Just starting to think about building an accessory dwelling unit (ADU) on your property in San Diego? You probably have a lot of questions…

What is an ADU? Is an ADU the same thing as a companion unit, granny flat, casita, guest house or in-law suite? What and where can I build on my property? How do I start in the process? Do I need to talk to an architect or a contractor first, or maybe start with financing? How much will an ADU cost?

We’re happy to help you get up to speed so you can decide if building an ADU in San Diego is right for you.

ADU 101 Webinar

What is an ADU?

In construction and real estate, ADU means "accessory dwelling unit." The definition of an ADU is a detached or attached dwelling unit that provides complete independent living facilities - including a kitchen and a bath - on the same parcel as a residential dwelling. ADU, granny flat, companion unit, casita, guest house, granny cottage, secondary living unit, mother-in-law apartment, second dwelling unit, in law suite, carriage house, au-pair suite... you may hear any of these terms used interchangeably for an accessory dwelling unit (sometimes mistakenly called an "additional dwelling unit," "auxiliary dwelling unit" or "accessible dwelling unit"... we like to think they're awesome dwelling units).

What kind of properties can have an ADU?

ADUs may be built on residential zoned lots, including single family and multifamily, that have an existing primary dwelling unit on them. Even properties that are in HOAs or the Coastal Zone are eligible to build ADUs.

Single family properties may add an ADU + JADU. Multifamily properties may add two ADUs, plus convert existing non-habitable space into additional ADUs. And in the City of San Diego, you may be able to add even more ADUs under the ADU Bonus Program.

What types of Accessory Dwelling Units are there?

What is a Junior ADU?

Junior ADUs (JADUs) offer an option to add another unit (in addition to an ADU) within your existing home. JADUs must be contained within an existing or proposed single family home (think garage or spare bedroom), under 500sqft (you can add on up to 150 sqft to get to 500), and have a full bathroom and efficiency kitchen (appliances + cabinets).

What about Tiny Homes as ADUs?

Tiny homes have recently been classified as a type of ADU in San Diego – you can have a detached tiny home (150-430 sqft in size, licensed by the DMV) as your ADU in your back yard. Note that this is not in addition to having an ADU; the tiny home is classified as the ADU. Tiny Homes must be connected to all utilities and sit on a concrete pad, which means the all-in costs of using a tiny home for your ADU often end up looking very similar to a permanent ADU.

What are Guest Living Quarters?

ADUs are also sometimes called guest houses, though there is a technical definition of “guest living quarters,” which are different than ADUs. Guest Living Quarters are only for use by those employed on the premises or for temporary use by guests and may not be rented out. Guest Living Quarters may not have kitchens or laundry facilities. In some municipalities, guest living quarters can co-exist with an ADU, but the County of San Diego only allows an ADU or a guest living quarters.

Where can you construct or convert ADUs?

ADUs can take many different forms, either within or attached to your existing residence, or as standalone structures.

New Stand-Alone Unit

Add a standalone detached ADU structure of up to 1200 sqft and up to 24′ tall. Setbacks for the side and rear yard must be at least 4 feet.

Addition or Expansion

Build an ADU as an addition or attached structure of up to 1200 sqft, not to exceed 50% of the floor area of the existing primary dwelling.

Conversion of Space

Convert existing space within the home or garage, up to 50% of the floor area of the main home. Replacement parking isn’t required for garage conversions.

What are the big changes in California ADU regulations?

Size & Setbacks

No minimum lot size requirement for ADUs in CA. ADU size may be up to 1200 sqft, and local municipalities must allow a minimum 850 sqft 1BR or 1000 sqft 2BR+ with only 4′ side and rear setbacks.

Application Review

Building departments have been required to act on any ADU application within 60 days (and we see most acting much sooner). This limit used to be 120 days.


Most parking requirements have been waived (none required if within 1/2 mile from public transit), or are readily addressed (parking spaces may be designated on the driveway).

Owner Occupancy

There is a moratorium on owner-occupancy requirements for ADUs constructed by 2025. Regulations are continuing to evolve towards encouraging ADUs and some cities have dropped owner occupancy requirements indefinitely.


Many impact and development fees for ADUs have been waived, and the remaining fees can be minimized by being aware of the important thresholds for square footage that trigger higher fees.


HOAs (Home Owners Associations) and CC&Rs (Covenants, Conditions & Restrictions) cannot reasonably prohibit development of ADUs. We offer several finish options to readily conform to standards for exterior finishes.

How do I start to build an ADU in San Diego?

With all the moving parts involved with building an ADU, it's tough to know where to start. With an architect? A contractor? Maybe a lender? At the city planning office? Or with an ADU consultant? At Snap ADU by Moore Construction, we're excited to dig into all of these aspects with you and act as the ADU builder and "quarterback" on your project. We have the in-house expertise and established partnerships to guide you through the ADU building process and make it all happen in a snap.

Put simply, we like being involved in all aspects of your ADU project to make sure it goes well, whether you are going full custom or working with a standard plan. We offer our own value-engineered floor plans & designs, but if you have your own architect that's OK, too... or we can also start from scratch with you on designing a custom plan. We also regularly work with the San Diego County Standard ADU Building Plans and the Encinitas PRADU Building Plans (and you'll want to read more about considerations for using county standard plans on our FAQ page). If you will be getting financing, we want to talk to your lender right away to make sure you will have exactly what is required.

How Much Does an ADU Cost in San Diego?

We're so glad you asked! We are big on transparency and like to get into the numbers with you right away. Check out our ADU Costs page with the link below for everything you need to know about the full cost to design, permit & build an ADU in San Diego.

More on ADU Costs

How Long does it take to Build an ADU?

The entire process of designing, permitting, and building a new construction accessory dwelling unit (ADU) will take 10-18 months depending on complexity of your design, the city in which you are located, and your site conditions. Design is roughly 3-4 months, permitting 3-8 months, and build out is 5-7 months (highly variable based on jurisdiction and also unit size). Read more about the three phases and how long each takes.

Time to Build an ADU

Why build an ADU in San Diego?

San Diego homeowners build ADUs for many different reasons. Whether you’re thinking about moving part of your family to the ADU or looking for extra income, ADUs are flexible additions that can afford your family more options on your existing property… while adding value to the property when you eventually sell (or even sooner if you decide to refinance). An August 2020 Bloomberg article mentioned many families are opting for an ADU in the back yard for aging grandparents and skipping the nursing home.

Family Housing

Ready to move your parents onto your property? College students need a place to live? ADUs have you covered for family housing needs.

Rental Income

Rent out your ADU for periods of 30 days or more… or downsize and move into the ADU so you can rent out your main house!

Guest House

Live-in nanny or au pair? Frequent guests visiting from out of town? An ADU can increase flexibility & add to your property value.