A project of the Solano County Planning Collaborative

Phase Two

Learning the Rules

  • Understand the rules and regulations for your community
  • Learn what you can build on your property


Learning the Rules 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 ADU rules.

Questions about Special Zones

Step by Step

Learn the Rules

Keep in mindUnderstanding how local and state rules apply to your project can feel like a lot at first.  Remember: City or County staff are here to help. See our Contact page for more details.

Learning the Rules

Step 1

Learn about your property

First, confirm what City or County your property is in and gather some basic information about your property:

  • Assessor’s Parcel Number (APN)
  • Lot size
  • Neighborhood zone
  • Special zones: Flood zone, seismic zone, snow load, fire districts, and more. 

You may also want to verify your property lines – You may think your property ends at a fence or driveway, but these may have shifted over the years. Ask City or County staff the best way to confirm this information or contact your County Assessor & Recorder’s Office for a recorded map. If still needed for your project, consider hiring a surveyor for a detailed map of your property.

Use our ADU worksheets to take notes on all the details you’ll need.

Learning the Rules

Step 2

Learn what you can build

Next, you’ll need to understand what you can build on your property. Local and state laws will impact what is possible for your ADU, like its size and height and may include additional  requirements about parking, fire safety, and more. 

Below is a summary of state laws, but these may vary based on your location and property. Please speak with City or County staff to confirm.

Almost all residential properties are allowed to add ADUs and/or JADUs. Single-family properties can build both an ADU and a JADU, and multi-family properties can usually add multiple ADUs (but no JADUs). ADUs can also be built at the same time as new housing. 

Note that all ADUs and JADUs must have their own external entry. JADUs must also have an interior entrance if sharing a bathroom with the main home.

  • JADU: Maximum 500 square feet
  • Detached ADU: At least 850 square feet (1 bd) and 1,000 square feet (2 bd)
  • Attached ADU: At least 800 square feet or up to 50% of primary home square footage
  • Conversion ADU: No requirement but limited to existing size – adding up to 150 SF of new square footage is allowed if needed for ingress or egress.
  • Attached and Conversion ADUs: Up to 25 feet or height allowed by underlying zoning, whichever is less
  • Detached ADUs within ½ mile of public transit: Up to 8 feet plus 2 feet for roof pitch (allows for two-story ADU)
  • Multifamily: Up to 18 ft (allows for two-story ADU)
  • All other ADUs: 16 ft

Setbacks are the distance from your property boundary to the main home or ADU.

Attached/detached ADUs:

  • New Construction: 4 feet side and rear setbacks
  • Conversions: No change in existing setbacks required

Note: According to state law, you can build up to an 800 square foot ADU, as long as rear and side setbacks are at least 4 feet and it is not above 16 feet tall. No room behind or next to your main home? You can build it in your front yard instead.

Key Resources

Learning the Rules

Step 3

Meet with staff

One of the best things you can do is to talk to City or County staff early in the process about potential issues and rules that might apply.

Use our Worksheets to help plan your conversation and take notes.This is also a good time to contact any utility service providers (waste, sewer, gas, electricity, etc.) to confirm requirements, timelines, and fees. See our Contact page for more details.

If your basic project details (size, number of bedrooms) change based on this meeting, it’s a good idea to adjust your estimated project budget.

Not sure what questions to ask?

Check out our ADU worksheets

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