How large can ADUs/JADUs be? What are the required setbacks?

ADUs can range from 150 to up to 1,200 square feet except for lots zoned Agricultural Exclusive (AE) that are 40 acres or more where an ADU unrestricted in size may be allowed in addition to a main residence. You can also build an ADU larger than 1,200 square feet with a Special Permit. ADUs fall into three categories:

Detached ADUs can be up to 1,200 square feet if it fits on your property. They can be up to 16 feet tall (or 26 feet tall on larger residentially zoned lots) and if it’s a new structure, it must have at least 4-foot side and rear yard setbacks. Setbacks do not apply to an ADU converted from a freestanding structure.

Attached ADUs can be up to 50% the size of our existing primary house, OR 1,200 square feet – whichever is smaller. So, if your home is 2,000 square feet, you can build a 1,000 foot attached ADU. Even if your house is huge, your attached ADU cannot be larger than 1,200 square feet without a Special Permit. When doing calculations, do not include your garage, sheds, or storage areas and ask the county if they have an official record of your existing floor area or what spaces to include. An attached ADU can be new or converted from an interior space as long as it shares at least one wall with the primary house.

Junior ADUs (JADUs) can be up to 500 square feet of converted space in a single-family home and must include an efficiency kitchen (sink, stove, fridge, and counter). Some JADUs have their own bathroom, while others share one with the main house. State law now allows homeowners to have both a JADU and a regular ADU on their property. Construction costs for JADUs are typically much lower.