| Max size | 900 sq ftgross floor area |
|---|---|
| Min size | No town minimumbuild as small as code allows |
| Bedrooms | Not statedno bedroom cap in ordinance |
| Type | Attached onlydetached barred; state law overrides |
| Parking | Adequate off-street parkingno number of spaces given |
| 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 Center Harbor:
As of July 1, 2025, state law entitles you to build a DETACHED ADU — including converting a detached garage. Center Harbor's ordinance and its own staff still say an ADU must be attached, but state law overrides that restriction.
State law says you can build the ADU and a brand-new principal home together in one project. The town's ordinance still reads as if you must already own a house before adding an ADU, but state law overrides that.
State law's nonconforming-lot protection means an undersized lot shouldn't disqualify an otherwise-legal ADU conversion. Center Harbor's ordinance as written could still block your ADU on lot size alone — common on older, in-town lots — but state law overrides that basis.
State law gives the homeowner — not the town — the choice of entrance for an ADU. The town's rule still forces a shared interior door between the two units, but state law overrides it.
State law lets a town require SOME owner-occupancy, but it can't dictate which unit the owner lives in. Center Harbor's phrasing assumes the owner lives in the main house — whether that specific phrasing crosses the line is a close call worth an attorney's read.
Under state law (RSA 674:71-73, as amended by HB 577 effective July 1, 2025), every Center Harbor homeowner in a district that allows single-family homes is entitled to one accessory dwelling unit by right — attached OR detached — and that state entitlement overrides any conflicting town rule. Center Harbor's own ordinance already treats an ADU as a permitted use subject to a checklist of 10 conditions in Zoning Ordinance §5:9:2, not a Special Exception requiring a ZBA hearing, so on the by-right question the town already meets the state's bar. But the substance of §5:9:2 has not changed since March 2018, and it shows: the ordinance's definition (§2:2:20) confines an ADU to a unit 'within or attached to' a single-family dwelling, and §5:9:2 requires it be added to 'an existing owner-occupied structure' — meaning no detached-garage conversions, no stand-alone units, and (as written) no building the ADU alongside a brand-new house. Town staff have confirmed the attached-only reading. State law now overrides all of that: you are entitled to a DETACHED ADU, and to build the ADU concurrently with new construction, regardless of what the town's ordinance says. Other places state law prevails: an ADU-specific minimum-lot-size condition (tied to the district's base lot-size table, 10,000-40,000+ sq ft) could block a conversion on an undersized in-town lot, but state law's nonconforming-lot protection overrides it; and a mandatory interior connecting door removes the homeowner's state-guaranteed choice of entrance, so state law overrides that too. Owner-occupancy is different: state law does let a town require owner-occupancy — it just can't dictate which unit the owner occupies. Center Harbor's language assumes the owner lives in the main house, a close call worth an attorney's read. On the plus side, the town's 900 sq ft size cap sits comfortably above the 750 sq ft floor state law sets for any size cap, there's no bedroom cap, no familial-relationship requirement, and only one ADU per lot with a reasonable bar on townhouse/condo/manufactured-home conversions — all compliant. Parking is the one open item: the ADU section only requires 'adequate off-street parking' with no number given, and the town's general parking standard (Appendix B of the ordinance) could not be confirmed. Under state law the town may require at most one additional space for the ADU, with the on-site vs. off-site choice belonging to the owner — treat the town-specific parking detail as pending verification.
Get a free personalized report for your address in Center Harbor — including where the 2025 law works in your favor.
Get My Free Center Harbor ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Center Harbor's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — and under state law effective July 1, 2025, Center Harbor homeowners are entitled to one ADU by right, attached OR detached. The town's posted ordinance still only recognizes an ATTACHED unit inside or joined to an existing owner-occupied home, but state law overrides that limit. 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.
900 sq ft — gross floor area. State law doesn't let any town cap ADU size below 750 sq ft.
Attached only (detached barred; state law overrides). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
Adequate off-street parking — no number of spaces given. 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.