Harford County, MD Accessory Structures: ADU Owner Occupancy (2026)
Key Facts
- ADU size
- 300 to 1,500 sq ft, max 50% of home
- Bedroom cap
- No more than 2 bedrooms
- Eligible districts
- AG, RR, R1-R4, RO, VR
- Who may occupy
- A relative of the owner
- Application
- Signed ADU agreement plus deed copy
- Certificate voids if
- Sale, vacancy, or non-relative occupant
Summary
Harford County allows one accessory dwelling unit per lot in the AG, RR, R1-R4, RO and VR Districts, but only to house a relative, and the property owner must live in either the main house or the ADU as a legal permanent residence.
(8) Accessory dwelling units (ADU). ... (a) Purpose. The purpose of the accessory dwelling unit is to allow a relative to live in an accessory dwelling unit within a family member's principal dwelling unit. (b) One ADU is permitted on a single lot in the AG, RR, R1, R2, R3, R4, RO and VR Districts, provided that: ... (c) The property owner shall occupy, as his or her legal permanent residence, either the principal single-family detached dwelling unit or the accessory dwelling unit, and the other dwelling unit shall be occupied by the relative. ... (h) The zoning certificate for the ADU shall be deemed null and void if: [1] The property is transferred, conveyed or assigned; or ... [3] The property owner no longer occupies either the primary single-family detached dwelling or the accessory dwelling unit; or [4] A violation of any provision of this subsection.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4988582; v46 updated 2026-06-09; through 06-09-2026).
Full Breakdown
Code of Harford County § 267-28B(8) permits a single ADU on a lot in the AG, RR, R1, R2, R3, R4, RO and VR Districts, built to house a relative of the property owner. The unit must be attached to or located within an existing single-family detached dwelling, measure between 300 and 1,500 square feet and no more than 50% of the principal home's habitable space, hold no more than 2 bedrooms, and be separated from the main house by a wall or floor with a connecting interior door.
It needs its own cooking, sanitary and sleeping facilities and must share the principal dwelling's street address. Before a zoning certificate issues, the owner submits a signed ADU agreement of understanding and a copy of the property deed to the Department of Planning and Zoning. The controlling condition is occupancy: the owner must live in either the principal dwelling or the ADU as a legal permanent residence, with the relative occupying the other unit. If the property changes hands, the new owner needs a fresh zoning certificate to keep the ADU in use.
Under § 267-28B(8)(h), the certificate is automatically null and void if the property is transferred, conveyed or assigned, if the ADU is no longer occupied by a qualifying relative, if the owner stops occupying either unit, or if any provision of the subsection is violated. The code also states that obtaining an ADU certificate is never grounds for, or evidence supporting, a hardship variance under § 267-11.
Violations & Fines
Once the owner-occupancy condition fails, whether through a property sale without a new certificate, the owner moving out of both units, or the ADU going to someone other than a qualifying relative, the zoning certificate is deemed null and void by operation of § 267-28B(8)(h). Continued use of the ADU after voidance is an unpermitted use enforceable by the Department of Planning and Zoning under the county's general zoning enforcement authority, and the owner cannot use the certificate's earlier issuance as evidence supporting a hardship variance under § 267-11.
Frequently Asked Questions
Can I rent Harford County's ADU to a non-relative?
Do I have to live on the property myself?
What happens to the ADU certificate if I sell the house?
How big can a Harford County ADU be?
Sources & Official References
Other rules in Harford County
Compare Harford County to another location·View the Maryland accessory structures overview
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