ADU eligibility is a common question due to limitations to California's new regulations. Learn about local regulations and their effect on ADU construction.
Updated May 06, 2021
Before building an ADU of any kind, one of the first questions to answer is 'Am I eligible to build the ADU that I want in my backyard or garage space?'
Newly passed 2020 California regulations require municipalities to ministerially approve ADUs that meet a certain set of criteria, ignoring any restrictions on lot coverage, floor area ratio, open space, or minimum lot size. However, there are certain limitations to those regulations that we cover below.
There is one key exception: If you are planning to convert an existing garage or accessory structure into an ADU (either by using the existing building or demolishing and building from the ground up), your ADU can be built within the existing setback even if it is within four feet of the property line. This assumes, however, that the structure is legal in the eyes of the city; illegally built accessory structures, sheds, and garages do not count.
One additional setback requirement to note: most cities and counties require a minimum distance between any new detached ADU construction and the existing home. While most cities have a six (6) foot existing structure setback requirement for detached ADUs, others have up to ten (10) foot requirements.
While these setbacks can limit the space you can build your new backyard home, they provide some simple rules of thumb for determining your eligible ADU locations.
ADU Size and Height
It is worth noting that while the new AB 68 regulations simplified the ADU process considerably, there are still some base requirements to be able to qualify as a California Statewide Exemption Accessory Dwelling Unit and qualify for ministerial approval. However, most cities and counties have also made it easier to build larger ADUs, with some restrictions.
In terms of size, the California Statewide Exemption ADU regulation requires that the ADU be below 800 sq. ft in footprint, and below 16ft in height. In addition, it must still meet building code and health and safety requirements, per the definition of an ADU.
Cities and municipalities can and do allow for larger structures, but these regulations vary from city to city and county to county. For example, San Jose allows for detached ADUs to be built up to 1,000 sq. ft on lots less than 9,000 sq. ft., and up to 1,200 sq. ft for lots 9,000 sq. ft and greater. For its part, San Jose has also loosened some restrictions further; for example, you can build up to 18ft for a one-story detached ADU, and 24 ft. for two-story detached ADUs, with some exceptions.
In Redwood City, for example, attached ADUs may not exceed 50% of the existing living area if the unit is planned to be greater than 800 sq. ft, and detached ADUs up to 1,000 sq. ft are allowed on RH and R-1 zoned lots of at least 10,000 total sq. ft. However, the city also has an 850 sq. ft maximum for 1 bedroom ADUs; anything larger requires an additional bedroom space. In terms of minimum size, Redwood City is like many other Bay Area cities that requires at least 150 sq. ft for new ADU construction.
As you can see, there is considerable variation in local ADU regulations beyond the California Statewide Exemption ADU policy that applies across the state. Cottage specializes in ADU eligibility and the start-to-finish custom ADU process - contact us at the link below to learn more.
ADU Replacement Parking
With the recent changes from Assembly Bill 68 in the state, homeowners no longer have to replace parking for garage conversion ADUs. In addition, the regulation removes the parking spot requirement for all accessory dwelling units built with half a mile from public transportation. In some areas like Piedmont, that rules out the need for replacement parking across the entire city.
For the majority of homeowners that Cottage has worked with, living near a local bus, train, or carpooling area has eliminated the need for adding parking for your ADU.
How Many ADUs?
Thanks to the updated California regulations, single family homeowners are now allowed to build both a regular detached ADU as well as a Junior ADU. As we covered in our ADU types post here, a junior ADU is an ADU that is a portion of an existing building that is converted into a separate living space. An extra bedroom, bathroom, and kitchen partitioned off from the existing house is one way we've seen that work for homeowners, and a converted garage is another.
Be careful though—many cities and counties have owner-occupancy requirements for junior ADUs that require you to live in at least one of the units or existing home if you classify one of the units as a junior ADU. This limits your rental income potential from more than 2 units at a time.
If you own a multi-family home or home that is zoned as a multi-family lot, you are entitled to build up to two ADUs on the property. Floor area, lot coverage, and open space requirements from the specific municipality or county may apply, however. We have worked with homeowners such as Harmol here to build multiple ADUs on their multi-family property in the past.
What ADU is right for me?
There are a few key things to think about when proceeding with your ADU project, and Cottage is here to help every step of the way. Contact us today using the link below for a Free, No-obligation Consultation & Estimate with one of our ADU experts!