- Clarify what you want
- Get inspired by other ADUs
- Estimate project cost
GETTING STARTED with an ADU project is what many feel is “the fun part” – you’ll think about your goals and the value an ADU will bring, look for design and layout inspiration, and start to figure out what will work on your property.
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.
for Getting Started
Frequently Asked Questions
Here are a few of the most frequently asked questions about getting started. See the content below and your County’s ADU Guidebook for more guidance, resources, and tips for all steps of the process.
Building an ADU is an investment of time as well as money. Most projects take one to two years to complete. Typically, it takes homeowners one to three months to get started and assemble their team, then one to six months to develop plans, meet with the city, and submit the application. Depending on what permits are required, how many rounds of review are required and how quickly a homeowner and their project team can respond to comments, it will take one to six months to get permits. Construction usually takes six to twelve months.
You’re not required to tell your neighbors about your ADU, but it’s always a good idea to communicate with them early in the process. Your project will run more smoothly if they are kept informed, and they may have great ideas for your project!
If you live in a Neighborhood or Homeowners Association, talk with your representative or board early in the process. They can’t prevent you from building or renting an ADU, but they may have guidelines you’ll need to know for design and construction. Depending on where you live, written approval from your HOA may be required before your location will permit your ADU.
ADUs often need separate waste treatment and your system may need to be modified. Contact your Environmental Health Department early in the process. For contact information, see the Contact page.
ADUs may require a well report and well systems may need to be upgraded. Contact your County Environmental Health Department early in the process. For contact information, see the Contact page.
The best place to start is with thinking about what you want, understanding your goals and concerns, and looking at other ADUs for inspiration. Once you have some ideas in mind, you can consider your budget and move on to Learning the Rules to figure out what you can build on your property.
You can also use your County Process-at-a-Glance resource for an overview of the steps and some initial issues to consider as you get started.
To see translated Spanish FAQs, head to All FAQs.
Getting Started, Step-by-Step
Getting Started Step 1
Think About What You Want
Start by 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 Exercises have a checklist to get you started. Talk to friends and neighbors who have built an ADU and reach out to any builders or designers you know for a casual chat. Check out our ADU Stories, sample floorplans, and ADU Plans Gallery for inspiration.
Keep in mind your plans might change once you hire a professional. On a more personal note, it’s a good idea to notify your neighbors about your project (not required but recommended), and to think about what it means to share space with tenants (and if that impacts your design and layout).
Getting Started Step 2
Make an informal sketch
Make a rough sketch of your property, including the existing home, any other structures, and space for a possible ADU. Use our ADU Exercises 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.)
Getting Started Step 3
Estimate Project Cost
It’s never too early to start thinking about and planning for your project budget. Costs differ across the region, but a very rough placeholder for you to start from is $300 per square foot, including construction and other costs (design, fees, etc.). The real number can vary widely and depends on many factors. Our County ADU Calculators are a great place to start when developing a budget. Each one provides a rough estimate of costs and income and will help you understand how choices can impact your budget over time, all customized to real local numbers.