Small Homes, Big Potential

Building an Accessory Dwelling Unit (ADU) in Maine

ADU Wizard

The Wizard tool is a starting point to imagine and explore possible options on your property. For the most accurate information, particularly for properties in a shoreland zone, check with your town’s planning staff.

Supporting ADUs Across Maine

Building an Accessory Dwelling Unit (ADU) is an investment in your family, your future, and your community. Whether you’re looking to provide housing for loved ones, earn rental income, or age in place, this guide walks you through each step of the ADU journey in Maine.

The Maine ADU Guide is a collaborative initiative developed by the Greater Portland Council of Governments in partnership, Maine Department of Economic & Community Development municipalities and organizations across Maine. It offers tools, guidance, and inspiration to help Mainers build ADUs in alignment with state law (LD 2003) and local ordinances.

The ADU Process

Explore the step-by-step process to get started with your ADU project today.

Start with these two pages

ADU WIzard

See what’s allowed on your lot

ADU Rules

Learn what you can build

Inspiration

Get started and set goals

Budgeting

Estimate costs and find funds

Design

Hire a team and make designs

Permitting

Refine designs and get permits

Construction

See your ADU come to life!

Watch More About Building an ADU in Maine

Building an ADU is an investment for your family and community

Aging in Place

Keeping loved ones close

Workforce Housing

Rental income

Property value

Caretaker Housing

Downsizing without moving

Environmental Impact

Peace of Mind

Supporting Maine's Housing Goals

FAQs

How much does it cost to build an ADU?

General ADU cost estimates in Maine:

Interior Conversion ADU: $30,000 – $100,000
Garage Conversion ADU: $60,000 – $150,000
Attached New ADU: $100,000 – $300,000
Detached New ADU: $200,000 – $500,000

This cost varies widely based on your design and the requirements of your site and local municipality. See Budgeting for more detailed information on costs and financing for your ADU.

How long does it take to build an ADU?

Building an ADU is an investment of time as well as money. Most projects take 12-24 months to complete, with interior conversions being the fastest.

Planning (learning the rules, setting goals, budgeting): 1-3 months
Design: 1-6 months
Permitting: 1-6 months
Construction: 6-12 months

What do I do first?

This site walks you through each part of the ADU process, from learning the rules and gathering initial inspiration through construction.

We recommend starting with two things:

Use our ADU Wizard by putting in your address and seeing what’s possible.
Read our ADU Rules page and then walk through the pages of this site one-by-one for a detailed guide on what to do next.