What Is Considered an ADU in California?

Accessory dwelling units (ADUs) are known by many names — granny flats, coach houses, ohana units, backyard bungalows, and alley flats — but it can be challenging to find a definitive answer as to what characterizes an ADU. If you’re considering adding an ADU to your property, understanding what you’re getting into is the first, often overlooked, yet critical step in a lengthy process.

Below, take a deep dive into what separates an ADU from other types of home construction to determine if adding one to your property is right for you.

California defines an ADU as an attached or detached residential dwelling unit that provides complete independent living facilities for one or more persons and is located on a lot with a proposed or existing primary residence. They must include permanent provisions for living, sleeping, eating, cooking, and sanitation on the same parcel as the primary dwelling. AARP contextualizes that definition to characterize ADUs as self-contained living spaces of various types.

Additional official ADU features are often established and governed by city zoning and development entities, so be sure to check with your local planning department for the most accurate and updated information.

Homeowners must permit ADUs before construction begins and comply with local regulations. Various types of ADUs exist, with a multitude of exterior and interior features dictated by how homeowners intend to use the extra space.

Similar to the process of building an ADU in your backyard, visualizing the design and layout can help give it shape.

Below are the key characteristics of an ADU in California:

Based on their small footprint, ADUs are often confused with tiny homes. Although they share the concept of a compact living space, ADUs require a foundation and permitting, while tiny homes tend to be more mobile. Landowners can also place a tiny home on a designated parcel, while ADUs typically exist as an addition to a primary residence.

Several types of ADUs exist, including detached, attached, and converted. Detached ADUs are often the easiest to spot because they are separate from the primary residence. In comparison to the main house, a detached ADU is a self-contained, self-sufficient dwelling with its own living spaces, bathroom(s), and kitchen.

Attached ADUs share part of the existing structure with the main house but require additional construction, similar to an add-on or home addition. Most attached and converted ADUs have a separate entrance so occupants can come and go as they please. Homeowners typically convert garages, storage rooms, basements, and attics to ADUs.

Like single-family residences and multi-family dwellings, ADUs require a lot that’s zoned for residential rather than commercial or industrial use. However, you can typically find ADUs in rural and urban areas in California, from big cities like Los Angeles and San Francisco to the small suburbs of Laguna Beach or Santa Barbara.

As long as an ADU complies with local zoning and building codes and is permitted by the governing city, it can legally exist in almost any type of environment.

Similarly, owner occupancy isn’t required in all Californian jurisdictions, allowing homeowners to build an ADU on property they’re currently renting but don’t use as their primary residence. In addition, multi-family dwelling property owners can build at least one conversion ADU and up to two detached ADUs on a single plot if permissible.

On lots with existing multi-family dwellings, property owners can convert non-livable space into ADUs. The number of ADUs created cannot exceed 25% of the total number of existing dwelling units.

Homeowners can also distinguish ADUs based on their intended use. At the core of California ADUs lies a need for affordable housing in a state with a high cost of living.

Here are a few ways homeowners put their ADUs to use:

According to AB 1033, homeowners can build and sell ADUs as condominiums under certain circumstances. However, most ADUs must remain with the primary residence when bought or sold.

Building an ADU legally, regardless of the type of ADU you select, requires a permit from your local city planning and development department. Homeowners can choose to obtain permits themselves or leave the permitting process up to a general contractor or licensed ADU builder.

Even if you purchase a prefabricated ADU, you must still obtain a permit to install it on your property. In California, permitting agencies have up to 60 days to approve or deny an ADU permit application once a complete application has been submitted.

Should the city planning department reject your ADU permit application, they must provide you with detailed reasons for the denial and a solution for fixing those errors or making the appropriate corrections. Each city has the authority to establish and enforce ADU permitting fees, including impact fees.

If you’ve done any research on ADUs, chances are you’ve come across the acronym JADU. Otherwise known as a junior accessory dwelling unit, JADUs are restricted to 500 square feet or less and must be constructed within the confines of an existing single-family residence.

A JADU doesn’t expand the expected occupancy of the home, and construction costs often total much less than a traditional ADU. In contrast to ADUs, a JADU cannot be bought or sold separately from the house.

However, homeowners can still rent out the space or use it to house a college student or aging loved one. Many may find this arrangement more amicable than a nursing home or off-campus apartment, as the JADU can share a bathroom and many central systems with the primary residence while still maintaining a separate living space.

Many homeowners use cash-out refinancing, construction or renovation loans, home equity loans, or home equity lines of credit to fund their ADU projects. However, Samara offers homeowners a welcome alternative: financing that doesn’t require swapping their current mortgage payment — and, more importantly, low interest rate — for a costlier loan.

Instead, Samara financing provides homeowners with APRs as low as 6.5% with as little as no money down and no payments or interest for the first six months.

Samara takes the guesswork out of designing, building, and enjoying an ADU with five expertly prefabricated Backyard ADU floor plans to choose from. Homeowners benefit from a proven, straightforward process that spans seven months, including permitting.

Samara’s efficient supply chain and experienced team turn 30 days of on-site labor into a move-in-ready ADU homeowners can enjoy however and whenever they please.

Schedule a 15-minute call with a Samara specialist to learn more about our Backyard ADU and how incorporating it into your property can benefit you. Our specialists are also available at 650-420-2607 to answer any questions. Samara also works with developers to maximize available space and offer affordable housing.

Samara’s efficient supply chain and experienced team turn 30 days of on-site labor into a move-in-ready ADU homeowners can enjoy however and whenever they please.

Schedule a 15-minute call with a Samara specialist to learn more about our Backyard ADU and how incorporating it into your property can benefit you. Our specialists are also available at 650-420-2607 to answer any questions. Samara also works with developers and hospitality providers to add high-quality, prefab housing to properties.

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