ADU Laws in New Hampshire (2026)
New Hampshire state ADU law details, key provisions, preemption status, and recent legislative changes for accessory dwelling units.
Law Name
New Hampshire RSA 674:71-73 — Accessory Dwelling Units
Effective Date
2017-09-01
Preempts Local Ordinances
Yes — state law overrides local restrictions
Has State Law
Yes
Key Provisions
Requires all municipalities to allow at least one ADU per single-family dwelling by right or by conditional use permit · Source
ADUs must be permitted on the same lot as the principal dwelling · Source
Municipalities may require that one of the units (primary or ADU) be owner-occupied · Source
Local regulations may set reasonable dimensional standards but may not effectively prohibit ADUs · Source
Municipalities may require a conditional use permit but cannot require a variance or special exception for compliant ADU proposals · Source
Municipalities must define and allow ADUs in their zoning ordinances by 2018 · Source
Legislative History
2017 — RSA 674:71-73 (2016 session, Chapter 6) · Verified June 20, 2026 · Source
Required all New Hampshire municipalities to allow ADUs by right or by conditional use permit. Established minimum standards for ADU size. Enacted via 2016 NH session laws Chapter 6, effective June 1, 2017 — one of the earlier state ADU mandates in New England. · Source
Official Sources
What Does Preemption Mean for Local Cities?
Because New Hampshire law preempts local ordinances, individual cities cannot impose restrictions stricter than the state standard. A city may still have additional administrative requirements, but cannot deny ADU applications that comply with state minimums.
Learn about New Hampshirezoning preemption →Source: New Hampshire RSA 674:71-73 — Accessory Dwelling Units. Last verified April 5, 2026. View source