NH RSA 674:72 — Accessory Dwelling Units (HB 577 / Chapter 197 Rewrite) (NH)
Tracked preemption from the New Hampshire overlay bundle.
Overview
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Effective
2025-07-01
Sunset
—
Authority
state
Scope
state:NH
Other New Hampshire preemptions
NH HB 631 / Chapter 201 (2025) — Multifamily / Mixed-Use By Right on Commercial LandNH RSA 674:71 / 674:58–61 — Workforce Housing Reasonable Opportunity MandateNH RSA 483-B — Shoreland Water Quality Protection ActPease ANG (Air National Guard) AICUZ — Federal Airspace and Noise OverlayNH RSA 674:32 — Manufactured Housing Anti-Exclusionary MandateNH RSA 675 — Procedure for Adoption of Zoning, Subdivision, and Site-Plan RegulationsHubbard Brook Experimental Forest — USFS Research Watershed Carve-OutWhite Mountain National Forest — Federal Land Carve-Out (USFS)
Primary-source summary
**Last reviewed**: April 2026
**Activity level**: Medium-to-High — long-standing statutory mandates on ADUs (RSA 674:72) and workforce housing (RSA 674:71) constrain every municipality; legislature has seen repeated 2023-2025 density-preemption attempts (HB 399 / HB 577 / HB 1661) and STR preemption bills (HB 1128). New Hampshire's zoning regime is grounded in the Town Meeting / Select Board governance model, so state mandates interact with a highly decentralized local process.Trigger predicate
When this evaluates true for a parcel, the law's preempted fields take precedence over base zoning.
parcel.base_zone_category ∈ {res_sf, res_mf, res_th, mu}Preempted fields
6 fields on the base district schema are rewritten when the trigger fires.
| Field | Op | Value | Note |
|---|---|---|---|
base_districts[category=res_sf].allowed_uses | add | adu_attached_or_detached_by_right | Every municipality with a zoning ordinance must permit both attached AND detached ADUs by right in any district that allows single-family detached dwellings. Municipalities can no longer restrict to attached-only (the prior 2017 baseline). |
base_districts[category=res_sf].adu_max_size_sf | floor_at | 950 | Municipal cap on ADU size cannot be set below 950 sf |
base_districts[category=res_sf].adu_parking_min | waive | — | No parking minimum beyond the single-family standard; no extra parking spaces may be required for the ADU |
base_districts[category=res_sf].adu_lot_size_min_sf | waive | — | No additional lot-size requirement beyond the underlying single-family minimum |
base_districts[category=res_sf].adu_setbacks | waive | — | No additional setback, frontage, or design restrictions beyond those for single-family |
base_districts[category=res_sf].adu_owner_occupancy | waive | — | No familial-relationship requirement between principal-dwelling and ADU occupants; separate electrical service may not be denied |
Citation
Authority source
NH RSA 674:72 (as rewritten by Chapter 197, Laws of 2025; HB 577 of 2025 session)
§ RSA 674:72
Research notes
Supersedes the 2017 SB-84 attached-only baseline (750 sf floor, owner-occupancy allowed, extra parking allowed, attached-only-permitted-as-municipal-option). 2025-07-01 operative regime: both attached and detached by right, 950 sf floor, no parking add, no familial-relationship rule, no separate-electrical-service denial. Deed-restricted ADUs count toward RSA 674:71 workforce-housing production. Enforcement: private right of action — ZBA (RSA 676:5) → Superior Court (RSA 677:4) or NH Housing Appeals Board (RSA 679). The 2025 HB 577 is a DIFFERENT bill from the 2024-session HB 577 omnibus that died — they share a number but are distinct vehicles.