| Max size | 1,100 sq ftconfirmed with the town |
|---|---|
| Min size | 650 sq ftconfirmed with the town |
| Bedrooms | Up to 2confirmed with the town |
| Type | Attached by rightdetached needs a Planning Bd permit |
| Parking | 1 spot for ADUconfirmed with the town |
| 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 Amherst:
Since July 2025, state law entitles you to build one detached ADU by right, with only a building permit — no hearing required. Amherst's ordinance still says you must go through a discretionary Planning Board hearing (Conditional Use Permit) to convert a garage or build any detached accessory apartment, but state law now overrides that requirement. This is the single biggest gap in Amherst's ordinance and the ADU section appears untouched since at least 2016.
State law says a nonconforming setback or lot-coverage objection can't be used against you: converting an existing structure — like a garage that sits closer to the property line than current rules allow — into an ADU must be permitted. Amherst's ordinance, as written, still gives the Planning Board discretion to deny a conversion on exactly that basis, but state law overrides it.
CONFIRMED WITH THE TOWN (July 20, 2026) — ADUs allowed: 1; maximum size 1,100 sq ft; minimum size 650 sq ft; up to 2 bedrooms; impact fees: $4.93psf; parking: 1 spot for ADU; detached-unit distance rule: no; setbacks: Most common zone is RR (residential rural). Setbacks here are 50' front, 25' side and rear.. Town contact: John Yule building department.
There are some designated scenic residential roads in Amherst, and those have larger front setbacks of 100'
Start with the state-law baseline: since July 1, 2025, New Hampshire law (RSA 674:71-73, as amended by HB 577) entitles you to one accessory dwelling unit — attached or detached — by right in any district that allows single-family homes, with no special exception, conditional-use permit, or board hearing for that one by-right unit. Amherst's zoning ordinance addresses ADUs under Section 3.5, 'Accessory Apartments,' which shows no amendment since March 12, 2019 (and March 8, 2016 for the permitted-use table entries) — meaning it entirely predates the 2025 state law and has not been updated to match it. What the town's ordinance provides: an attached accessory apartment (structurally integrated into the primary home) is allowed by right — no special exception or hearing — in all three of Amherst's single-family residential zones: Residential/Rural (2-acre minimum lots), Northern Transitional (3.5-acre minimum), and Northern Rural (5-acre minimum). It can be up to 70% of the primary home's gross heated floor area, capped at 1,100 sq ft (more generous than the state's 950 sq ft default cap — towns are allowed to authorize more), with no more than 2 bedrooms and no minimum size specified. Only one accessory apartment is allowed per lot, it can't be sold or conveyed separately from the main house, and it's barred on townhouse/duplex-style attached housing, condos, and manufactured housing — all consistent with the state law's carve-outs. Where the town's text is now overridden by the state floor: (1) the ordinance still says a DETACHED accessory apartment — e.g., converting a garage or barn — requires a full Conditional Use Permit from the Planning Board under Section 3.18, including a hearing and findings on dimensional conformance, neighborhood impact, and 'rural aesthetic and character.' State law now requires towns to permit one detached ADU by right, same as attached, so that hearing requirement no longer controls. (2) The ordinance states no exemption letting a nonconforming (too-close-to-the-line) existing structure be converted into an ADU — and the CUP process actually asks the Planning Board to confirm dimensional conformance, the opposite of the state-mandated protection; state law overrides here too. (3) Parking, owner-occupancy, entrance choice, electrical service, and short-term-rental rules are simply not addressed in the zoning ordinance — which means Amherst isn't imposing anything unlawful on those fronts, and the homeowner protections state law now guarantees by default (e.g., choice of on-site/off-site parking, choice of entrance) apply regardless. Given the ordinance's age, it's worth a quick call to the Amherst Community Development Office to confirm whether any newer amendment exists before you plan around the older text.
Get a free personalized report for your address in Amherst — including where the 2025 law works in your favor.
Get My Free Amherst ADU Report →House Bill 577 (2025) amended RSA 674:72, effective July 1, 2025. Wherever Amherst's ordinance is stricter than this floor, the state law controls. Read the full NH ADU law explainer →
Yes — and under state law effective July 1, 2025, you're entitled to one accessory apartment by right whether it's attached OR detached. Amherst's ordinance still says a detached unit needs a discretionary Conditional Use Permit hearing, but state law now overrides that. 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.
1,100 sq ft — confirmed with the town. State law doesn't let any town cap ADU size below 750 sq ft.
Attached by right (detached needs a Planning Bd permit). 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.