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Zoning Guide

ADU Rules in Concord, New Hampshire

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ADU Rules in Concord, New Hampshire

Concord is New Hampshire's state capital and the county seat of Merrimack County, with a population of approximately 44,000. As the seat of state government and home to the NH General Court (the state legislature), Concord is uniquely positioned at the center of NH housing policy. Property owners in Concord benefit directly from the state ADU mandate their legislature enacted and can build ADUs with strong legal backing under NH RSA 674.

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

New Hampshire enacted RSA 674:71-73 in 2017 — one of the earlier statewide ADU mandates in the Northeast — and strengthened it with 2021 amendments. Key provisions applicable to Concord:

  • One ADU by right: Concord must allow at least one accessory dwelling unit as of right on any single-family residential lot. No special use permit or variance is required for code-compliant ADUs.
  • No categorical prohibition: Concord cannot ban ADUs in residential zones through local ordinance. State law supersedes any conflicting local provision.
  • Owner-occupancy: The 2021 amendment (RSA 674:73) limits the conditions municipalities can impose, including owner-occupancy requirements. Verify current local conditions with Concord Planning.
  • Administrative approval: ADUs meeting local dimensional standards are approved administratively without a public hearing.

Permitted ADU Types in Concord

  • Detached ADU: A separate structure (new construction or converted accessory building) on the same lot as the primary residence
  • Attached ADU: An addition to the primary home with an independent entrance
  • Interior ADU: A unit created within the existing home, such as a basement apartment or upper-floor unit
  • Garage conversion: Conversion of an attached or detached garage to a self-contained dwelling unit

Contact Concord Community Development 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 apply
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

Confirm current dimensional standards with Concord Community Development, as requirements can vary by district and are updated periodically.

Special Overlay Considerations

Merrimack River Flood Zones: The Merrimack River flows through Concord, and properties in low-lying areas along the river may be in FEMA-designated Special Flood Hazard Areas (AE zones). ADUs in flood zones must comply with Concord's Floodplain Management Ordinance, which typically requires elevated construction and restricts habitable basements.

Historic Districts: Concord's neighborhoods near the New Hampshire State House, the downtown commercial area, and older residential streets may be subject to historic preservation review. The Concord Historic District Commission reviews exterior changes in designated areas. Interior ADU conversions are generally less affected, but exterior entrances and additions may require design approval.

State Government Facilities: Properties near the State House, DHHS campus, or other state facilities may be subject to special buffers or zoning overlay provisions. Verify with Concord Planning.

Permit Process

  1. Zoning verification: Confirm your lot's zoning district and overlay designations with Concord Community Development or via the city's zoning map.
  2. Pre-application consultation: Meet with city planning staff to discuss your project before committing to a design.
  3. Plan preparation: Hire a licensed architect or designer to produce plans conforming to NH State Building Code (RSA 155-A, based on IBC/IRC).
  4. Building permit application: Submit plans and application to Concord Community Development — Building Division.
  5. Administrative review: Code-compliant ADUs are reviewed without a public hearing under RSA 674.
  6. Construction inspections: Schedule required inspections during and after construction.
  7. Certificate of occupancy: Obtain CO before the ADU is occupied.

Contact Information

Disclaimer

ADU regulations in Concord 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 Concord Community Development 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 Concord Zoning

Sources

  1. City of Concord 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 Concord, New Hampshire?
Yes. New Hampshire RSA 674:72 requires Concord to allow at least one accessory dwelling unit as of right on any single-family lot in a residential zone. As the state capital, Concord also has direct experience with the legislative intent behind NH's statewide ADU mandate.
Are there historic district restrictions for ADUs in Concord?
Possibly. Concord has historic neighborhoods near the State House and downtown core. Properties within historic overlay districts may require design review from the Historic District Commission before exterior modifications. Interior ADU conversions may have fewer constraints.
Do Merrimack River flood zones affect ADUs in Concord?
Yes. Properties in FEMA Special Flood Hazard Areas along the Merrimack River must comply with Concord's Floodplain Management Ordinance, which typically requires elevated finished floors and restricts below-grade habitable space in flood zones.