Learning the Rules

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!

Some jurisdictions provide a courtesy notice about a project to the surrounding properties.

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.

In almost all cases, yes! ADUs and JADUs are allowed in any single-family or multi-family zone. If residential buildings are allowed, ADUs are almost always allowed too (with limited exceptions for safety, traffic, and water).

State law now allows a single-family property to have multiple ADUs, and some communities allow even more. Confirm with your local staff before planning multiple ADUs. Multifamily properties ­– like duplexes, triplexes, and apartment buildings – can have two detached ADUs or up to 25 percent of the number of units, depending on your property. Talk to Staff for more information if interested in building ADUs on a multifamily property. Developers building new homes or multi-family housing can include ADUs at the same time – confirm with staff.

Homeowners can convert legally built structures (garage, barn, art studio, etc.) into an ADU or JADU. JADUs can be converted from an attached garage (but not detached). Check out this extensive guide to garage conversion ADUs from the Casita Coalition.

You do not need to replace the parking space if converting the garage to an ADU, but you may need to replace it if converting to a JADU – confirm with local staff. Demolition permits for an existing detached garage can be processed at the same time as the ADU permits. Note that garage conversion ADUs may require significant moisture barriers and other design elements in order to meet building codes.

Generally, ADUs can range from 150-square-foot efficiency units up to 1,000 square feet. Junior ADUs (JADUs) can be up to 500 square feet. See Local ADU Rules for more details on height, setbacks, and other rules and our Guidebook for more detailed information about important ADU laws.

According to state law, you can at least build up to an 800 square feet ADU, as long as rear and side setbacks are at least 4 feet and it is not above 16 feet tall. In these cases, local regulations like lot coverage, floor area, and some others do not apply. Otherwise, size limits depend on your property and your community’s rules.

According to state law, rules about setbacks, lot coverage, and open space requirements cannot restrict you from building an 800 square foot ADU, as long as the ADU has setbacks of at least 4 feet and is not above 16 feet tall. Front setbacks also cannot restrict you from building an 800 square foot ADU, which means an ADU can be in a front yard – but only if rear or side placement isn’t possible.

Multifamily properties ­– like duplexes, triplexes, and apartment buildings – can have multiple ADUs, but no JADUs. Talk to Staff for more information if interested in building ADUs on a multifamily property. Developers building new homes or multi-family housing can include ADUs at the same time – confirm with staff.

JADU owners need to live in the primary unit or the JADU – and this will need to be recorded in a deed restriction for the property.

Owner occupancy is not required for ADUs.

Parking is much less of a concern than it used to be. JADUs do not require a new parking spot. Check Local ADU Rules to see what parking may be required in your location.

No parking is required if it is:

1. Within ½ mile walking distance to transit (including a ferry);
2. Within an architecturally or historically significant district;
3. On-street parking permits are required and not provided to the occupant of the ADU;
4. Located within one block of car-share access, or
5. Built as part of a new home project.

In most cases, if the main house doesn’t have fire sprinklers, then the ADU/JADU won’t be required to install sprinklers. However, there are some exceptions to that rule where sprinklers may be required:

• If you build an ADU larger than 50% of the main house
• If you build over a garage
• If the ADU is farther than a certain distance from the street (typically 150′) or closest fire hydrant (typically 400′)

Check with your local Planning Department and Fire Marshall for exact details once you’ve developed your project further.

Utility connections can have significant design and scheduling impacts, so it’s good to think about them early on.

In general, it is less expensive to hook the ADU utilities to the main house, as opposed to building new water and sewer laterals to the mains in the street, or a second set of electrical lines from the pole. In some cases, particularly if your ADU is larger, over 750 sf, you may be required to construct new connections. It is best to discuss this issue with your jurisdiction early in the design process.

Most homes will need to upgrade the main electrical panel and possibly electrical service to the property. This will involve both an electrician as well as coordinating with PG&E. Due to the demands on PG&E services, the upgrade process can take significant time and homeowners are often charged a $1,500 engineering fee for PG&E to begin the process. Additional fees may be charged depending on the condition and size of the electrical components running to the property.

Typical utility upgrades for an ADU include a main electrical panel of at least 200 Amps and a sewer lateral of 4″ for the whole property. If the existing lateral is 3″ you may have to replace it with a 4″ lateral to the street to handle the additional demand created by the ADU. Please consult with your building department for more information.

Water service may need to be upgraded as well, particularly when sprinklers are required such as when an ADU is built above a garage. The scale and cost of this work depends greatly on the age of the main house and the infrastructure provided by jurisdiction. It is important to determine if sprinklers will need to be planned for and get information on the water supply to your property early in the design and bidding process. This information is typically available from your Public Works or Engineering Department.