ADU Rules in Dover, New Hampshire

Dover is the oldest city in New Hampshire and the county seat of Strafford County, with a population of approximately 32,000. Located along the Cocheco River in the Seacoast region, Dover has a strong historic character and a growing housing market influenced by its proximity to the University of New Hampshire (in neighboring Durham) and the broader Portsmouth–Dover–Rochester corridor. Property owners benefit from New Hampshire's statewide ADU law, which applies in full in Dover.

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

New Hampshire's RSA 674:71-73 (enacted 2017, strengthened by 2021 amendments) is the legal backbone for ADU construction in Dover:

• One ADU by right: Dover must allow at least one accessory dwelling unit as of right on any lot containing a single-family dwelling in a residential zone.
• No discretionary barrier: Code-compliant ADUs receive administrative approval — no public hearing, variance, or special exception is required under state law.
• Owner-occupancy: The 2021 amendment (RSA 674:73) restricted the conditions municipalities can impose on ADU construction. Verify Dover's current local conditions with the Planning Division.
• State law prevails: Where Dover's local zoning conflicts with RSA 674:71-73, state law controls.

Permitted ADU Types in Dover

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

Contact Dover's Community Services — Planning Division to confirm which ADU types are permitted in your specific zone.

General Size and Dimensional Standards

Always confirm current dimensional standards with Dover's Planning Division, as requirements vary by district.

Special Overlay Considerations

Cocheco River Flood Zones: The Cocheco River flows through Dover, and riverside properties may be in FEMA AE or other Special Flood Hazard Areas. ADUs in flood zones must meet elevated construction standards under Dover's Floodplain Management Ordinance.

Historic Areas: Dover's downtown and older residential neighborhoods may include historic preservation overlay zones. Exterior modifications — including new ADU entrances, additions, and detached structures — may require review by Dover's Historic District Commission in designated areas. Interior conversions are typically less constrained.

Seacoast Region Housing Demand: Dover is part of the NH Seacoast region where housing costs are relatively high. ADUs can provide rental income while supporting housing supply, consistent with the intent of RSA 674.

Permit Process

1. Zoning verification: Confirm your lot's zoning district and any overlays via Dover's zoning map or the Planning Division.
2. Pre-application meeting: Discuss your project with Planning Division staff before finalizing plans.
3. Plan preparation: Work with a licensed architect or designer; plans must comply with the NH State Building Code (RSA 155-A, IBC/IRC based).
4. Building permit application: Submit to Dover Community Services — Building Inspection.
5. Administrative review: No public hearing required for code-compliant ADUs under RSA 674.
6. Inspections: Schedule all required construction inspections.
7. Certificate of occupancy: Obtain CO before occupying the ADU.

Contact Information

• Dover Community Services — Planning & Zoning: dover.nh.gov
• Municipal Code: library.municode.com/nh/dover

Disclaimer

ADU regulations in Dover 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 Dover Community Services 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.