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Accessory Dwelling Units (ADUs)

ADUs in Montgomery County 

An Accessory Dwelling Unit as defined in Montgomery County code is a second dwelling unit that is subordinate to the principal dwelling. An ADU can be an addition or basement (attached) or separate structure on the same lot (detached). 

Building an ADU in Montgomery County, MD is mostly a by-right process facilitated through Montgomery County’s Department of Housing and Community Affairs and Department of Permitting Services. 

Visit DHCA’s website to learn about how to apply to for a Accessory Dwelling Unit Class 3 License. 

Changes made in 2019 through ZTA 19-01 

ZTA 19-01, introduced in January 2019 and approved in July 2019 revised the limited use provisions for attached and detached Accessory Dwelling Units. 

Changes that were made in ZTA 19-01 include:  


Frequently asked questions

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