Design

Overview

Identify what you want in a design
Understand the design process and professionals involved
Hire a professional team to create your design

Once you have a sense of what you want to build, know what you can build, and have estimated your budget, you can start designing your ADU, which begins with design inspiration and ends with permit-ready plans.

Project Timeline

The Design phase typically takes 1-6 months. Most ADU projects take 12-18 months to complete, but some extend to 24 months or more.

FAQs

When do I show my designs to local staff?

Once you have a design established with your architect/designer, it’s a great idea to discuss it with Planning staff so they can point out any issues before you prepare your application.

How do I find an architect or designer?

Most homeowners choose to work with some type of design professional to plan their ADU and help throughout the process. Bringing on a professional early in the process is often key to getting your ADU approved quickly, managed efficiently, and built cost-effectively. Relevant experience and fit will be critical.

There are a variety of types of designer, and they may be an architect, builder, “designer,” design/build, or a modular/prefab company. If you’re hiring a local individual or team, they’ll likely start the process by visiting your home and talking to you about your ideas and goals. If it seems like a good match, they will prepare a proposal detailing their services and fee. Professionals typically charge for an initial consultation or proposal.

Check our professionals directory to see if there’s a good fit for your project.

What’s the difference between a site-built and a prefabricated or manufactured ADU?

There are two types of construction to consider and both have pros and cons, so think about the level of customization you want and how the ADU will work on your property.

Site-built ADUs

Traditionally constructed and built from scratch on your property (AKA “stick-built”), which often slows for a lot of customization and smaller changes throughout construction.

Typical benefits:

More options for customization
Can be easier to get financing and permits
Can be easier to place on unique properties (steep slopes, rocky terrain, small spaces)
Can typically be paid for phase-by-phase

Prefab, modular, and panelized ADUs

Built in a factory, then shipped to your site and assembled or placed on a foundation. Some companies provide “turnkey” service with support through the entire process (permitting, construction, etc.). If not, you’ll need to hire other professionals to help.

Prefab ADUs are categorized based on how they are built and inspected.

Partially-fabricated (panelized, framing kits) Parts of the ADU are built off site at a factory, and construction follows a traditional site-built pattern. Local inspectors check work at different stages and a local general contractor and their crew are responsible for putting all the pieces together and passing inspections.
Prefabricated (modular, manufactured, factory-built) The ADU is built and inspected for building code off site at a factory, then delivered and put in place on your property by a crane or tow. Local inspectors only check work like foundation and utility hook-ups. These types are all built similarly but are called different things based on what building code they meet (state, federal, etc.).

It’s important to note that prefab ADUs may cost the same as site-built ADUs – transportation, crane, foundation, and sales tax can end up being 20-40% of the total cost. When you get in touch with prefab companies, be sure to ask what is included in the price. Some companies do offer a lower price point.

Typical benefits:

Lower design and engineering costs
More clarity on what you’ll get in the end
Faster construction with less on-site disruption
Quality inspections from the start
Fewer permits and inspections

Design, Step-by-Step

Before you begin It is helpful to have a clear sense of what you want early in the process. An architect or designer can help you brainstorm, but they cannot start designing until you’ve made basic decisions like the type of ADU you want (see the inspiration page) and how many bedrooms it will have.

Step 1

Hire Experienced Professionals

Find a Maine-based architect, designer, or design/build firm with ADU experience.

Looking for a designer or prefab company? Check our Professionals Directory.

Although you can build an ADU as an owner builder, we strongly recommend hiring a licensed architect or designer and a licensed contractor, or a design/build team, and most homeowners do. Bringing on a professional early in the process is often key to getting your ADU approved quickly, managed efficiently, and built cost-effectively. Relevant experience and fit are critical, and it’s important to look at their past work and check references.

Based on the type of ADU and details of your project, your team may include one or more of the following:

Licensed architect or designer to design your ADU and potentially see you through permitting and construction
Engineers and specialty consultants (examples: septic consultant, landscape architect)
Licensed contractor to build your ADU
Design/build company that designs and builds your ADU
Modular/prefab company who sells preset designs for modular/prefab homes

Step 2

Create Initial Design

Once you have your team in place, you will work with them to design your ADU.

Key Considerations:

Size, orientation, and style
Accessibility and energy efficiency
Historic or coastal design requirements (if applicable)

First, your designer will take measurements of your property (and/or ask you to hire a surveyor to complete detailed, accurate technical drawings of your property) and create conceptual drawings including the potential ADU and its relationship to the main house and other features. They will then lead you through a decision-making process to confirm a main concept (size, orientation, etc.) and start making more detailed plans.

Once you have an initial design, it’s a good idea to discuss it with local staff so they can point out any issues before submitting your permit application. Your design team can attend this meeting to clarify drawings and help you understand requirements.

If you haven’t already, this is also a good time to reach out to utility service providers (water, sewer, gas, etc.) to confirm your design meets their requirements.

Step 3

Finalize Your Design

After you’ve made decisions about your initial designs and received feedback from local staff, your design team will work through any required changes and prepare the permit application (see the permitting page).

At this point you can also get construction drawings from your designer that you could use to get construction bids from potential contractors.