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Zoning Guide

ADU Rules in Nashua, New Hampshire

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ADU Rules in Nashua, New Hampshire

Nashua — the Gate City — is New Hampshire's second-largest city, with a population of approximately 91,000. Located directly on the Massachusetts border, Nashua is a major Boston suburb with strong commuter demand that makes accessory dwelling units an attractive investment. Property owners in Nashua benefit from New Hampshire's statewide ADU mandate while working within Nashua's local zoning framework.

New Hampshire Statewide ADU Law (RSA 674:71-73)

New Hampshire's RSA 674:71-73 (enacted 2017, strengthened by 2021 amendments) establishes a statewide right to build ADUs:

  • One ADU by right: Every municipality — including Nashua — must allow at least one accessory dwelling unit as of right on any lot containing a single-family dwelling in a residential zone.
  • Streamlined approval: Code-compliant ADUs receive administrative approval without a public hearing or discretionary review.
  • Owner-occupancy: The 2021 amendment (RSA 674:73) removed mandatory owner-occupancy conditions. Municipalities may impose reasonable conditions consistent with state law, but cannot categorically prohibit ADUs.

Where Nashua's local ordinance conflicts with RSA 674:71-73, state law governs.

Permitted ADU Types in Nashua

  • Detached ADU: A separate structure on the same lot, with its own entrance and utilities
  • Attached ADU: An addition to the primary home creating a self-contained unit
  • Interior ADU: A unit created within the existing home footprint, such as a basement or upper-floor conversion
  • Garage conversion: Converting an attached or detached garage to a habitable dwelling unit

Contact Nashua Planning & Zoning to confirm which ADU types are permitted in your specific zoning district.

General Size and Dimensional Standards

Standard General Guidance
Maximum ADU Size Verify with city — local rules vary by district
Minimum Lot Size Per underlying zoning district
Side/Rear Setbacks Typically 5–10 ft; verify locally
Maximum Height Per underlying zone
Parking Typically 1 additional space; verify locally

Nashua's zoning ordinance details vary by district. Always confirm current standards with Nashua Planning & Zoning before proceeding.

Boston Commuter Market Context

Nashua's position as a Boston commuter hub — with easy access to Route 3 and the Everett Turnpike — creates significant rental demand for ADUs. New Hampshire has no income tax or sales tax, making Nashua attractive to Massachusetts workers who live in NH. ADU owners should be familiar with New Hampshire's landlord-tenant laws (RSA 540 et seq.) and consult a local attorney before entering into rental agreements.

Special Overlay Considerations

Merrimack and Nashua River Flood Zones: The Nashua River meets the Merrimack River in the city. Properties in FEMA AE and other Special Flood Hazard Areas must follow Nashua's floodplain development standards, including finished floor elevation requirements and restrictions on habitable basements.

Daniel Webster Highway Corridor: Commercial development pressure along the Daniel Webster Highway (Route 3) corridor may affect properties in transitional zones. Verify your parcel's zoning district before assuming residential ADU rights apply.

Historic Areas: Nashua's older neighborhoods and downtown area may include historic overlay districts with design review requirements for exterior changes.

Permit Process

  1. Zoning verification: Confirm your parcel's zoning district and any overlay designations using Nashua's online zoning map or by contacting the Planning & Zoning Department.
  2. Pre-application consultation: Discuss your project with Nashua Planning & Zoning staff before investing in design.
  3. Plan preparation: Work with a licensed designer or architect to prepare plans meeting NH State Building Code (RSA 155-A, IBC/IRC based).
  4. Building permit application: Submit plans and application to Nashua Building Safety.
  5. Administrative review: Code-compliant ADUs are reviewed administratively; no public hearing required under RSA 674.
  6. Inspections: Schedule all required inspections during and after construction.
  7. Certificate of occupancy: Receive CO before occupying the ADU.

Contact Information

Disclaimer

ADU regulations in Nashua are subject to change. This page is for informational purposes only and does not constitute legal or planning advice. Always verify current requirements with the City of Nashua Planning & Zoning Department and review NH RSA 674:71-73 for statewide ADU rights. Consult a licensed architect, contractor, or land use attorney before beginning any project.

More about Nashua Zoning

Sources

  1. City of Nashua Zoning Ordinance·library.municode.com·Accessed 2026-04-07·Direct link
  2. NH RSA 674:71-73 — Accessory Dwelling Units·gencourt.state.nh.us·Accessed 2026-04-07·Direct link

FAQ

Are ADUs allowed in Nashua, New Hampshire?
Yes. New Hampshire RSA 674:72 requires Nashua to allow at least one accessory dwelling unit as of right on any single-family lot in a residential zone. Nashua's local zoning ordinance implements this state mandate.
Is Nashua's proximity to Massachusetts a factor in ADU rules?
Not directly — New Hampshire and Massachusetts have separate zoning laws, and Nashua follows NH RSA 674 rather than Massachusetts ADU law. However, Nashua's strong Boston commuter market means ADU rental demand is high, and you should consult NH landlord-tenant law for rental regulations.
Are there flood zone restrictions for ADUs near the Nashua River?
Yes. Properties in FEMA-designated Special Flood Hazard Areas near the Nashua River and Merrimack River confluence must comply with Nashua's Floodplain Management Ordinance, typically requiring elevated finished floors and restrictions on below-grade habitable space.