Montgomery County has for decades allowed ADUs, albeit under a nearly prohibitive array of limitations. ADUs were not effectively legalized for many homeowners in Montgomery County until after a major fight resulting in significant reforms in 2019 (many of you helped win this…thanks!).  

The County is currently working to loosen restrictions further. The Council will hold a hearing on June 9 on a new set of reforms to align MoCo’s policy with state law, which will expand the zones where ADUs are allowed, modify setback requirements, and more.

Such changes are welcome, as MoCo has not yet adopted ADUs with the same alacrity as other places like Maine and California. The county’s new permitting dashboard suggests that ADUs comprise only 1.2% of all permitted units since 2019.

Yet there’s a great case to be made for building an ADU. Not only do they help us address climate change and our pervasive housing crisis by allowing more affordable homes to be built in existing communities, as a practical matter an ADU can convert your valuable property into rental income, support your extended family, or enable you to age in place.  

Check out the Planning Department’s comprehensive ADU site for more information. AARP also publishes an excellent guide to ADUs.

Photo credit: Eric Saul (used with permission)