| Max size | 750 sq fthabitable area; lowest cap state allows |
|---|---|
| Min size | No town minimumbuild as small as code allows |
| Bedrooms | No limit |
| Type | Attached or detacheddetached legalized 3/10/2026 |
| Parking | 1 off-street spacetown says on-site; state gives you choice |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Not statedno STR rule in zoning ordinance |
| 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 Hooksett:
If you own a single-family house in Hooksett's Mixed Use 2 or Mixed Use 5 district, Article 27 reads as if you're simply not allowed an ADU. But state law ties the ADU right to any district where single-family homes are permitted — and both of those districts permit single-family homes. The town's district list did not get updated when Article 27 was rewritten in 2026.
Hooksett rewrote Article 27 in March 2026 to allow detached ADUs, but forgot to update the definitions section (Article 22), which still defines an ADU as something 'within or attached to' the house. If a code officer ever leans on that stale definition to deny a detached unit, they're wrong twice over — the town's own Article 27 AND state law both allow detached. This is a drafting leftover, not a live restriction, but it is worth having the citation ready.
Three things here. First, Hooksett says 'a minimum of one' space — state law makes one the MAXIMUM the town can require, so 'minimum' is backwards and cannot be used to demand a second space. Second, 'off-street' means the town is telling you the space has to be on your own lot; state law says YOU choose whether it sits on your lot or at a legally dedicated off-site spot. Third — and this is the strongest point — the town's power to require even ONE space only kicks in IF it already requires parking for the main house. Hooksett's parking article covers only commercial, industrial and multi-family sites, not single-family homes. On the ordinance's own terms, the trigger for an ADU parking mandate may never fire at all.
Hooksett's ADU permit process is written as though there's already a house standing that you're modifying — 'proposed changes to the building,' application by 'the owner of the primary unit.' State law expressly lets you build a new house and its ADU together in one project. You don't have to build the house first and retrofit later.
Hooksett set its cap at exactly 750 sq ft — the lowest number state law lets a town choose. That is legal on its face. The gray area is the word 'habitable': if the code officer measures 'habitable area' in a way that excludes things like bathrooms, closets, hallways or stairs, the real-world buildable size drops BELOW the 750 sq ft that state law guarantees as the minimum allowable cap. Worth pinning down with the Code Enforcement Officer in writing before you design.
Hooksett may hold your ADU to a look-and-feel standard ONLY if it holds ordinary houses to the same standard — and it doesn't. Nothing in Hooksett's zoning ordinance imposes any aesthetic or design-review requirement on a regular single-family house. §C.11 singles the ADU out, which is exactly what RSA 674:72, VII forbids. If the code officer tries to use 'aesthetic continuity' to make you change siding, roof pitch or windows, the statute is squarely on your side.
Hooksett rewrote its ADU rules at the ballot box on March 10, 2026. Zoning Amendment No. 6 passed 1356 to 836, and Article 27 of the Zoning Ordinance now carries the heading 'ACCESSORY DWELLING UNITS (Amended 3/10/26).' The headline: DETACHED ADUs ARE NOW LEGAL in Hooksett. The old ordinance said flatly, 'Detached accessory dwelling units are prohibited.' That sentence is gone. The town also added a genuinely homeowner-friendly clause (§C.12) letting you convert an existing structure — 'including but not limited to detached garages' — into an ADU even if that structure doesn't meet today's setback or lot-coverage rules. That is a real win and puts Hooksett ahead of several neighboring towns.
⚠️ THE TRAP: the Community Development page on the town's own website is still serving 'Zoning Ordinance 2024 Revised.pdf,' and that document still contains the repealed detached-ADU ban. If you or your builder downloads the ordinance from the obvious link, you will read a rule that is no longer the law. The current text is in 'Zoning Ordinance 2026.pdf.'
