| Max size | 950 sq ftconfirmed with the town |
|---|---|
| Min size | No town minimum1,000 sq ft table figure doesn't apply |
| Bedrooms | Up to 2confirmed with the town |
| Type | Attached or detacheddetached added March 2026 |
| Parking | 1 Spot Onsiteconfirmed with the town |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Conditional use permit neededdetached ADU can't be short-term let |
| 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 Windham:
This is the big one, and it is genuinely counterintuitive: Windham's March 2026 amendment was SOLD to voters as bringing the ADU rules into compliance with state law — and on most points it did — but on this one point the Planning Board flipped a state-law-COMPLIANT sentence into a NON-compliant one. The pre-amendment draft language said you could convert an old detached garage 'regardless of whether' it violates current setbacks. The version voters actually adopted says you may only convert it if it MEETS current setbacks. Almost no old New England detached garage meets a 30-foot side-yard setback. As written, Windham's ordinance would block the single most common and most affordable ADU project there is. State law overrides it: the conversion must be allowed anyway. If Windham's Building Department tells you no, they are citing a clause that RSA 674:72 preempts.
Windham froze the eligible building stock as of July 1, 2025. That date has no basis in the statute — and it sits oddly next to Windham's OWN definition of an attached unit, which the town amended in the same vote to expressly cover a 'simultaneously constructed detached structure.' Your right to an ADU doesn't expire based on when your garage was built.
Windham gets the count right — one extra space, no more. But it assumes the space is on your lot and behind your one shared driveway. State law gives YOU, not the town, the choice of putting that space on-site or at a legally dedicated off-site location. The single-shared-driveway rule is also a tight fit for a detached ADU on a large Rural lot; state law doesn't authorize a driveway mandate as such, though it doesn't expressly forbid one either.
If your house is held in an irrevocable trust (very common in NH estate planning), or in an LLC with three members, or in an out-of-state entity, Windham's ordinance as written says you may not have an ADU at all — even if you live there full time. No such rule applies to the identical house WITHOUT an ADU. That looks like a requirement 'beyond what would be required for a single-family dwelling,' which RSA 674:72 prohibits, but the statute expressly allows owner-occupancy conditions and a town could argue this is just an anti-evasion mechanic. Genuine gray area — get an attorney before you restructure your title.
Windham makes you record a permanent restriction against your own deed at the county registry before it will let you occupy the ADU. The underlying purpose (no condo-izing the ADU and selling it off) is something the state does let towns prohibit — but forcing a recorded encumbrance on your title, which no ordinary single-family homeowner has to do, is a heavier hand than the statute clearly authorizes. Budget for it and expect it; whether it's enforceable is an attorney call.
In the Village Center District, Windham's cross-reference appears to drag an ADU into full Planning Board site plan review. State law says an ADU can't be saddled with review a regular house wouldn't face. It's not clear the town INTENDED this result — it may just be sloppy drafting in the cross-reference — but if you're in the VCD, flag it early. Most Windham ADU projects are in Rural or Residence A, where this doesn't bite.
If your home is a manufactured house on its own lot, Windham says flatly that you cannot have an ADU — even though the town treats that home as a dwelling for every other purpose. State law guarantees the ADU right to single-family dwellings and separately protects manufactured housing from discriminatory zoning. Whether a manufactured home on a fee lot counts as a 'single-family dwelling' for RSA 674:72 is exactly the kind of question this ordinance forces. If that's you, this is worth an attorney call — it may be the town's weakest clause.
Windham's ordinance says in one breath that no extra aesthetic rules apply to your ADU, and in the next that your entrances must be designed to look like a single-family house. These can be reconciled (the 'looks like a house' rule is mild and Windham's own compliance clause is strong), but the tension is real. In practice this is the least likely of Windham's clauses to cause you a problem.
CONFIRMED WITH THE TOWN (July 30, 2026) — ADUs allowed: 1; maximum size 950 sq ft; up to 2 bedrooms; parking: 1 Spot Onsite; detached-unit distance rule: No regs for a min or max distance from existing structure; setbacks: No impact fee currently. Town contact: Keith Meile - Building Inspector 603-432-3806.
Pat confirmed requirments on August 12, 2026
Windham rewrote its accessory dwelling unit rules at the March 10, 2026 town election. Planning Board Amendment #4 — described on the ballot as bringing Section 602.1.9 into compliance 'with provisions of State law' — passed 1,950 to 869. So Windham's posted 2026 zoning ordinance is genuinely current (we verified the posted PDF's text against the adopted ballot language rather than assuming it), and on most counts Windham now looks BETTER than its neighbors.
