Portsmouth ADU Guide: Your Path to More Affordable Living

The 2025 Portsmouth, NH Accessory Dwelling Unit (ADU) Handbook is finally here. It provides a comprehensive guide for homeowners interested in creating ADUs on their property.

Here’s a summary of the key points:

What is an ADU?

• An ADU is a self-contained residential unit on the same property as a single-family home. It includes a living area, kitchen, bathroom, and sleeping facilities.
• ADUs can be attached or detached and offer a way to increase housing options without additional land development.

Benefits of ADUs

• Increase housing affordability and diversity.
• Provide supplemental income for homeowners.
• Allow family members to live nearby while maintaining independence.
• Support aging in place.

Types of ADUs

• Attached ADUs (AADU): Internal conversion, garage renovation, outward expansion, upward extension.
• Detached ADUs (DADU): Garage, barn, or carriage house conversions.

Planning and Design

• Homeowners should assess neighborhood compatibility, property layout, and lifestyle needs.
• ADUs must adhere to zoning regulations regarding size (maximum of 750 sq ft), height, and parking (1 off-street space).
• Design considerations include materials, sustainability, privacy, and integration with the main home’s architecture.

Approval Process

1. Plan: Clarify objectives and assess property.
2. Design: Develop detailed plans and layouts.
3. Apply: Submit an application through the City’s OpenGov portal.
4. Review: Staff evaluates the application for compliance with zoning regulations.
5. Approval: Obtain necessary permits (Administrative Approval or Conditional Use Permit).
6. Create: Begin construction and inspections.
7. Occupancy: Receive a Certificate of Use and Certificate of Occupancy.

Frequently Asked Questions

• Only one ADU per property is allowed.
• ADUs cannot be sold separately from the main home.
• ADUs require owner-occupancy (either in the main house or the ADU).
• A minimum of one off-street parking space is required.

Resources

• Homeowners are encouraged to meet with City staff, use online mapping tools, and consult professionals for design and construction.
• The handbook provides links to zoning ordinances, application forms, and contact information for City departments.

The handbook serves as a step-by-step resource to help homeowners navigate the process of planning, designing, and building an ADU in Portsmouth, ensuring compliance with local regulations and enhancing property value.