ADU Rules: Manchester vs Nashua

Can I build an ADU on my property?

Yes, NH RSA 674:71 to 73 requires all municipalities to allow ADUs by right in zones permitting single-family dwellings.

Do I need to live on the property with an ADU?

Yes, the property owner typically must occupy either the primary dwelling or the ADU. Check Manchester specific requirements.

Can I build an ADU in Nashua?

Yes — and the state mandate makes it strongly favored. NH RSA 674:71-:73 (as amended by HB 577, effective July 1, 2025) requires Nashua to allow one accessory dwelling unit (attached or detached) by-right on every single-family lot. The unit must be allowed up to 750 sq ft minimum (with a 950 sq ft default ceiling, which Nashua may raise), may have more than one bedroom, and may be built either as a new structure or converted from an existing detached garage or accessory building — even if the existing building does not meet current setbacks. Nashua's pre-2025 Land Use Code Sec. 190-32 (700 sq ft cap, family-rental restriction, Special Exception) is preempted to the extent it conflicts. Confirm current Nashua standards with the Planning Department before applying.

Does Nashua still require my ADU tenant to be a family member?

No. NH RSA 674:73 expressly prohibits any local rule requiring residents of the two dwelling units to be related by blood, marriage, or adoption. Nashua's pre-2025 Sec. 190-32 — which limited ADU rental to 'blood or marriage relatives' — is preempted by state law as of July 1, 2025. Nashua may still require that the property owner occupy one of the two units (either the principal dwelling or the ADU) and may require a covenant recorded at the Hillsborough County Registry of Deeds, but it cannot dictate which unit the owner lives in and cannot require family-only rental.