ADU Rules in Derry, New Hampshire

Derry is a southern New Hampshire town with a population of approximately 34,000 — one of the largest towns in the state. Located in Rockingham County, Derry is best known as the birthplace of poet Robert Frost (the Robert Frost Farm State Historic Site is on Derry's Rockingham Road) and as a bedroom community for both Manchester and the greater Boston metro area. Derry is governed by a Select Board and Town Administrator under the traditional New England town meeting form of government. Property owners benefit from New Hampshire's statewide ADU law, which applies in full to towns as well as cities.

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

New Hampshire's RSA 674:71-73 (enacted 2017, strengthened by 2021 amendments) is New Hampshire's foundational ADU mandate:

• One ADU by right: The Town of Derry must allow at least one accessory dwelling unit as of right on any single-family residential lot. No variance, special exception, or Town Meeting vote is required to exercise this right.
• Administrative approval: ADUs meeting local dimensional standards must receive administrative approval without a public hearing or Zoning Board of Adjustment review.
• Owner-occupancy: The 2021 amendment (RSA 674:73) restricted conditions municipalities can impose, including owner-occupancy requirements. Verify Derry's current local conditions with the Planning Department.
• State law prevails: Any Derry local zoning provision conflicting with RSA 674:71-73 is superseded by state law.

Permitted ADU Types in Derry

• Detached ADU: A standalone accessory structure on the same lot as the primary single-family home
• Attached ADU: An addition to the primary home with a separate, private entrance
• Interior ADU: A unit carved from the existing home — basement apartment, converted garage bay, or upper-floor unit
• Garage conversion: Converting an attached or detached garage into a self-contained dwelling

Confirm which ADU types are permitted in your specific zoning district with Derry's Planning Department.

General Size and Dimensional Standards

Derry's zoning ordinance details vary by district. Confirm all current standards with the Planning Department.

Special Overlay Considerations

Manchester-Boston Regional Airport (MHT) Proximity: MHT is located in Manchester, just to the northwest of Derry. Some Derry properties — particularly in the northwestern sections of town — may be affected by airport noise contours or approach path overlays. These overlays may require noise attenuation in residential construction or restrict new dwelling units in the most affected areas. Verify your parcel's airport overlay status with Derry Planning before finalizing any ADU design.

Boston Commuter Character: Derry is firmly in New Hampshire's southern commuter belt. With no state income tax and easy access to I-93 and Route 28, Derry attracts Massachusetts workers. ADU rental demand in Derry is driven by commuters, making ADUs a practical income-generating investment.

Floodplains: The Beaver Brook and other waterways flow through Derry. Properties near these waterways may be in FEMA Special Flood Hazard Areas. Check your FEMA flood map status and comply with Derry's Floodplain Management Ordinance if applicable.

Town Meeting and Local Governance

As a New England town, Derry's zoning ordinance is adopted and amended through Town Meeting — the annual gathering of registered voters who vote directly on ordinance changes. This means:

• ADU-related zoning changes require Town Meeting approval (major changes cannot be made between annual meetings).
• RSA 674's statewide mandate already provides ADU rights regardless of local zoning text.
• The Derry Zoning Board of Adjustment (ZBA) hears variance and appeal cases; the Planning Board handles subdivision and site plan review.

Permit Process

1. Zoning verification: Confirm your lot's zoning district and any overlay zones with Derry Planning.
2. Pre-application consultation: Meet with planning staff to discuss your ADU concept early.
3. Plan preparation: Work with a licensed architect or designer; plans must conform to NH State Building Code (RSA 155-A, IBC/IRC based).
4. Building permit application: Submit to the Derry Planning & Zoning or Building Inspection office.
5. Administrative review: Code-compliant ADUs receive administrative approval under RSA 674 — no public hearing required.
6. Inspections: Schedule and pass all required construction inspections.
7. Certificate of occupancy: Obtain CO before occupying the ADU.

Contact Information

• Town of Derry Planning Department: derry.nh.gov
• Municipal Code: library.municode.com/nh/derry

Disclaimer

ADU regulations in Derry 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 Town of Derry Planning 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.