New Hampshire's New ADU Law: What HB 577 Means for Homeowners in 2026

The short version

In July 2025, New Hampshire signed HB 577 into law, amending the state's ADU statute (RSA 674:71–73). It is now in effect — and it is the single biggest expansion of homeowner building rights in New Hampshire in a decade. If a town's zoning allows a single-family home on your lot, the town must now allow you one accessory dwelling unit, attached or detached, as a matter of right.

If you've been told any time in the past few years that your town "doesn't allow backyard cottages" — that answer is very likely out of date.

What HB 577 actually changed

Under the old law (in place since 2017), towns only had to permit *attached* ADUs — an in-law apartment over the garage or off the back of the house. Detached units were optional, and many Lakes Region and Seacoast towns simply didn't allow them, or buried them under special-exception hearings.

HB 577 changes the ground rules:

• Detached ADUs are now allowed by right. One ADU — attached or detached — must be permitted wherever single-family dwellings are.
• No special exception or conditional use permit. Towns may not force your ADU through a discretionary hearing. If a single-family house is allowed, so is your ADU.
• Size is protected. A municipality cannot restrict an ADU's living space below 750 sq ft, and cannot cap it under 950 sq ft — which comfortably fits most of our model lineup, including two-bedroom layouts like The Spruce.
• No stacked-on requirements. Towns can't demand extra lot size, setbacks, frontage, aesthetic or design review beyond what a single-family home without an ADU would need.
• Septic stays a state matter. A town may not impose stricter septic requirements on a home with an ADU than the NH Department of Environmental Services itself requires.

What it means town by town in the Lakes Region

We build across the Lakes Region and Seacoast — Wolfeboro, Ossipee, Alton, Moultonborough, Laconia, Rochester, and Dover. Local ordinances are still catching up to the state law, and that gap is exactly where projects stall: a zoning office working from last year's ordinance can send you in circles the statute no longer allows.

Two Lakes Region realities the new law does *not* erase:

1. Shoreland and steep-slope rules still apply. Waterfront and near-water lots in Wolfeboro, Alton, and Moultonborough still run through shoreland protection standards — that's about the *site*, not the ADU. 2. Your septic still has to carry the bedrooms. The state (NHDES) sizes septic systems by bedroom count. Adding an ADU usually means evaluating — and sometimes expanding — the system. As a DEP-certified septic installer with our own excavation fleet, that's work we price into the build from day one instead of leaving as an exclusion.

Rental income math just got better

A detached one-bed in the Lakes Region typically rents long-term for $1,400–$1,900/month — more near the lakes in season. With detached units now buildable by right, the rental-income case for an ADU applies to thousands of NH lots that were shut out before HB 577. Financing has caught up too: see our financing page for monthly payment options, HELOCs, and DSCR rental loans.

How to move on this

1. Confirm your lot qualifies — if a single-family home is allowed, your ADU now is too. 2. Get the site evaluated — septic capacity, access, clearing, and grading determine your real all-in number. Book a free consultation and we'll walk it with you. 3. Pick a model — all 7 of our models are priced up front, and three display models are under construction right now. 4. Permit with a complete package — we submit site plan, elevations, septic load calc, and erosion control together, which is how approvals move fast even in towns still adjusting to the new law.

New Hampshire just handed homeowners a right they've never had. The builders who know the statute — and own the equipment to deal with the dirt — are how you actually use it.