ADU rules in Hillsborough County, NH β also called accessory dwelling unit regulations or granny flat ordinances β cover setbacks, owner-occupancy, parking, and permit requirements.
Hillsborough County itself does not regulate Accessory Dwelling Units. Under New Hampshire's Home Rule structure (RSA Title LXIV), zoning and ADU regulation is handled by the individual cities and towns - Manchester, Nashua, Merrimack, Hudson, Milford, etc. New Hampshire's statewide ADU enabling law at RSA 674:71-73 requires every municipality with single-family zoning to permit at least one ADU per single-family lot as a matter of right.
New Hampshire counties have very limited regulatory authority. They do not adopt zoning, building, or land-use ordinances - that power is delegated to cities and towns under RSA Title LXIV (Planning and Zoning). Therefore Hillsborough County itself has no ADU rules. The applicable framework is RSA 674:71-73, originally enacted by SB 146 (2016) and significantly strengthened effective July 1, 2025. RSA 674:71 defines an ADU as 'a residential living unit that is located on a lot containing a single-family dwelling that provides independent living facilities,' including provisions for sleeping, eating, cooking, and sanitation. RSA 674:72 requires every municipality to allow one ADU as a matter of right - either attached or detached - per single-family lot. Municipalities may not impose additional restrictions on lot size, setbacks, frontage, aesthetics, or design review beyond what applies to the principal single-family dwelling. The total living space of an ADU may not exceed 950 square feet unless the municipality authorizes more, and municipalities may not cap the size below 750 square feet. RSA 674:73 specifically requires every municipality to permit one detached ADU subject to the same standards. A separate electrical panel and electrical service to the ADU may not be denied. Where a municipality has no ADU ordinance, an ADU is deemed a permitted accessory use as a matter of right. Permits, inspections, and detailed standards are handled by each municipality's planning, zoning, and building departments (Manchester Planning Board, Nashua Building Department, etc.).
Enforcement is municipal, not county. Building or occupying an ADU without the proper municipal building permit, certificate of occupancy, or zoning approval can result in stop-work orders, fines, and required removal under each town's zoning ordinance and the New Hampshire State Building Code (RSA 155-A). Violations of the state ADU statute are appealable through the local zoning board of adjustment and ultimately the New Hampshire Superior Court.
Hillsborough County, NH
Hillsborough County has no county-level noise ordinance. New Hampshire counties have no operational regulatory authority over municipal nuisance matters - ci...
Hillsborough County, NH
Hillsborough County does not regulate fence height. Under New Hampshire's home rule structure (RSA Title LXIV), fence height is set by each municipality's zo...
Hillsborough County, NH
Hillsborough County does not enforce dog leash rules. New Hampshire RSA 466:30-a makes it 'unlawful for any dog to run at large' off the owner's premises, ex...
Hillsborough County, NH
Hillsborough County has no county-level fireworks ordinance. New Hampshire fireworks law is found at RSA 160-C. 'Permissible fireworks' (consumer fireworks e...
Hillsborough County, NH
Hillsborough County does not regulate short-term rental parking. New Hampshire has no statewide STR parking standard. Parking requirements come from each cit...
Hillsborough County, NH
Hillsborough County does not set short-term rental occupancy caps. New Hampshire has no statewide STR occupancy limit. Maximum occupancy is governed by the N...
See how Hillsborough County's adu rules rules stack up against other locations.
Help us keep this page accurate. If you notice an error or outdated information, let us know.