Harford County, MD Accessory Structures: ADU Rules (2026)
ADU rules in Harford County, MD, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- ADUs per lot
- 1 maximum
- Size range
- 300 to 1,500 sq ft
- Bedroom cap
- 2 bedrooms
- Districts allowed
- AG, RR, R1-R4, RO, VR
- Application requires
- ADU agreement + deed copy
- Certificate voids on
- Sale or vacancy per (h)
Summary
Harford County allows one accessory dwelling unit (ADU) per lot in the AG, RR, R1-R4, RO and VR Districts under § 267-28B(8)(b) of the zoning code, so a relative can live within a family member's home. The ADU must be attached to or located inside the existing house, sized between 300 and 1,500 square feet, and capped at 2 bedrooms.
One ADU is permitted on a single lot in the AG, RR, R1, R2, R3, R4, RO and VR Districts, provided that: ... The ADU shall be physically attached to or located within a single-family detached dwelling unit on the lot. ... The ADU shall be at least 300 square feet in size but shall not exceed the lesser of 1,500 square feet or 50% of the total habitable space of the existing single-family detached dwelling unit. ... The ADU shall not contain more than 2 bedrooms. ... The ADU shall be separated from the single-family detached dwelling unit by means of a wall or a floor, with an interior door between the accessory dwelling unit and the principal single-family detached dwelling unit.
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
' Subsection (b) sets the physical rules: the ADU must be attached to or located within the existing single-family detached house (new additions or renovations must meet all Zoning and Building Code requirements), must be at least 300 square feet but no more than the lesser of 1,500 square feet or 50% of the home's total habitable space, cannot exceed 2 bedrooms, and must be separated from the main house by a wall or floor with an interior door connecting the two, plus its own cooking, living, sanitary and sleeping facilities.
The ADU keeps the same street address as the main house under (d). To apply, the owner submits a signed ADU agreement of understanding and a copy of the property deed with the zoning certificate application under (e); the Department then issues the certificate once those requirements are satisfied, per (f). If the property is later sold, § 267-28B(8)(g) requires the new owner to obtain a fresh zoning certificate before continuing to use the ADU. Having an ADU is not, by itself, grounds for a hardship variance under § 267-11, per (i).
Violations & Fines
Building an ADU larger than 1,500 square feet or 50% of the home's habitable space, adding a third bedroom, or occupying it without a zoning certificate violates § 267-28B(8)(b). The certificate becomes void under § 267-28B(8)(h) if the property is transferred, the ADU is no longer occupied as the section requires, or the owner stops occupying the property; continued use afterward is enforced under § 267-14, with fines up to $500 per day.
Frequently Asked Questions
How big can an accessory dwelling unit be in Harford County?
What do I need to apply for an ADU zoning certificate?
Does selling my house end the ADU's zoning certificate?
Sources & Official References
Other rules in Harford County
How Harford County compares: Easiest Cities to Build an ADU·Compare Harford County to another location·View the Maryland accessory structures overview
See something wrong?
Help us keep this page accurate. If you notice an error or outdated information, let us know.