| Max size | 950 sq ftconfirmed with the town |
|---|---|
| Min size | No town minimum750 sq ft floor protects you |
| Bedrooms | Up to 2confirmed with the town |
| Type | Attached + detachedBy right, building permit only |
| Parking | 1 Spot for ADU on site or off-streetconfirmed with the town |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Banned in R districtsCitywide use table, not an ADU rule |
| 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 Manchester:
Manchester says the setback/lot-coverage break for converting an existing building into an ADU only applies if that building was already standing before July 1, 2025. State law doesn't include that date cutoff — it protects the conversion of any existing structure, regardless of when it was built. If your garage or shed was built after July 2025 and you later convert it, whether you still qualify for the setback break is a legal gray area worth raising with the Planning Department or an attorney.
Manchester requires your detached backyard ADU to meet a specific window-coverage percentage and have a pitched roof — standards the ordinance does not impose on the main house itself. State law only lets a town hold an ADU to the same look-and-feel rules as an ordinary house, not stricter ones. This detached-ADU-only design requirement appears to cross that line.
Manchester doesn't just require you to live in one of the two units — it permanently encumbers your property's deed to guarantee it, with no stated expiration. State law lets the city require owner-occupancy, but doesn't say it can permanently restrict your title to do it. This is a real, practical cost (it can complicate refinancing and resale) worth understanding, and possibly negotiating the wording of, before you record it.
CONFIRMED WITH THE TOWN (July 21, 2026) — ADUs allowed: 1; maximum size 950 sq ft; up to 2 bedrooms; impact fees: $459 for dwellings with fewer then 2 bedrooms, under 900 SqFt. $1530 for anything greater. Fire impact fee $190; parking: 1 Spot for ADU on site or off-street; detached-unit distance rule: No; setbacks: Most common zone is R-1B (Single Family). Setbacks here are 20' front, rear and side (total of both sides).. Town contact: Jim Tierney - Zoning Review Officer I - 603.792.6741.
An ADU located within or attached to a principal structure shall not occupy an entire floor of the principal structure and shall not exceed 40 percent of the gross floor area of the principal structure. The gross floor area of an ADU located within an accessory structure that is detached from the principal structure shall not exceed 40 percent of the gross floor area of the principal structure.
Manchester scrapped its old zoning code (Chapter 155, in effect since 2001) and adopted a brand-new ordinance on December 16, 2025 that took effect March 1, 2026 — after the July 2025 state ADU law (HB 577) was already in force. It shows: unlike many NH towns still catching up, Manchester's drafters wrote several of the new state protections directly into the text.
What you get, by right, with just a building permit — no Planning Board hearing, no Conditional Use Permit, no Special Exception: one ADU, attached or detached, in R-S, R-1A, R-1B, R-2, R-M, MX-1, MX-2, or BC-1 (basically every district that allows a single-family house). Your ADU can go inside the house, in an addition, above or inside an existing or new garage, or as a freestanding structure. It can be up to 950 sq ft, and the ordinance explicitly guarantees you can't be forced below 750 sq ft even under the percentage-based caps. You get to choose whether the one required extra parking space goes on your lot or at an off-site dedicated spot. Converting an existing structure (like an old garage) is protected from current setback/lot-coverage rules — as long as that structure existed before July 1, 2025 (a town-added wrinkle the state statute doesn't actually require — worth challenging if your situation doesn't fit).
Where it gets tougher than the law requires: if you build your ADU as a detached structure, the city imposes a minimum window-coverage percentage and mandates a pitched roof — standards it does not apply to the main house. State law says a town can only hold your ADU to the same aesthetic bar as an ordinary house, so this looks like overreach. Second, Manchester doesn't just require owner-occupancy of one unit (which the state law allows) — it requires you to record a permanent deed restriction saying so, forever, before you can get your certificate of occupancy. That's a real, lasting encumbrance on your title that state law doesn't clearly authorize. Third — and this doesn't conflict with the ADU statute, but it matters for your business plan — short-term rental (Airbnb-style, under 30 days) is flatly banned in every purely-residential district where ADUs are actually allowed (R-S, R-1A, R-1B, R-2, R-M). If you're building an ADU as a rental investment, plan on a long-term or medium-term tenant, not nightly guests, unless you're in one of the mixed-use/business districts where STR needs a Special Exception anyway. Finally, expect an ADU-specific impact fee (roughly $2,000 combined) due at permitting — legal, but a real cost to budget for.
Primary source: Town zoning ordinance (PDF) — Ordained December 16, 2025
Get a free personalized report for your address in Manchester — including where the 2025 law works in your favor.
Get My Free Manchester ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Manchester's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Manchester allows one accessory dwelling unit (attached or detached) by right in every zoning district that permits a single-family house. 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.
950 sq ft — confirmed with the town. State law doesn't let any town cap ADU size below 750 sq ft.
Attached + detached (By right, building permit only). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 Spot for ADU on site or off-street — confirmed with the town. 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.