A project of the Solano County Planning Collaborative

Phase One

Getting Started

  • Get inspired
  • Think about your goals
  • Start budgeting


Getting started is part of the Planning phase, which typically takes 1-3 months. Most ADU projects take 12-18 months to complete, but some extend to 24 months or more.


Here are a few of the most frequently asked questions about getting started. See the content below for more guidance, resources, and tips for all steps of the process.

Step by Step

Getting Started

Before you begin Make sure you understand the types of ADUs and the other content covered on ADU 101. You may also want to check out the Glossary to make sure you understand key terms.

Getting Started

Step 1

Think about what you want

Start thinking about your short- and long-term goals and concerns for your ADU project and what kind of ADU is best for your needs. Our ADU Worksheets have a checklist to get you started.

Good sources for inspiration:

Think about what it means to share space with tenants and if that impacts your design and layout. Keep in mind that your plans may change once you hire a professional. Be flexible and open to the possibilities!

Getting Started

Step 2

Consider different types of plans

There are two types of construction to consider for your project. Both have pros and cons, so it can help to think about what you want, like the level of customization you want and how the ADU would work on your specific property (like slopes and obstacles for installation).

Prefab, modular, and panelized are partially or mostly built in a factory, then shipped to your site and assembled or placed on a foundation. Some companies provide a “turnkey” service that helps with permitting and all on-site construction, from laying the foundation to utility hookups. If not, you’ll need to hire additional professionals to help.

Using a prefab design can save time and make clearer what your completed project will look and feel like, but they also typically offer less customization, can be difficult to permit and finance, and often cost the same as site-built ADUs. People are often surprised at the cost, but transportation, crane, foundation, and sales tax can end up being 20-40% of the total cost. Some companies do offer a smaller price point.

To explore prefab or modular ADU options, you will want to get in touch with companies directly. They will visit, evaluate your property, and make recommendations. You can find prefab contractors by researching online.

Site-built is a traditionally constructed ADU built from scratch on your property (AKA “stick-built”). This option allows for a lot of customization and smaller changes to be made throughout the construction process.

Key Resources

Getting Started

Step 3

Make an informal sketch of your property

Make a rough sketch of your property, including the existing home, trees, driveways, large slopes, any other structures, and where you’d like your ADU. Use our ADU Worksheets to help you with this step. (Note: You can update this sketch or make new versions as you continue to learn about your property and what’s possible.)

Key Resources

Getting Started

Step 4

Estimate Project Cost

It’s never too early to plan your project budget. A very rough placeholder to use is $250-350 per square foot, including construction and other costs (design, fees, etc.). The actual number can vary and depends on many factors.

See the Budgeting & Finance page for more information.

Key Resources

Find ADU layouts that fit your needs

Browse real-world ADU layouts from across california

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