| Max size | 500 sq ftbelow the 750 sq ft state floor |
|---|---|
| Min size | No town minimumbuild as small as code allows |
| Bedrooms | Not stated |
| Type | Attached or detacheddetached = separate accessory building |
| Parking | Not stated |
| Owner-occupancy | Not required |
| 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 Windsor:
Windsor's ordinance still routes every ADU application through a Zoning Board of Adjustment special-exception hearing, where the board can weigh subjective factors like 'effect on adjacent property values.' Since July 2025 that process is no longer enforceable against you — you're entitled to build one ADU by right, with only a building permit, the same as any other addition to your house.
Windsor's 500-square-foot cap is below the legal floor. State law guarantees you at least 750 square feet regardless of what the town's ordinance says, and the town could choose to allow up to 950 sq ft or more.
If you want to convert an existing outbuilding (garage, barn, shed) into an ADU and it's already sitting closer to the property line than today's setback rules allow, Windsor's ordinance doesn't address that scenario — but state law protects it. You are not required to bring a pre-existing nonconforming structure into full setback compliance just because you're converting it into an ADU.
Windsor is New Hampshire's smallest town south of the White Mountains (about 270 residents) and has a single zoning district, governed by its Community Planning Ordinance (adopted 1997, last amended March 9, 2021). That ordinance does address accessory dwelling units, but treats them as a discretionary, not automatic, use: an ADU can only be approved by the Zoning Board of Adjustment as a 'Special Exception,' the same category used for things like earth excavations and light industry. The ordinance also caps any ADU at 500 square feet, requires it to stay 'secondary and incidental' to the main house, limits you to one ADU per residence, ties it to the primary home's existing septic system, and allows shared or separate kitchen facilities, either attached to the house or in a separate building, as long as new construction meets the town's standard 35 ft front / 25 ft side-rear setbacks. It says nothing about owner-occupancy, parking, bedroom counts, or short-term rentals — those are simply not regulated. As of July 1, 2025, New Hampshire's amended ADU law (RSA 674:71-73, via HB 577) overrides two of Windsor's core provisions: (1) the special-exception hearing — you are now entitled to build one ADU by right, without discretionary board approval, in any district (like Windsor's) that allows single-family homes; and (2) the 500-sq-ft cap — the state sets 750 sq ft as the minimum a town must allow, so Windsor's ordinance cannot legally hold you to 500. A third likely gap: the ordinance doesn't carve out an exception for converting an existing nonconforming outbuilding, something state law explicitly protects. Practically, if you're a Windsor homeowner: you do not need to go through the Zoning Board of Adjustment for approval, and you can build well past 500 square feet — up to at least 750, and the town could allow up to 950 or more. Everything else in the ordinance (one ADU per lot, tied to the existing septic, standard setbacks for new construction) is consistent with, or more lenient than, current state law.
Primary source: Town zoning ordinance (PDF) — Community Planning Ordinance originally adopted at Town…
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Get My Free Windsor ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Windsor's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — but Windsor's ordinance still requires a special-exception hearing and caps size at 500 sq ft, both of which the 2025 state law overrides. 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.
500 sq ft — below the 750 sq ft state floor. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or detached (detached = separate accessory building). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
Not required. Where owner-occupancy is required, state law lets the owner choose which unit to live in.