Each application for a potential ADU is unique. We encourage you to come in and meet informally with the Planning Staff to discuss before making a formal application.  

There are two types of ADU – Attached and Detached – that can be created on a single-family property.  

1. Attached: An Attached ADU is conversion of interior space, an addition to the side or on a single-family residence. Interior renovations will require Administrative Approval. Additions will require Planning Board approval through a Conditional Use Permit.  

2. Detached: A Detached ADU will require Planning Board approval through a Conditional Use Permit. 

Staff will review each application and determine what the permitting process will require. After our informal meeting and you decide to create an ADU, a land use application must be made. This can be done using the online permitting program OpenGov. Planning and Sustainability staff will then work with you on the permitting process, making requests for any additional information if required and scheduling your application for an Administrative Approval or Planning Board review. 

Depending on the height and location of a retaining wall, zoning review and a building permit may be required.  Please contact the Planning & Sustainability Department at 603-610-7216 or the Inspections Department at 603-610-7243 for a preliminary review of your retaining wall. 

We may have a subdivision or site plan on file for your property. It is unlikely that we will have a residential plot plan on file in the Planning Department, but you may want to make an appointment to review our files. Please contact the Planning Department at (603) 610-7216 and we can determine what we may have on file for your property. For review of the Inspections Department files please contact them at (603) 610-7243. 

You can find your Zoning District by searching for your property on MapGeo. Type in your address in the “Property Quick Search” box in the upper right corner of the map. Click on the “Themes” layer and toggle on “Zoning”. The legend will indicate which zone or zones your property is located in.  

The Zoning Ordinance outlines the use requirements for each zoning district in Section 10.440 - Table of Uses and the dimensional requirements in Article 5 and Section 10.521 - Table of Dimensional Requirements.  

If you need more assistance with the specific zoning requirements for your project please inquire with the Planning and Sustainability Department staff at (603) 610-7216.

A Land Use Permit Application is required for projects that require land use review by Planning Department staff and those that involve new construction, an addition or expansion of an existing building, home occupations, or any exterior renovations of properties located in the Historic District, as well as for any projects that require approval from the City's land use boards (Planning Board, Historic District Commission, and Zoning Board of Adjustment) including subdivisions, site plan review, conditional use permits, variances, special exceptions, and historic district commission certificates of approval. Please click here for more information on land use applications, forms and fees. For Building Permit requirements see the Inspection Department FAQs.

Please see the following reference guide for fences in the City of Portsmouth here.

The Planning and Sustainability Department (and Portsmouth City Hall) is open Monday 8:00AM - 6:00PM, Tuesday-Thursday 8:00AM - 4:30PM and Friday 8:00AM - 1:00PM. We welcome you to stop by our office on the third floor of City Hall at 1 Junkins Avenue during business hours, call us at 603-610-7216 or email planning@cityofportsmouth.com.