If you’ve got that space, you’re off to a good start. But there are a number of other property size requirements, as well. United Dwelling focuses on detached ADUs, but it’s worth noting an ADU that’s attached to an existing home can only be 50% of the size of the main unit. 

For example, if a home is 2000 square feet, the attached ADU can max out at 1000 square feet.

On the other hand, a detached ADU can be up to 1200 square feet, no matter the size of the main building.

Generally speaking, an ADU has to be less than 16 feet tall. And if your ADU is below that 16 foot height and is under 750 square feet, its building permits can’t be blocked.

If you’re building an ADU within a home or existing building, the ADU can max out at the maximum height of the existing structure.

There are also requirements for minimum interior space and how it breaks down — unfortunately, if you were planning on building one giant bathroom in your ADU, you’re going to have to adjust your plans. The living room/bedroom needs to be at least 70 square feet.

The kitchen (along with the hallways and closet) must measure in at 50 square feet.The bathroom must be at least 30 square feet and contain a toilet, sink, and a shower stall or tub.

The size of your ADU is important, but just as crucial are the materials you use to build it. There are critical standards to ensure that granny flats represent high quality housing options. 

There are any number of exterior cladding options, but a few are against regulations. Builders may not use single piece composite, laminates, or interlocked metal sheathing. As for the roof, it can’t be made of wooden shingles. It must also have a minimum of a 2:12 pitch for greater than 50 percent of the roof area. 

Windows, meanwhile, must be at least double-pane glass and labelled for building use, and they can’t have exterior trim.

Thanks to AB 68, homeowners that turn their garages into ADUs (or knock the garage down to build an ADU from scratch) no longer have to replace the lost parking spaces.

Additionally, there is now no parking spot requirement at all for units built within half a mile from public transportation. Around LA, it’s rare that some place isn’t within a half mile of some kind of public transport.

You also don’t need a parking spot if you’re in a historic district.

According to California granny flat law, owners of single-family homes can now build both a regular detached ADU as well as a smaller unit that’s known as a Junior ADU.

A Junior ADU is a smaller ADU that is part of an existing main building; it can extend the building up to 150 square ft. feet beyond the original footprint of the house. In many cases, a junior ADU is a remodeled extra large bedroom or garage that includes its own bathroom and some kitchen appliances.

If you own a multi-family home, you can build two full-size ADUs on the property (provided you have the space for it, of course).