skip to Main Content
Accessory Dwelling Units In California: Frequently Asked Questions

Accessory Dwelling Units in California: Frequently Asked Questions

The signing into law of AB 68, AB 881, and SB 13 in 2019 has sparked a wave of interest in accessory dwelling units (ADUs) as a potential solution to the California housing crisis. At Edrington and Associates, we have helped dozens of Bay Area property owners assess the feasibility of adding or legalizing an ADU on their properties. If you are considering adding an ADU to your property, you probably have many questions already. The following guide provides answers to some of the most common questions we get from prospective clients.

Why build an ADU?

The primary reason most homeowners decide to build an ADU is to increase the value of their property and/or generate passive income through the rental market. An ADU can also serve as a place of residence for elderly family members or loved ones. ADUs are particularly attractive in markets like the San Francisco Bay Area where available housing is in short supply, and in some cases they help create more affordable housing that can help mitigate the ongoing housing crisis in California.

Make Your ADU a Reality:


What are the different types of ADUs available? 

The three main varieties of ADUs are attached, detached, or conversion units. The attached ADUs are for single-family properties only and must be built attached to the primary dwelling. A detached ADU is a separate stand-alone structure from the primary structure, such as a cottage, and can be added to both single-family and multi-family properties.  A conversion ADU is created from converting existing space into a separate unit. For single-family properties, this can be any existing space. For multi-family properties, only existing non-livable space (such as storage, garages, or basements) may be converted to an ADU. Whether an attached, detached, or conversion ADU, each unit must have a separate entrance, kitchen, bathroom and sleeping facilities.


I own a single-family home.  Can I add two ADUs?

Potentially, but there are some caveats. State law allows for one ADU plus one Junior ADU (JADU) per single-family lot, however, adding a JADU requires owner-occupancy of either the JADU or the primary dwelling. Furthermore, JADUs can only be created by converting space within the existing walls of a single-family residence (including attached garages), which is not an option on all properties.

What is a Junior ADU?

Junior Accessory Dwelling Units (JADUs) are a special type of conversion ADU created within the existing walls of a single-family dwelling, and with a maximum size of 500 sq.ft. JADUs can share bathing facilities with the primary dwelling, in which case the actual square footage of the unit can be as small as 150 sq.ft. Practically speaking, this is usually not desirable from either a size or privacy standpoint. With its own bathroom, the minimum size for a JADU is 220 sq.ft. JADUs also require owner occupancy of either the JADU or the primary dwelling. A JADU and a standard ADU can both potentially be added to the same lot, depending on space.

Can I convert my garage that sits on the property line to an ADU?

Yes, if it is a legal structure. However, it must meet current building and fire codes since it will be considered a change in use.

Can I convert my basement to an ADU?

Yes, you can convert your basement to an ADU or a Junior ADU. You must meet the building code, which includes adequate ceiling heights and minimum sizes on windows for ingress and egress.

Code enforcement has cited me for an illegal unit.  What can I do?

Most jurisdictions will require you to either convert the space back to the original permitted use or convert the space to habitable space. With the new ADU laws, many property owners now have a path to legalizing such units that didn’t exist in the past. If you have a current tenant, we recommend that you consult legal counsel to help you legally relocate the tenant first.

I have a non-permitted unit that I believe was built to building code.  How do I legalize it?

Your unit may qualify for an amnesty program if there are no Health and Safety Violations and such a program exists within your jurisdiction. Depending on when the unit was constructed, it may only have to meet the building codes from that era, not all current code requirements. Even without a formal amnesty program, it may be possible to legalize the unit through the ADU process.

I own a single-family home in a homeowner’s association.  Can I add an ADU?

Yes. Homeowners associations must allow ADUs and have a reasonable design review process. Property owners who encounter issues with their HOA are encouraged to contact the California Department of Housing and Community Development.

Am I required to provide parking spaces for residents of an ADU?