WHAT YOU GET. One ADU per single-family home, attached or detached, by right — no ZBA hearing, no special exception, no conditional use permit — in the Rural District and Residence Districts A, B and C (the districts where nearly every Windham house sits). Up to 950 sq ft of occupied floor space, up to two bedrooms. Height is the normal 35-foot town-wide limit. Setbacks are just the ordinary single-family setbacks for your district (in Rural and Residence A: 50 ft front, 30 ft side, 30 ft rear, 20% max building coverage). One extra off-street parking space. You must live in one of the two units, but Windham does NOT tell you which one. And unusually for this county, Section 602.1.9.3.4.1 explicitly hands YOU the choice of whether an attached ADU gets its own separate entrance or shares the main house's — Derry and Candia both still get that wrong. Windham's Section 602.1.9.3.3 also flatly promises no extra lot size, setback, frontage, aesthetic, or design-review requirements beyond a normal house. That is a strong, homeowner-friendly clause.
WHERE WINDHAM STILL OVERREACHES — AND THIS IS THE ONE THAT MATTERS. In the very same March 2026 amendment, the Planning Board changed one sentence in a way most voters would never have caught. Section 602.1.9.3.10 now reads that you may convert an existing structure — 'including but not limited to detached garages' — into an ADU 'PROVIDED THAT such structures MEET current dimensional requirements for setbacks or lot coverage.' The Planning Board's own December 2025 markup shows the original draft said you could convert it 'REGARDLESS OF WHETHER' it violated those setbacks. They struck the compliant version and adopted the non-compliant one. This matters enormously, because the cheapest ADU in New Hampshire is almost always an old detached garage — and old detached garages almost never sit 30 feet off the side line. RSA 674:71-73, as amended by HB 577 effective July 1, 2025, requires towns to allow that conversion even when the structure is setback- or coverage-nonconforming. State law wins. If Windham's Building Department cites 602.1.9.3.10 at you, they are citing a clause the state has preempted. (Note also the same section only lets you convert structures that existed 'on or before July 1, 2025' — another cutoff with no basis in the statute.)
SMALLER SNAGS. (1) Parking: Windham correctly caps it at one extra space, but assumes it's on your lot behind a single shared driveway. State law lets YOU choose on-site or a legally dedicated off-site space. (2) Ownership form: Section 602.1.9.2 says the property may only be owned by natural persons, a REVOCABLE trust, a small NH LLC, or a small NH corporation. If your home is in an irrevocable trust — very common in NH estate planning — Windham's text says you can't have an ADU. No such rule applies to the identical house without an ADU, which is exactly what RSA 674:72 forbids. Gray area; worth an attorney call. (3) You will have to sign and RECORD a restrictive covenant against your deed at the Rockingham County Registry before you get a certificate of occupancy (Section 602.1.9.3.9). Budget the time and the recording fee. (4) Manufactured homes and townhouse-style attached single-families are flatly barred from having an ADU — a shaky exclusion. (5) In the Village Center District only, the cross-reference in 612.1.1 appears to drag an ADU into full site plan review.
THE SHORT-TERM RENTAL TRAP. At the SAME March 2026 election, Windham adopted a brand-new Section 621 (passed 1,758–1,101). Short-term renting — anything under 30 consecutive days — now requires a Conditional Use Permit from the Planning Board, and owner-occupied STRs are permitted ONLY in the Rural and Residence A districts, and ONLY in 'single family residences with a single ATTACHED accessory dwelling unit.' Read that again: if you build a DETACHED ADU, you are not eligible to short-term rent it at all. A citizen petition that would have opened short-term rental to any single-family home and its ADU was defeated 1,131–1,735. Short-term rental is not protected by the state ADU law, so these restrictions are lawful — which means this is the real economic decision in Windham: a detached ADU gives you the better building, an attached ADU gives you the only path to short-term rental income. Long-term (30+ day) renting of either is unaffected.
Bottom line: Windham is one of the more compliant towns in Rockingham County, and its March 2026 rewrite fixed real problems. But 'recently amended' does not mean 'fully compliant' — the garage-conversion setback gate is a live conflict with state law, and it is the one most likely to cost you money.
Primary source: Town zoning ordinance (PDF) — ADOPTED/LAST AMENDED: March 10, 2026 (annual town election,…
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Yes — Windham allows one accessory dwelling unit, attached OR detached, by right in the Rural District and Residence Districts A, B and C. Up to 950 sq ft, max two bedrooms, owner must live in one of the two units. 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 or detached (detached added March 2026). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 Spot Onsite — 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.