New Hampshire Statewide Rule
New Hampshire ADU Statute Mandates Local Authorization
Key Facts
- Statute
- RSA 674:71 to 674:73
- One ADU
- Allowed as of right (2025)
- Special exception
- No longer permitted
- Minimum size floor
- 750 sq ft
- Default maximum
- 950 sq ft
Summary
New Hampshire RSA 674:71 to 674:73 requires every municipality that allows single-family homes to permit at least one accessory dwelling unit. A 2025 amendment makes one ADU allowed as of right, so towns may no longer require a special exception or conditional use permit.
A municipality that adopts a zoning ordinance pursuant to the authority granted in this chapter shall allow accessory dwelling units in all zoning districts that permit single-family dwellings. One accessory dwelling unit, which may be either attached or detached, shall be allowed as a matter of right. The municipality shall allow one accessory dwelling unit without additional requirements for lot size, except as described by this section, setbacks, aesthetic requirements, design review requirements, frontage, space limitations, or other controls beyond what would be required for a single-family dwelling without an accessory dwelling unit.
Full Breakdown
Enacted in 2016 and strengthened by a 2025 amendment, RSA 674:71 to 674:73 requires municipalities whose zoning permits single-family detached homes to allow at least one attached or detached accessory dwelling unit. As of the 2025 amendment, one ADU must be allowed as a matter of right; a municipality may not require a conditional use permit or special exception. Towns may not limit an ADU to less than 750 square feet, and the default maximum is 950 square feet unless the town allows larger. Municipalities may require owner-occupancy of one unit (but not specify which) and may not require a familial relationship between occupants. Outright bans are prohibited.
Violations & Penalties
Local ordinances inconsistent with RSA 674:71 to 674:73 are unenforceable; aggrieved property owners may appeal denials to the zoning board of adjustment and superior court.
Frequently Asked Questions
Can my New Hampshire town ban accessory dwelling units?
How big can a New Hampshire ADU be?
Sources
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