NH'S ADU LAW CHANGED.
YOUR LOT QUALIFIES.
New Hampshire HB 577 amended RSA 674:71-73 effective July 1, 2025. In plain English: every single-family lot in NH can now have one ADU by-right. Detached ADUs are allowed. Towns can't add ADU-specific setbacks — they have to use the same setbacks they use for your existing house.
What changed
- • By-right statewide. Towns can no longer require special permits, hearings, or discretionary review for a compliant ADU.
- • Detached now allowed. Previously many towns only permitted attached ADUs. That's gone.
- • No owner-occupancy requirement. You can build, rent both units, and live elsewhere.
- • Setbacks match the single-family lot. If your main house can be 25 ft from the side property line, so can your ADU.
- • Detached ADUs capped at 950 sf. Attached can sometimes exceed it depending on the town.
What didn't change
- • Town lot-coverage limits, fire-separation, and dimensional standards still apply.
- • NH DES wetland setbacks (75 ft buffer) and shoreland protection still apply.
- • Septic / on-lot wastewater rules — including 75 ft from leach field — still apply.
- • You still need a building permit. We pull it for you.
Attached vs detached — the one nuance
The statute permits towns to require attached ADUs to follow the principal dwelling's existing setback footprint instead of detached-ADU rules — and attached units can sometimes exceed the 950 sf cap depending on the town. Our visualizer treats your placement as detached by default. If you're considering an attached layout, we verify the math with your town directly before locking the price.
Why this matters for your lot
The state law is one thing. How it actually lands in your town's planning office is another. We've been pulling permits in NH and ME for years — Durham, Dover, Newfield, Wakefield, Madbury — and we know which towns are clean by-right approvals and which ones still want a chat with the planner. That's the difference between a price quote and keys in 12 weeks.