Harford County, MD Accessory Structures: ADU Rental Restrictions (2026)

Unlike a typical accessory apartment, Harford County's ADU provision under § 267-28B(8) does not let an owner rent the unit to the general public. Subsection (a) states the purpose plainly: to allow a relative to live in an accessory dwelling unit within a family member's principal dwelling unit. Subsection (c) backs that with an occupancy mandate: the property owner must occupy, as a legal permanent residence, either the principal dwelling unit or the ADU, while the other unit is occupied by the relative. That structure rules out leasing the ADU to a tenant unrelated to the owner, or renting out the main house while leasing the ADU to a stranger.

The restriction has teeth: § 267-28B(8)(h) makes the zoning certificate for the ADU 'null and void' if the property is transferred, conveyed or assigned; if the ADU is no longer occupied by an individual identified under the subsection, meaning the qualifying relative; if the owner no longer occupies either unit; or if any provision of the subsection is violated. A new owner who wants to keep the arrangement going after a sale must obtain a fresh zoning certificate under (g), and the county treats any use outside the relative-occupancy structure, including a market-rate rental, as grounds for voiding the certificate and pursuing enforcement.