| Max size | 1,000 sq ftgross living area |
|---|---|
| Min size | 350 sq ftgross living area |
| Bedrooms | Up to 2 |
| Type | Attached onlydetached not clearly allowed |
| Parking | Not statedno ADU parking rule in ordinance |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Not stated in ADU sectionseparate STR ordinance not captured |
| 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 Brookline:
Since July 1, 2025, state law entitles you to build one ADU without any board hearing. Brookline's ordinance (last touched March 2024) still says you must go through a Zoning Board of Adjustment special-exception hearing — but that process is superseded; you're entitled to a by-right permit.
State law gives you an outright right to build a genuinely separate, stand-alone ADU if you prefer. Brookline's ordinance was written around the idea that an ADU has to be tucked inside or attached to your house or an existing outbuilding — but that narrower attachment requirement doesn't survive the state mandate.
State law gives you the choice of entrance location and connection style. Brookline's ordinance still forces an interior connecting door AND bans any exterior ADU entrance on the front of the building — but the town can't dictate either one anymore.
State law resolves this silence in your favor: nonconformity of the existing structure isn't a valid reason to deny the conversion. The ordinance doesn't say you're barred from converting an old, nonconforming garage into an ADU — but it doesn't say you're allowed to, either; under state law, you are.
Start with the state-law baseline: since July 1, 2025, New Hampshire law (RSA 674:71-73, as amended by HB 577) entitles you to one accessory dwelling unit — attached or detached — by right wherever single-family homes are permitted, with no special exception or board hearing, no town-dictated entrance location, and protection for converting existing nonconforming structures. Brookline's ADU ordinance (Zoning §2000.00-2004.00) was last amended March 12, 2024 — before that state law took effect — and has not been updated to match it, so several of its provisions are now overridden. Biggest issue: the ordinance still says you must win a Zoning Board of Adjustment special-exception hearing to add an ADU, when state law now entitles you to one ADU by right, no hearing required. Second: the ordinance requires the ADU be 'within or attached to' the principal house or an existing accessory building, with no clear allowance for building a genuinely free-standing, stand-alone detached ADU — state law guarantees that choice, and the town's narrower requirement doesn't survive it. Third: the ordinance mandates an interior connecting door AND bans any exterior ADU entrance on the front of the building — state law gives homeowners the choice of entrance location and connection style, so those restrictions no longer control. Fourth, more minor: the ordinance is silent on whether an existing, setback-nonconforming accessory structure (like an old garage) can be converted into an ADU — state law says it can, regardless of nonconformity, so that silence resolves in the homeowner's favor. On the plus side, several parts of Brookline's ordinance are already compliant or more generous than the state floor: its 1,000 sq ft size cap exceeds the state's default 950 sq ft ceiling, it allows up to two bedrooms (state law bars a one-bedroom cap), owner-occupancy is required without specifying which unit (owner-occupancy requirements are allowed), and — because Brookline has no general off-street parking requirement for single-family homes anywhere in its ordinance — it cannot and does not require any extra parking space for an ADU. A few details couldn't be confirmed from the ordinance itself — any impact fee, a town-contact point person, and how the town's separate Short Term Rental Ordinance (§2450) interacts with ADUs — so check those directly with the town. See conflicts[] for full citations.
Get a free personalized report for your address in Brookline — including where the 2025 law works in your favor.
Get My Free Brookline ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Brookline's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — and under the 2025 state law you're entitled to one ADU by right, no hearing required. Brookline's ordinance (last updated March 2024) still says a Zoning Board special-exception hearing is required, but state law now overrides that. 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.
1,000 sq ft — gross living area. State law doesn't let any town cap ADU size below 750 sq ft.
Attached only (detached not clearly allowed). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
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.