Nashua, NH Accessory Structures: ADU Rules (2026)
ADU rules in Nashua, NH, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- 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
Summary
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.
The owner of the property shall provide the City of Nashua with a covenant for filing with the Hillsborough County registry of deeds, along with the appropriate filing fees. The covenant shall read substantially as follows: "_____of _____ covenants and agrees that the property located at _____ contains an accessory dwelling as defined by the City of Nashua Land Use Code (§ 190-264 of Article XLII). The continued use of the accessory dwelling unit is conditioned upon compliance with all current and subsequently adopted ordinances and statutes applicable to the property." The granting of a building permit for the accessory dwelling unit shall be contingent upon receipt of the covenant and fees.
(7) One additional off-street parking space is required above the minimum standard for a single-family house, either on-site or at an off-site location and legally dedicated via a lease agreement or other instrument deemed acceptable by the Administrative Officer.
(8) Attached accessory dwelling units shall either have an independent means of ingress and egress or ingress and egress through a common space shared with the principal dwelling.
(9) The single-family dwelling and the accessory dwelling unit shall not be separated in ownership (including by condominium ownership).
(10)
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4805762; v29 updated 2026-02-10; through 02-10-2026).
Full Breakdown
Nashua's zoning code allows one accessory dwelling unit per single-family lot, capped at 980 square feet, or 1,200 square feet if built inside an existing structure's footprint without expanding it. The property owner must occupy the primary or accessory unit as a principal residence, and the ADU cannot be sold separately from the main house. One extra off-street parking space is required beyond the standard minimum. Before the City issues a building permit, the owner must file a covenant with the Hillsborough County Registry of Deeds committing the property to ADU compliance, plus applicable filing fees, under Nashua Revised Ordinances § 190-32.
Violations & Fines
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.
Frequently Asked Questions
How big can a Nashua ADU be?
Do I need a permit to build an ADU in Nashua?
Sources & Official References
Other rules in Nashua
How Nashua compares: Easiest Cities to Build an ADU·Compare Nashua to another location·View the New Hampshire accessory structures overview
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ADU Rules in Nearby Cities
How other cities in this county handle adu rules.