| Max size | 750 sq ftmain house can't drop below 850 sq ft |
|---|---|
| Min size | 350 sq ft |
| Bedrooms | Up to 2 |
| Type | Attached onlydetached banned; state law overrides |
| Parking | 4 spacescombined; state caps ADU add-on at 1 |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Not stated |
| Utility connection | Tie into the existing electrical connection or choose a separate metersame statewide |
The July 2025 state law (RSA 674:71–73) overrides local ordinance language that conflicts with it — even language a town still has posted. Here's what that means in Hudson:
State law now requires Hudson to allow at least one detached ADU by right — including converting a garage or shed. The town's posted ordinance still flatly bans any detached ADU, but that ban predates the 2025 law and is squarely pre-empted.
State law lets the town ask for at most one extra parking space tied to the ADU — and you decide whether it's on your lot or at a legally dedicated off-site spot. Hudson's four-combined-spaces rule and driveway ban go far beyond that and no longer control.
State law says the town can't deny your ADU its own electric meter or utility hookup — a separate connection is your choice, not the town's to withhold. Hudson's ordinance still forbids it, but that prohibition is superseded.
State law puts the choice of a separate vs. shared entrance — and where it goes — in the homeowner's hands. Hudson still requires a shared interior doorway and bans a front-facing ADU entrance, but those requirements no longer control.
Start with your rights under state law: since July 1, 2025, RSA 674:71-73 (as amended by HB 577) guarantees one ADU by right — attached or detached — wherever single-family homes are allowed, protects a separate electrical service for the ADU, puts entrance choice in your hands, and caps any extra parking requirement at one space (on-site or off-site, your choice). Hudson's ADU rules live in Zoning Article XIIIA (§334-73.1 through §334-73.7), originally added in 1995 and last substantively amended March 12, 2019 — well before the current state law — and no later amendment has been identified. What still holds up: an ADU is allowed in any district that permits single-family homes, subject to a building permit and a Zoning Administrator compliance check (no special exception or board hearing referenced); owner-occupancy of either unit is required (a rule towns may lawfully impose, though the town cannot dictate which unit you occupy); max two bedrooms (compliant — state law bars capping at one bedroom, not two); size range of 350-750 sq ft (the 750 cap sits exactly at the state law's floor — a town may cap size but not below 750 sq ft, so Hudson's ceiling is at the tightest legal edge, not a violation); and one ADU per lot (matches the state law's one-ADU guarantee). What state law now overrides: (1) the biggest — Hudson bans detached ADUs entirely (§334-73.3.B); state law requires the town to permit at least one detached ADU, including converting an existing detached garage; (2) Hudson requires FOUR combined off-street parking spaces with no separate driveway (§334-73.3.G) — state law caps what a town can require at ONE extra space, chosen on-site or off-site by the owner; (3) Hudson bans a separate electric meter/utility connection for the ADU (§334-73.3.F) — state law says a town can't deny that; (4) Hudson mandates a shared interior doorway plus bans a front-facing separate entrance (§334-73.3.D, E) — state law puts that choice in the homeowner's hands. Gaps: no numeric ADU setbacks are given in the ADU article (only a cross-reference to 'all setback requirements'), and no exemption is stated for setback-nonconforming conversions of existing structures, which state law otherwise protects. Height, short-term-rental rules, lot coverage, and impact fees are not addressed in the ADU article. One practical note: town staff have verbally indicated that every ADU needs a brand-new surveyor-prepared site plan — a requirement that appears nowhere in the posted ordinance and should be confirmed directly with the town's Inspectional Services department before being treated as fact. Because the posted ordinance is significantly out of date relative to the 2025 state law, confirm current requirements with Inspectional Services before you file anything.
Primary source: eCode360 (General Code) — Article XIIIA added March 14, 1995 (Amdt
Get a free personalized report for your address in Hudson — including where the 2025 law works in your favor.
Get My Free Hudson ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Hudson's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — one ADU is allowed by right in Hudson's single-family districts, and state law now also guarantees you a detached ADU, despite the town's posted ordinance still banning them. Under RSA 674:72 (as amended effective July 1, 2025), one accessory dwelling unit — attached or detached — is allowed by right on single-family lots statewide.
750 sq ft — main house can't drop below 850 sq ft. State law doesn't let any town cap ADU size below 750 sq ft.
Attached only (detached banned; state law overrides). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
4 spaces — combined; state caps ADU add-on at 1. State law caps what any town can require at one additional space, located on- or off-site at the owner's choice.
Required — in either the ADU or the primary home. Where owner-occupancy is required, state law lets the owner choose which unit to live in.