Haverhill, MA Accessory Structures: ADU Rules (2026)

Section 8.1 of the Haverhill Zoning Ordinance, rewritten by Doc. 119-BB in 2023 and amended again by Doc. 15-B in March 2025, lets homeowners add one accessory dwelling unit per lot. Section 8.1.2 splits ADUs into by-right and special-permit categories: an ADU built completely inside the existing envelope of a principal dwelling of no more than three units is a by-right accessory use needing no special permit, as is an ADU created by adding floor area to a single-family home that still meets all setback and yard requirements. Converting or building a detached accessory structure, such as a garage, barn or carriage house, into an ADU instead requires a special permit from the Board of Appeals, and that detached addition cannot exceed 1,200 square feet or 50% of the existing structure's living space, whichever is less, with no variance available for either limit.

Section 8.1.5 sets the citywide dimensional ceiling: outside the single by-right unit in a single-family zone, no ADU may exceed 1,200 square feet or 40% of the host building's living space, whichever is less, and every ADU must contain at least 350 square feet of habitable space. Every application, whether by-right or by special permit, starts with an application through the Department of Inspectional Services under Section 8.1.3, and all ADUs must independently meet the state building code and hold their own occupancy permit issued by that department. Section 8.1.7 makes the Building Commissioner responsible for enforcement, including cease-and-desist authority over any ADU built or used without the required permit.