Montgomery County, MD Accessory Structures: ADU Rules (2026)
ADU rules in Montgomery County, MD, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- License required
- DHCA rental license, § 29-19(b)
- Inspection deadline
- DHCA report within 30 days
- Occupancy cap
- Max 2 adults in ADU
- Units per lot
- One ADU per lot
- Excluded municipalities
- Rockville, Gaithersburg, 5 others
Summary
Montgomery County requires DHCA to license any accessory dwelling unit before it is occupied or rented, unless it was approved as a special exception before May 20, 2013 and still meets those conditions.
Accessory dwelling unit rental license. An owner of a lot or parcel in a zone that permits accessory dwelling units must obtain a license to operate an accessory dwelling unit to live in or to rent if... the Director finds that: (i) the accessory dwelling unit satisfies the standards for an accessory dwelling unit in Section 59.3.3.3 and if needed, a Hearing Examiner granted a waiver under Section 29-26.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-90: Montgomery County Code contains legislation effective through May 7, 2026 | Zoning Updated Effective: April 13, 2026 | COMCOR Regulations effective as of July 1, 2026).
Full Breakdown
Under County Code § 29-19(b), an owner must obtain a DHCA accessory dwelling unit rental license before living in or renting an ADU. The owner posts a Director-issued sign within 5 days of the application, proves the ADU or principal dwelling is the applicant's primary residence, and certifies the ADU is not barred by HOA documents. DHCA inspects the unit and must issue findings within 30 days, then issue or deny the license 30 days after that report unless someone files a timely objection under § 29-26. The unit must also meet the zoning use standards at Ch. 59 § 59.3.3.3.A.2: one ADU per lot, a Zoning Ordinance-compliant setback/coverage footprint, and no more than 2 adult occupants.
Violations & Fines
Operating or renting an ADU without the required license is a Class A violation under § 29-18: up to a $1,000 criminal fine and 6 months jail, or a civil penalty of $500 (initial) / $750 (repeat) under § 1-19.
Frequently Asked Questions
Does this license apply inside Rockville or Gaithersburg?
Can I rent my ADU while my county license is pending?
Sources & Official References
Other rules in Montgomery County
How Montgomery County compares: Easiest Cities to Build an ADU·Compare Montgomery County to another location·View the Maryland accessory structures overview
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