The law
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.
- Possible no owner-occupancy requirement — dependent on town. Many NH towns don't require you to live on-site, but some still do — we confirm your town's rule before you build.
- Setbacks match the single-family lot. If your main house can be 25 ft from the side property line, so can your ADU.
- Up to 950 sf — no minimum. When a town's zoning is silent on ADU size, there's no minimum and the cap is 950 sf. A town can't limit you below 750 sf, and some towns allow larger.
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.
Wondering how the law applies to your lot? Let's talk.
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