ADUs Now Allowed By Right Across New Hampshire

With HB 577 officially signed into law, New Hampshire has cleared the path for more housing across the state—starting July 1, 2025. 

⏰ TLDR:

Towns can no longer block ADUs through indirect means like oversized septic demands.

⚖️ Why It Matters

• Cuts red tape for homeowners looking to build rental or in-law units

• Opens up housing options in every part of the state, including rural and exclusionary areas

• Standardizes rules across 234 municipalities, reducing confusion and local resistance

   

🔎 Zoom In: What the Law Says

• Allowed by Right: One ADU on every lot with a single-family home

• Silent Towns: Even if local ordinance says nothing, ADU is still allowed

• Size: Default max 950 sq ft. Towns may allow more or lower it, but not below 750 sq ft

• Zoning Rules: ADU can’t be subject to stricter lot size, frontage, or setback rules than a single-family home

• Parking: Max of one additional space required

• Owner-Occupancy: Town may require owner to live on-site, but can’t dictate which unit.

• Occupancy Rules: No requirement that ADU residents be related

📎 The Deets

• Law: HB 577 (Chapter 197)

• Signed: July 15, 2025

• Effective: July 1, 2025

   

Applies to all zoning districts where single-family homes are allowed.

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