Carroll County, MD Accessory Structures: ADU Rules (2026)
ADU rules in Carroll County, MD, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Attached ADU max size
- 800 sf or 1/3 of home, greater
- Detached ADU size limit
- None; lot must be subdividable
- Attached ADU bedrooms
- Two bedrooms maximum
- Parking required
- Two extra off-street spaces
- ADUs per lot
- One only, attached or detached
- Occupancy rule
- Owner must occupy main home or ADU
Summary
Carroll County zoning allows one accessory dwelling unit per lot in the Residential Districts, attached or detached, under § 158.075.02(A)(2) and (6). An attached ADU is capped at 800 square feet or one-third of the principal home's floor area, whichever is greater, plus two bedrooms; a detached ADU carries no size cap but needs a subdividable lot.
(2) Attached accessory dwelling units, which are subject to the following: (a) An attached accessory dwelling must have direct access from the outside. (b) Only one attached accessory dwelling is permitted on any principal dwelling unit. (c) The property owner must occupy either the principal dwelling unit or the attached accessory dwelling unit on the property. (d) The maximum size of an attached accessory dwelling shall be 800 square feet of livable floor area or one-third of the total livable floor area of the principal dwelling unit, whichever is greater. (e) The attached accessory dwelling unit shall have no more than two bedrooms. ... (h) Only one accessory dwelling unit (attached or detached) shall be permitted on a lot. ... (6) Detached accessory dwelling units, provided that the lot or parcel is eligible to be subdivided to separate the detached accessory dwelling and which are subject to the following: (a) Only one attached or detached accessory dwelling unit is permitted on any lot or parcel. ... (e) Detached accessory dwelling units shall not be subject to any size limits.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: 2026 S-15: Supplement contains: Local legislation current through July 30, 2026).
Full Breakdown
02(A)(2), an attached accessory dwelling unit must have its own outside entrance, cannot exceed 800 square feet of livable floor area or one-third of the principal dwelling's livable area (whichever is greater), and is limited to two bedrooms. The property owner must live in either the principal unit or the attached ADU, two extra off-street parking spaces are required, and the unit must meet Maryland Department of Health and Mental Hygiene and MDE construction codes. A detached ADU under (A)(6) has no size limit at all, but the lot must be eligible for subdivision to separate the two dwellings, the owner must occupy one of the two units, two off-street parking spaces are required, and the same state construction and health codes apply.
Regardless of type, (A)(2)(h) and (A)(6)(a) both cap a single lot at one accessory dwelling unit total, so a property cannot combine an attached and a detached ADU. The Department of Land Use, Planning, and Development administers zoning approvals for these uses, and the rules were adopted by Ord. 2022-03, passed December 16, 2021, and later amended by Ord. 2022-20 and Ord. 2024-10.
Violations & Fines
ADUs are regulated under the county's zoning chapter, so an unpermitted or oversized unit is a zoning violation under § 158.999: up to $1,000 for the underlying violation, plus a civil fine schedule starting at $50 for a first offense, $100 for a second, $200 for a third, and $500 for each later offense, with every day a violation continues counted as a separate offense. Citations are payable within 15 days to the County Commissioners' Collections Office, doubling if unpaid.
Frequently Asked Questions
Can I build both an attached and a detached ADU on the same Carroll County lot?
Does a detached ADU in Carroll County have a size limit?
Who has to live on the property with a Carroll County ADU?
Sources & Official References
Other rules in Carroll County
How Carroll County compares: Easiest Cities to Build an ADU·Compare Carroll County to another location·View the Maryland accessory structures overview
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