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ADU Rules in Merrimack County, New Hampshire

9 towns covered · 1 human-verified · Reconciled with the 2025 state law · Last reviewed 2026-09-10
The short answer
Every town in Merrimack County must allow one ADU — attached or detached — by right on single-family lots.

That's the statewide floor under RSA 674:72, effective July 1, 2025. What differs town to town is the details: size caps, parking, owner-occupancy, and how much of each town's posted ordinance the state law now overrides. Pick your town below for the plain-English breakdown.

Merrimack County towns

Andover

Andover's ADU rules (Article XV) haven't been touched since March 2017 — years before the state's by-right detached-ADU law took effect — so several…

Read the full Andover ADU guide →
Boscawen

Boscawen is one of the good ones: at its March 10, 2026 town meeting voters passed a five-part zoning overhaul (ADU article 107-30) that deliberately…

Read the full Boscawen ADU guide →
Bow

Bow's ADU ordinance and its own homeowner infographic were last updated in 2024 — before the July 2025 state law made detached ADUs a by-right use…

Read the full Bow ADU guide →
Concord

Concord passed a thorough October 2025 rewrite that brings its ADU rules in line with the new state-law floor — but the old 2017-era terms (750 sq ft…

Read the full Concord ADU guide →
Epsom ✓ Human-verified

Yes — Epsom allows one ADU (verified with the town), up to 850 sq ft.

Read the full Epsom ADU guide →
Franklin

Franklin rewrote its ADU rules in 2026, swapping a discretionary special-exception process for an administrative by-right permit with a 750-950 sq ft…

Read the full Franklin ADU guide →
Hooksett

Hooksett voters legalized detached ADUs on March 10, 2026 — but the ordinance PDF still posted on the town's own website says detached ADUs are…

Read the full Hooksett ADU guide →
Hopkinton

State law now overrides several of Hopkinton's ADU rules in your favor: the town's ordinance (§3.12, untouched since March 2019) still demands two…

Read the full Hopkinton ADU guide →
Newbury

The July 2025 state law guarantees one ADU by right — but Newbury's ordinance, last revised March 28, 2023, hasn't caught up: Blodgett Landing still…

Read the full Newbury ADU guide →

Not sure what your lot allows?

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Learn the statewide law

Wherever a town's rules are stricter than the state floor, the state law controls. Read the full New Hampshire ADU law explainer →

Other counties

Rockingham CountyHillsborough CountyStrafford CountyBelknap CountyCarroll CountyGrafton County
This guide is an independent informational resource, not legal advice; confirm details with your town's planning department before you build.