| Max size | 980 sq ft1,200 inside an existing structure |
|---|---|
| Min size | No town minimumbuild as small as code allows |
| Bedrooms | Not statedNo bedroom cap in the ordinance |
| Type | Attached + detachedBy right; no hearing |
| Parking | 1 spaceyour choice on/off-site |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Not statedNo ADU-specific rule adopted |
| 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 Nashua:
If you want to convert an existing garage that's already too close to your property line into an ADU, Nashua's ordinance doesn't say one way or the other — but state law says you're entitled to do it anyway, nonconforming setbacks and all. The city's own nonconformity rules (Article XII) may or may not already cover this; a homeowner should not assume the omission means 'no.'
Nashua makes you record a deed covenant and pay a filing fee before you can even get a building permit for your ADU — something an ordinary single-family homeowner never has to do. Whether that's legal under the new state law hasn't been tested; it's a question for a land-use attorney, not a bright line either way.
State law says the off-site parking choice is yours, period. Nashua's ordinance technically agrees you can go off-site, but inserts a city sign-off on whether your lease or agreement is 'acceptable.' That extra gatekeeping step is a gray area — it could be read as a reasonable paperwork check, or as the city retaining more control than the statute allows.
Nashua's Land Use Code (§190-32, City of Nashua, NH — Chapter 190, Part 2, Article VI) treats an accessory dwelling unit as a permitted accessory use tied to any single-family detached dwelling — no special exception, conditional use permit, or Planning Board/ZBA hearing is required. The city amended this section on December 23, 2025 (Ord. No. O-25-076) specifically to bring itself into compliance with New Hampshire's HB 577, which took effect July 1, 2025.
What you get: one ADU per single-family lot, attached OR detached (the code's own definition of 'accessory dwelling unit' — 'contained within, attached to, or detached from a single-family dwelling' — confirms detached units are fully allowed, not just tolerated). The unit can be up to 980 square feet, or up to 1,200 square feet if you're converting the interior of an existing structure without expanding its footprint — both numbers exceed the state law's 950-square-foot default cap, which the state statute allows a town to do. There's no minimum size and no bedroom cap written into the ordinance. You (the owner) must live in either the main house or the ADU — the city doesn't get to tell you which one. You'll need one extra parking space, which by ordinance can be located on-site or off-site (matching the state law's owner's-discretion rule), and an attached ADU's entrance can be independent or shared through the main house — your choice, which is exactly what state law requires.
What the city adds on top of the state floor: before you get a building permit, you must record a covenant at the Hillsborough County Registry of Deeds disclosing that the property has an ADU, and pay the filing fee. You also can't sell the ADU as a separate condo unit, and you can't put an ADU on a townhouse-style attached single-family home — both of those restrictions are explicitly allowed under state law, so they're not something to fight. Where the ordinance goes quiet rather than conflicting outright: it doesn't spell out that converting an already-nonconforming detached garage into an ADU is protected from current setback rules (state law says it is), and the off-site parking option requires the city's 'Administrative Officer' to approve your lease or instrument, which arguably adds a layer of city discretion the state statute didn't call for. Neither of those is a slam-dunk 'town loses' — they're areas where a land-use attorney's read matters before you rely on them.
Primary source: eCode360 (General Code) — §190-32 amended 8-8-2017 (Ord
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Get My Free Nashua ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Nashua's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Nashua allows one accessory dwelling unit (attached or detached) by right on any single-family lot, and the city rewrote its ordinance in December 2025 specifically to comply with the new state law. 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.
980 sq ft — 1,200 inside an existing structure. State law doesn't let any town cap ADU size below 750 sq ft.
Attached + detached (By right; no hearing). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 space — your choice on/off-site. 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.