| Max size | 800 sq ftconfirmed with the town |
|---|---|
| Min size | 300 sq ftconfirmed with the town |
| Bedrooms | Up to 2confirmed with the town |
| Type | Attached or detacheddetached needs 2x min lot size |
| Parking | 1 Spot for ADUconfirmed with the town |
| Owner-occupancy | Requiredin either the ADU or the primary home |
| Short-term rental | Under 4 weeks prohibited |
| 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 Hollis:
Under the 2025 state law, you're entitled to a detached ADU (like a converted garage or standalone cottage) by right regardless of lot size, so long as the ADU itself and setbacks otherwise fit. Hollis's ordinance still says you need a 4-acre lot in the R&A or WSC district just to be eligible — but that acreage-doubling requirement is no longer allowed.
State law entitles you to the same by-right ADU treatment in every district that allows single-family homes. If your lot is in Hollis's Water Supply Conservation zone, the town's own ordinance still sends you to the Board of Adjustment for a special exception — but that hearing requirement no longer applies.
State law gives you the choice — you're not required to build an internal connection to the main house if you'd rather have a fully independent attached unit. Hollis's ordinance still requires a shared internal doorway ('through a common wall') and a design that could be folded back into the house later, but that mandate no longer controls.
State law says the entrance-location choice is the homeowner's. Hollis's ordinance nudges any extra ADU entrance to the side or rear of the house — because it's phrased as 'whenever possible' rather than an absolute ban, it's softer than a hard rule, but to the extent the town enforces it as a requirement, it's overridden.
State law caps any ADU-parking requirement at one extra space — and only if the town already requires parking for the main house, which this ordinance doesn't clearly do. Hollis just says ADU parking must be 'adequate,' with no number. A Code Enforcement Officer demanding more than one space, or refusing an off-site space, would likely be overstepping — but this one needs a direct answer from the town before relying on it.
CONFIRMED WITH THE TOWN (July 16, 2026) — ADUs allowed: 1; maximum size 800 sq ft; minimum size 300 sq ft; up to 2 bedrooms; impact fees: None yet, will be imposed soon; parking: 1 Spot for ADU; detached-unit distance rule: No; setbacks: 35' Front, side and rear. Town contact: Jeff Blackwell - Building Inspector.
An attached accessory dwelling unit shall occupy no more than 30 % of the total heated, above grade floor area of the total dwelling unit, including the accessory dwelling unit.
Detached accessory dwelling units cannot be converted to a principal dwelling unit. No smoke detector requirements specified in zoning.
Start with your rights under state law: since July 1, 2025, RSA 674:71-73 (as amended by HB 577) guarantees one ADU — attached or detached — by right in every district that allows single-family homes, with no special exception or board hearing, entrance choice in the homeowner's hands, and at most one extra required parking space. Hollis's ADU rules live in Chapter IX.K of its Zoning Ordinance, most recently revised April 8, 2026 (following a full recodification on May 20, 2025) — both dates after the state law took effect. The town explicitly says its ADU rules are meant to be 'consistent with RSA 674:72.1,' and several pieces genuinely are: ADUs are a permitted (by-right) use in the Agricultural & Business, Recreational, Residential & Agricultural, Rural Lands, and Town Center districts; only one ADU is allowed per lot; the size cap (800 sq ft, minimum 300 sq ft) is lawful; there's no bedroom cap; owner-occupancy is required of either unit — not specified which — which is a requirement towns may lawfully impose; and detached ADUs are conceptually allowed. But several provisions still lag the 2025 floor, and state law overrides them: (1) a detached ADU is only allowed on a lot with DOUBLE the district's minimum lot size — 4 acres in the town's main residential districts — which conflicts with the state's by-right detached-ADU mandate; (2) the Water Supply Conservation district still requires a Board of Adjustment special exception for an ADU even though single-family homes are permitted there by right, conflicting with the state's no-hearing mandate; (3) attached ADUs must be built with a shared internal doorway connecting to the main house ('through a common wall'), conflicting with the homeowner's state-protected choice of a separate entrance; (4) additional entrances are steered to the side or rear 'whenever possible,' which softens but doesn't fully resolve the state's ban on dictating entrance location; and (5) the ordinance's 'adequate off-street parking' standard for ADUs is undefined, with no general single-family parking baseline to anchor it against the state's one-space cap. See conflicts[] for full citations — despite two rounds of revision since the state law took effect, the acreage gate, the WSC special-exception requirement, and the forced shared-access clause all remain on the books as of April 8, 2026.
Get a free personalized report for your address in Hollis — including where the 2025 law works in your favor.
Get My Free Hollis ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Hollis's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — Hollis allows one accessory dwelling unit, attached or detached, by right in most 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.
800 sq ft — confirmed with the town. State law doesn't let any town cap ADU size below 750 sq ft.
Attached or detached (detached needs 2x min lot size). Since July 1, 2025, state law allows detached ADUs by right statewide — town provisions that prohibited them are superseded.
1 Spot for ADU — 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.