WHAT YOU GET: One ADU per single-family home, attached or detached. Permit is administrative — you apply to the Code Enforcement Officer with an owner-occupancy letter, a floor plan, a site plan and a fee. No ZBA hearing, no special exception, no Planning Board site plan review. You must live on the property, but YOU choose which unit — the house or the ADU. No cap on bedrooms. No minimum size. No short-term-rental restriction anywhere in the zoning ordinance. Separate water and septic systems are expressly not required. Height limit is the district's normal 35 feet; a new detached ADU over 200 sq ft has to meet the same setbacks as a regular house (in LDR that's 35 ft front / 25 ft rear; in URD it's 25 ft front / 15 ft side / 15 ft rear) — but again, a CONVERSION of an existing structure is exempt from those setbacks entirely.
WHERE HOOKSETT IS STINGY (but legal): the size cap is 750 sq ft of 'habitable area,' flat, for every ADU. 750 is the absolute smallest maximum any NH town is allowed to set — the state's default is 950 sq ft — so Hooksett went straight to the floor. And note this is actually a DOWNGRADE for owners of larger homes: the old rule let you build up to 30% of your primary dwelling if the house was over 2,500 sq ft (so ~900 sq ft on a 3,000 sq ft house). The new flat 750 takes that away. It's legal, but it's the least the town could have offered. One more thing to nail down in writing with the Code Enforcement Officer: the ordinance never defines 'habitable area.' If it's measured to exclude bathrooms, hallways or stairs, your usable ADU could shrink below the 750 sq ft floor state law contemplates.
WHERE STATE LAW BEATS THE TOWN — five things the ordinance doesn't tell you: (1) PARKING. Article 27 says 'a minimum of one (1) off-street parking space.' Backwards on every count. State law makes ONE space the MAXIMUM the town can require, and it gives YOU — not the town — the choice of putting that space on your lot or at a legally dedicated off-site location. Bigger still: RSA 674:72, IV only lets a town require an ADU space IF it already requires parking for the main house — and Hooksett's parking article (Art. 17) applies only to commercial, industrial and multi-family sites, not to single-family homes. On the town's own terms, the trigger for an ADU parking mandate may never fire at all. (2) DISTRICTS. Article 27 lists only LDR, MDR and URD. But Mixed Use District 2 and Mixed Use District 5 both permit single-family homes, and state law ties the ADU right to any district where single-family homes are allowed. If you own a single-family house in MUD2 or MUD5, the town's list omits you — state law does not. (3) BUILD TIMING. The permit section is written as though a house already exists ('proposed changes to the building,' application by 'the owner of the primary unit'). State law expressly lets you build the ADU at the same time as a brand-new principal dwelling. You do not have to build the house first and retrofit. (4) THE DEFINITION LEFTOVER. Article 22 (Definitions) was never updated — it still defines an ADU as a unit 'within or attached to a single-family dwelling.' That's a stale drafting artifact contradicted by the town's own Article 27 and by state law. If anyone waves it at you, you have two authorities to point to. (5) AESTHETICS. §C.11 requires 'aesthetic continuity with the principal dwelling unit.' RSA 674:72, VII lets a town apply aesthetic standards to an ADU ONLY IF it applies the same standards to the principal dwelling — and Hooksett imposes no aesthetic or design-review standard on ordinary single-family houses anywhere in its zoning ordinance. The clause singles the ADU out, which is precisely what the statute forbids.
The one thing genuinely left open: the ordinance never defines 'habitable area' (§C.6). If the Code Enforcement Officer measures it in a way that excludes bathrooms, hallways or stairs, your usable ADU could shrink below the 750 sq ft that state law guarantees as the smallest allowable cap. Get that definition in writing before you design.
Primary source: Town zoning ordinance (PDF) — Article 27 last amended 3/10/2026 (the ordinance's own…
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Get My Free Hooksett ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Hooksett's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Hooksett allows one accessory dwelling unit, attached OR detached, by right (Code Enforcement Officer permit only, no board hearing) in its LDR, MDR and Urban Residential districts. 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.
750 sq ft — habitable area; lowest cap state allows. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or detached (detached legalized 3/10/2026). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 off-street space — town says on-site; state gives you choice. 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.