Portsmouth, NH Zoning Regulations & Building Permits
Official references and local checks
Use the official references below to identify the rules that apply to your address, then confirm parcel-specific requirements with the local authority before filing an application.
Official references
- Population:
- 22,158
- County:
- Rockingham County
- State building code:
- NH State Building Code (based on 2018 IBC)(statewide default)
- State ADU law:
- Yes — New Hampshire RSA 674:71-73 (enacted by SB 146, signed March 2016) requires municipalities that adopt zoning to allow at least one accessory dwelling unit as a matter of right or by conditional use permit/special exception in all zoning districts that permit single-family dwellings. HB 1291 (2024), which would have expanded this to two ADUs by right, passed the House but was killed in the Senate.
- FEMA flood map:
- Search flood zones
- Planning department:
- Portsmouth Planning Department
Before you apply
- Call the Portsmouth Planning Department: (603) 610-7216
- Check FEMA flood zone for your parcel — flood-zone status changes setbacks, foundation requirements, and insurance.
- Check your HOA CC&Rs and recorded deed restrictions — they are common in Portsmouth and frequently restrict ADUs, fences, and exterior changes beyond what zoning allows.
Key Zoning Facts
Portsmouth is a historic coastal city in Rockingham County, New Hampshire, with a population of approximately 22,158 (2020 Census). Located on the seacoast at the mouth of the Piscataqua River, Portsmouth is known for its historic downtown, maritime heritage, and vibrant cultural scene. Land use and development are regulated through the city's zoning ordinance, administered by the Portsmouth Planning Department.
Portsmouth's zoning ordinance divides the city into multiple districts, including several residential zones ranging from Single-Family A (SRA) with 15,000 sq ft minimum lots to General Residence (GR) with 7,500 sq ft minimums. The city also includes Mixed Residence (MR), Central Business District (CBD), General Business (G), Industrial (I), and Waterfront (W) districts.
Key Zoning Districts
Portsmouth's primary residential zoning districts include:
- SRA (Single-Family A) — Minimum 15,000 sq ft lots with 25 ft front, 10 ft side, and 20 ft rear setbacks. Maximum height of 35 ft.
- SRB (Single-Family B) — Minimum 10,000 sq ft lots with 20 ft front, 8 ft side, and 15 ft rear setbacks. Maximum height of 35 ft.
- GR (General Residence) — Minimum 7,500 sq ft lots with 15 ft front, 6 ft side, and 12 ft rear setbacks. Maximum height of 35 ft.
- MR (Mixed Residence) — Mixed residential district allowing various housing types and densities.
Commercial and other districts include:
- CBD (Central Business) — Mixed-use district in Portsmouth's historic downtown core
- G (General Business) — Broad range of retail, office, and service uses
- I (Industrial) — Manufacturing, warehousing, and related industrial uses
- W (Waterfront) — Special district for maritime and mixed waterfront uses
ADU Regulations (Accessory Dwelling Units)
New Hampshire state law (RSA 674:72-73) requires all municipalities to allow ADUs (Accessory Dwelling Units) as a matter of right on any property with a single-family dwelling. Portsmouth must comply with this state mandate. Key points:
- One ADU is permitted per single-family lot
- The ADU may be attached to or detached from the primary dwelling (subject to local standards)
- Municipalities cannot prohibit ADUs but may adopt reasonable regulations regarding size, parking, and other dimensional standards
- Contact the Portsmouth Planning Department for the city's specific ADU application requirements and any local dimensional standards
Building Code
Portsmouth follows the NH State Building Code (RSA 155-A), which is based on the International Building Code (IBC) and International Residential Code (IRC). All construction must comply with the state building code.
Development Process
Development in Portsmouth generally requires obtaining the appropriate permits from the city's planning and building departments. The process typically involves:
- Zoning Verification — Confirm that your proposed use is permitted in the applicable zoning district
- Site Plan Review — For commercial, multi-family, and certain other projects, submit a site plan to the Planning Board
- Building Permit — Apply for a building permit with construction documents
- Inspections — Schedule required inspections during construction
- Certificate of Occupancy — Obtain final approval before occupying the structure
For projects that do not conform to existing zoning, property owners may need to seek a variance or special exception from the Portsmouth Zoning Board of Adjustment (ZBA).
Key Considerations
Before starting any development project in Portsmouth, property owners should:
- Verify the zoning classification of their property
- Review setback, height, and lot coverage requirements for the applicable district
- Check for any overlay districts or special regulations (including historic district and coastal/flood zone requirements)
- Determine if the property is in a flood zone using FEMA's flood map service
- Confirm whether HOA covenants or deed restrictions apply
- Contact the Portsmouth Planning Department at (603) 610-7216 for pre-application guidance
Disclaimer: This guide provides general information about zoning in Portsmouth, NH and should not be relied upon as legal advice. Zoning codes are subject to change. Always verify current regulations with the Portsmouth Planning Department before making development decisions.
Regulatory Layers That Apply in Portsmouth
Your property is subject to ALL of these regulatory layers. Each one can impose additional requirements beyond the others.
Federal
- FEMA flood mapping: check parcel-specific flood-zone status
- View FEMA Flood Map
State — New Hampshire
- Building Code: NH State Building Code (RSA 155-A)
- State ADU Override: Yes (NH RSA 674:72-73 requires municipalities to allow ADUs)
County — Rockingham County
City / Municipal
The municipality's zoning ordinance, building-code enforcement, and local permits form the primary local layer of land-use regulation for your property.
Overlay Districts
No overlay districts identified.
Private Restrictions
- Private covenants, deed restrictions, condominium rules, or association rules can impose requirements beyond zoning.
- Check HOA CC&Rs and deed restrictions for additional requirements.
Statewide Context (New Hampshire)
Local data for Portsmouth is limited. The following state-level facts apply across New Hampshire and are inherited by this page until city-specific details are verified.
- State Building Code
- NH State Building Code (based on 2018 IBC)
- State ADU Preemption
- Yes — state law overrides local rules
- Coastal Zone
- Yes
- Wildfire Zones
- No
ADU Rules in Portsmouth
State law (statewide context, not city-specific):
New Hampshire RSA 674:71-73 (enacted by SB 146, signed March 2016) requires municipalities that adopt zoning to allow at least one accessory dwelling unit as a matter of right or by conditional use permit/special exception in all zoning districts that permit single-family dwellings. HB 1291 (2024), which would have expanded this to two ADUs by right, passed the House but was killed in the Senate.
For local size, setback, and parking specifics, contact the Portsmouth Planning Department.
Permit Costs & Timelines
Check Current Permit Fees & Timelines
Permit fees and review times can vary by project type, scope, valuation, and required approvals. Check the current schedule with the local permitting authority before filing.
Check current Portsmouth permit information →Official Sources
City-specific