Nashua's Accessory Structures: The Rules That Matter

Every city handles accessory structures a little differently. In Nashua, New Hampshire, there are 3 distinct rules that residents and property owners should be aware of. Some are stricter than what neighboring cities enforce, and others are more relaxed. Here is what you need to know.

ADU Rules

Nashua accessory dwelling units are capped at 980 square feet (1,200 if built within an existing footprint), require owner-occupancy, extra parking, and a covenant filed with the Hillsborough County Registry of Deeds before a building permit issues.

Key details: Max size: 980 sq ft (1,200 in existing footprint). Units per lot: One ADU per single-family lot. Owner occupancy: Owner must occupy primary or ADU. Parking: One extra off-street space required. Permit prerequisite: Covenant filed with County Registry of Deeds.

The City won't issue a building permit until the covenant is filed and fees are paid; continued ADU use is conditioned on ongoing compliance, and noncompliant units are subject to standard zoning enforcement.

ADU Owner Occupancy

Nashua's accessory dwelling unit ordinance requires the property owner to live in either the primary house or the ADU as their principal residence, backed by a recorded covenant filed with the county registry of deeds.

Key details: Owner-occupancy: Owner must live in primary or ADU. Covenant: Filed with Hillsborough County registry of deeds. Permit hold: Building permit contingent on covenant filing. Housing type: Single-family detached dwellings only. Ownership: Primary and ADU can't be separately owned.

Continued use of the ADU is conditioned on compliance with all current and subsequently adopted ordinances and statutes; breaching the recorded owner-occupancy covenant can jeopardize the ADU's authorized status under § 190-32(B)(6).

Shed & Carport Rules

Nashua charges a flat $30 minimum permit fee for residential sheds under 200 square feet, billed as miscellaneous equipment rather than per-square-foot new construction; the city requires a building permit before any work begins.

Key details: Permit required: Yes, regardless of shed size. Fee under 200 sq ft: $30 flat residential minimum fee. Fee 200+ sq ft: $0.18 per square foot. Min front setback: 20 feet. Late-start surcharge: 100% of fee, capped $275.

Starting construction without a permit adds a 100% fee surcharge, capped at $275 for residential work, and Building Code violations are enforced under NRO Chapter 74 and RSA 676:15-17-b.

The Bottom Line

Nashua's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Nashua is broadly strict or permissive.

Keep in mind that Nashua can amend these rules at any council meeting. For the most current version of any rule mentioned here, check the specific ordinance page, where we track updates as they happen.