The four kinds of ADU
A detached ADU is a new, separate building, usually in the back yard. An attached ADU is new space joined to the house, beside it, behind it or above the garage. A conversion turns space you already have, like a garage or a basement, into a unit with its own entrance. A junior ADU (JADU) is a unit of up to 500 square feet carved out of the house itself.
On a single-family lot, your city must approve one conversion, one JADU and one new detached ADU, all on the same property. These are approved against objective standards only, with no design review hearing, and an HOA cannot block one.
Source: HCD ADU Handbook, March 2026, pp. 16 to 18 and 26How big, and how tall
A city cannot cap an ADU below 850 square feet, or 1,000 square feet for one with more than one bedroom. Whatever else its rules say about lot coverage or floor area, they cannot stop an 800 square foot ADU with 4 foot side and rear setbacks. Where a city has no valid ordinance of its own, a new detached ADU can be up to 1,200 square feet. Since January 2026 these limits are measured as interior livable space.
A detached ADU can be at least 16 feet tall, and 18 feet near major transit, plus 2 more for a roof that matches the house. An attached ADU can reach 25 feet, or the height limit for the house if that is lower. Side and rear setbacks can be no more than 4 feet, and a conversion or a garage rebuilt on its own footprint needs none.
Source: HCD ADU Handbook, March 2026, pp. 24, 25 and 37 to 39Parking
Often none. A city cannot require parking for an ADU within half a mile's walk of public transit, and a regular bus stop counts. Conversions and the by-right units above need no parking at all. If you convert or demolish a garage to build the ADU, the city cannot make you replace those spaces, covered or not.
Source: HCD ADU Handbook, March 2026, pp. 33 and 34How long the permit takes
Once you apply, the city has 15 business days to tell you whether the application is complete, or it is treated as complete. It then has 60 days to approve or deny a complete application, or the ADU is deemed approved. A denial has to come with written comments explaining what to fix, and since 2026 every city must offer an appeal.
Every city also has to offer pre-approved ADU plans. A detached ADU built from one must get a decision within 30 days.
Source: HCD ADU Handbook, March 2026, pp. 34 to 36 and 50Fees
There are no impact fees on an ADU of 750 square feet or less. Above that, they are charged in proportion to the size of your house, so a 1,000 square foot ADU behind a 2,000 square foot home pays about half of what a new house would. School districts may charge fees on an ADU over 500 square feet. In most cases a conversion cannot be made to take a new utility connection or pay a connection fee.
Source: HCD ADU Handbook, March 2026, pp. 22 and 23Renting it out, and selling it
You can rent an ADU, and no city can require you to live on the property to do so. Cities can prohibit short-term rentals of 30 days or less, and the by-right units and JADUs cannot be short-term rentals at all. A JADU that shares the house's bathroom does require the owner to live in one of the two.
Selling an ADU separately from the house is only possible where the city has adopted an ordinance allowing it, and every lender on the property has to agree. We have not found a San Gabriel Valley city that has, so ask yours before planning on it.
Source: HCD ADU Handbook, March 2026, pp. 32, 33 and 36Already have an unpermitted unit?
If it was built before January 1, 2020, California lets you legalize it. The city cannot refuse the permit over building code or zoning problems unless fixing them is necessary for health and safety, and it cannot penalize you for having had the unit. Before you apply, you can have a licensed contractor do a confidential inspection, so you know what needs fixing before the city sees it. That is something we do.
Source: HCD ADU Handbook, March 2026, pp. 35 and 41Coming in 2027
Two ADU bills were signed in September 2026 and take effect on January 1, 2027. AB 956 gives single-family lots more flexibility in which kinds of ADU can be built by right, including a second detached unit in some cases. SB 1117 changes how impact fees are worked out for some ADUs over 750 square feet. Neither is in force yet, and we will update this guide when they are.
Source: Office of the Governor, September 29, 2026Rebuilding after the Eaton fire
If your home in Altadena or Kinneloa Mesa was damaged or destroyed, the rules are more generous. You can build the ADU first and move into it before the house is rebuilt: the state allows that through January 16, 2028, and LA County lets a family live in an ADU on a lot with no house until January 7, 2030. The County's Eaton fire interim ordinance, now extended to August 22, 2027, lets a like-for-like rebuild add ADUs and drops replacement parking where the ADU sits on the footprint of a garage that burned. The County also publishes pre-approved plans for fire rebuilds.