Generally speaking, no, you are not required to provide parking spaces for an ADU, provided that public transportation is available within half a mile of the residence. Parking spaces for an ADU may be street parking, tandem driveway parking and may not exceed one space per unit or bedroom.

Can I add ADUs to my multi-family building?

Yes, you can add at least one ADU and potentially add multiple ADUs depending on the number of existing units. If you have space in your building that is not currently used as livable space (such as storage, parking, etc.), you can add one conversion ADU in such space for every 4 existing units. Properties with fewer than 4 units can add one such ADU. Furthermore, building up to 2 new detached ADUs is also an option. Depending on your local jurisdiction, it may even be possible to combine these options, getting both the conversion and detached ADUs added to your lot.

Do new ADUs added to an existing multi-family building have to provide disability access?

For buildings with three or more units, certain ADUs will be subject to accessibility requirements. For these buildings especially, it is important that you work with a licensed architect to design your unit and its accessible features.

What are the ADU size limits

In absence of any local limits, California state law limits ADU size to 1,200 sq.ft.  However, even with local limits, local jurisdictions must allow up to 850 sq.ft. for a studio/one-bedroom and up to 1,000 sq.ft. for a 2-bedroom ADU.  A new ADU built attached to a single-family home is limited to 50% of the home’s square footage. When converting a portion of the existing home or an accessory structure to an ADU, maximum size limits do not apply, so long as the existing space is not expanded beyond 150 sq.ft.

Do I have to pay impact fees on an ADU?

Impact fees are often charged by local jurisdictions to account for increased density and strain on infrastructure. An ADU of 750 sq. ft. or less is exempt from impact fees, which can present a substantial cost savings. Square footage over that amount may be subject to your local impact fees.

Does an ADU require separate utilities?

No, but you will need to size your utilities to meet the additional demand or load of the new ADU. Many older properties may need to upgrade utilities for more capacity. It may also be preferable to install separate meters for ADUs that will serve primarily as rental units.

Do I need fire sprinklers in my ADU?

Under state law, sprinklers are only required in an ADU if the primary dwelling also has sprinklers. Some local jurisdictions are using a questionable technicality to require sprinklers in ADUs added to duplexes regardless of the existence of sprinklers in the primary structure. These jurisdictions are saying that adding an ADU to a duplex changes the occupancy rating of the building, which justifies a sprinkler requirement. We believe this is in conflict with the intent of the state law. Why would you be allowed to add an ADU to a 10-unit building without adding sprinklers, but be required to add sprinklers to a duplex when adding an ADU? Nonetheless, property owners currently facing this issue have little choice but to abide by their local jurisdictions requirements.

How can I get started with an ADU?

Since the launch of new state ADU laws in 2020, we have received so many ADU-related inquiries, that we started a whole new company focused just on ADUs. Adapt Dwellings, Inc. specializes in conversion and multi-family ADUs, helping take clients from concept to approved plans. We start every project with a Feasibility Study that helps you understand your options and how easy or difficult of an undertaking an ADU will be on your property. It covers zoning, permit history, and an on-site inspection by an International Code Council Certified Combination Inspector. It also includes a financial analysis to help you make a go/no-go decision.

For projects that look feasible, the next phase is having our architect prepare a detailed set of plans and complete your local jurisdiction’s ADU application. We are not only experienced with ADU laws, but also with navigating local planning and building departments. We will work with you on a custom design you love and help walk it through the approval process.

How Long Does it Take to Get Approval for an ADU Project?

Those looking to build ADUs should allow up to 60 days for a project proposal to be approved by your local jurisdiction. If the proposal is not acted upon within 60 days the application will automatically be approved.

Ready to take the next step?

We offer a free 15-minute consultation to discuss the possibility of adding an ADU to your property. We’ll help you understand why adding an ADU can be a great move, not only for you, but for your community as well. Contact us today to see how we can help!

Make Your ADU a Reality:

Back To Top