| Max size | 800 sq ft"in-law" type capped at 400 sq ft |
|---|---|
| Min size | No town minimumbuild as small as code allows |
| Bedrooms | Up to 2 |
| Type | Attached or detacheddetached needs a special exception |
| Parking | 1 spaceoff-site option not mentioned |
| 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 Rochester:
Since July 1, 2025, state law entitles you to build a detached ADU by right — no hearing required — the same as an attached one. Rochester's ordinance still forces you through a Zoning Board of Adjustment special-exception hearing to build a detached ADU (e.g., converting a garage into an apartment, or a standalone cottage), but state law now overrides this. It is Rochester's biggest and clearest conflict with the new law.
If Rochester's R1 district really does require a special-exception hearing just to add ANY accessory apartment (attached or not), that would conflict with the state law's by-right guarantee in every single-family district. The use table's reading is uncertain enough that this needs to be manually confirmed against the live eCode360 table before being stated as fact.
Rochester can require your detached ADU to architecturally match your house only to the same degree it would require of any other structure on your property — whether the 'similar in architectural style' clause crosses into a stricter design-review standard is an attorney-level judgment call.
This clause only requires that a connecting interior door exist when the ADU is part of the main house — it doesn't explicitly forbid the ADU from ALSO having its own separate exterior entrance. Whether requiring the interior door at all crosses into dictating the homeowner's access choice is ambiguous and should be attorney-reviewed rather than treated as a clear violation.
Rochester can require one extra parking space (that part is compliant), but the ordinance doesn't say you're allowed to put it off-site — state law gives you that choice regardless of what the local text says.
Rochester's posted ADU rules predate the 2025 state law. Unless the City has since updated §275-23.2, every conflict above is currently live and unresolved — state law controls wherever the two differ, and the whole ordinance section is overdue for a rewrite to match the new state floor.
Start with what state law guarantees, because it overrides the city's text wherever the two conflict: since July 1, 2025, RSA 674:71-73 (as amended by HB 577) entitles homeowners to one ADU — attached OR detached — by right in every district that allows single-family homes, with no special-exception hearing, a size cap no lower than 750 sq ft, and at most one required additional parking space with the owner's choice of on-site or off-site placement. Rochester's zoning code (§275-23.2 'Accessory apartment', last amended 3-5-2019) allows an accessory apartment of up to 800 sq ft (two bedrooms max), plus a more limited 400 sq ft 'in-law apartment' option with no separate entrance. The owner must occupy one of the two units (a requirement state law permits), only one accessory apartment is allowed per lot, and one parking space is required. Where Rochester's posted rules fall short of the state floor: (1) the ordinance still requires a Zoning Board of Adjustment special-exception hearing for any DETACHED accessory apartment — state law now entitles homeowners to build a detached ADU by right, no hearing needed; (2) the city's use table (Table 18-A) may still require special-exception approval for the accessory-apartment use itself in at least one residential district — this needs verification against the city's current eCode360 table before being treated as settled; (3) a 'similar in architectural style' requirement for detached units could be read as a stricter design standard than the state now allows; (4) a mandatory interior connecting door, while not an explicit ban on a separate entrance, sits close to the line the state drew around homeowner choice of ingress and egress; (5) the parking clause doesn't mention the homeowner's state-law right to place the required space off-site. Because Rochester's ADU section predates the 2025 state law, confirm current practice with the Building Department before accepting any of the stricter local requirements at face value — the state floor controls wherever the two differ.
Primary source: eCode360 (General Code) — §275-23.2 / Table 18-A amended 4-4-2017…
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Get My Free Rochester ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Rochester's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Rochester allows an accessory apartment up to 800 sq ft by right when attached, and since July 2025 state law guarantees a by-right path for DETACHED ADUs too, overriding the city's special-exception requirement. 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.
800 sq ft — "in-law" type capped at 400 sq ft. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or detached (detached needs a special exception). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 space — off-site option not mentioned. 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.