New Hampshire Expands ADU Rights: What Homeowners Need to Know
New Hampshire has broadened its Accessory Dwelling Unit (ADU) regulations, making room for greater flexibility in backyard housing. As of July 1, 2025, a newly enacted state law permits both attached and detached ADUs as of right; eliminating the old requirement for an interior connection between units. The new rules make ADU construction a by-right activity, requiring just a building permit.
Why the Change Matters
Previously, state law only allowed ADUs if directly attached to the main house via an interior doorway, limiting opportunities for ADU construction. An attachment requires more up front design/engineering work, limits placement on lots, and often has cost implications that increase total project cost. This was the key change but there are also some other highlights:
New Hampshire cities and towns must now allow one ADU per single-family lot.
Zoning and other controls can’t be more restrictive than for single-family homes. Meaning municipalities may not impose stricter rules on ADUs than they do on the main home. This includes lot coverage, septic systems, parking (limited to one additional space), and exterior aesthetics.
As we have seen in other states, once the state sets the bar with zoning requirements, the permitting process should face fewer zoning hurdles as cities and towns adopt these new rules. Over time, this should help make ADU construction predictable across the state!
Municipalities may not demand separate septic systems, unless already required for the property—helping contain build costs.
With House Bill 577 now in effect, New Hampshire has taken a meaningful step toward addressing the state’s housing challenges. By making ADUs more flexible and accessible—whether attached or detached—the new law opens doors for families, young professionals, and older residents alike. It encourages creative housing solutions that fit within existing neighborhoods, helping communities grow without losing their character.
These changes won’t solve the housing shortage overnight, but they create a pathway for thousands of new homes over time—each backyard unit adding a ripple of opportunity. For many families, this could mean the chance to live closer together, reduce housing costs, or create a new stream of income.
It’s a hopeful sign that New Hampshire is embracing smart, small-scale solutions to build a stronger housing future. And we’re excited to help homeowners turn that opportunity into reality—one backyard home at a time.