Accessory Dwelling Unit Updates
How California Continues to Expand ADU Opportunities for Homeowners, Builders, and Investors
Few areas of California housing law have changed as dramatically as Accessory Dwelling Units.
Once commonly called granny flats, in-law units, or second units, Accessory Dwelling Units (ADUs) have become one of California’s primary strategies for creating housing within existing neighborhoods.
Over the last several years, the Legislature has repeatedly expanded where ADUs can be built, limited the restrictions local governments can impose, shortened approval timelines, reduced parking requirements, and created additional opportunities on both single-family and multifamily properties.
And the laws continue to evolve.
For homeowners and real estate investors, that means a property that couldn’t accommodate another legal dwelling several years ago may have very different development potential today.
What Is an ADU?
An Accessory Dwelling Unit is an independent residential dwelling located on the same property as another residential use.
ADUs can take several forms, including:
· Detached backyard homes.
· Attached additions.
· Garage conversions.
· Converted portions of existing structures.
· Units created within multifamily buildings.
An ADU generally contains its own:
· Living space.
· Sleeping area.
· Kitchen.
· Bathroom.
Unlike a traditional room addition, an ADU functions as an independent dwelling.
What Is a JADU?
A Junior Accessory Dwelling Unit (JADU) is different.
A JADU is limited to 500 square feet and is created within the space of a proposed or existing single-family residence or qualifying attached garage.
It must include an efficiency kitchen but may, under qualifying circumstances, share sanitation facilities with the primary residence.
California changed the JADU rules again effective January 1, 2026.
Under AB 1154, owner occupancy is required when the JADU shares sanitation facilities with the primary residence. If the JADU has its own sanitation facilities, that owner-occupancy requirement does not apply.
The law also now expressly prohibits JADUs from being used as short-term rentals. If rented, they must be rented for periods longer than 30 days.
ADUs Are Generally Ministerial
One of the most important features of California’s ADU laws is that qualifying applications are generally reviewed ministerially.
That means an ADU typically doesn’t require:
· A discretionary Planning Commission approval.
· A neighborhood vote.
· A subjective determination about whether the project is desirable.
Instead, the agency reviews the application against applicable objective requirements.
If the project complies, it generally must be approved.
This is one reason ADUs have become one of the most accessible forms of residential development in California.
Local Governments Have Limited Authority
Cities and counties may adopt local ADU ordinances, but those ordinances must comply with state law.
Among other limitations, local governments generally cannot:
· Impose a minimum lot size.
· Require rear or side setbacks greater than four feet for qualifying new-construction ADUs.
· Limit the number of bedrooms.
· Require replacement parking when a garage, carport, or other parking structure is converted or demolished for an ADU.
· Establish maximum ADU sizes that prevent at least an 850-square-foot ADU or a 1,000-square-foot ADU with more than one bedroom.
· Impose parking requirements in circumstances where state law prohibits them.
This is important because looking only at a city’s zoning ordinance may not tell you what state ADU law actually allows.
Parking Requirements Have Been Reduced
As discussed earlier in this series, California has substantially limited ADU parking requirements.
Local governments generally cannot require ADU parking in several situations, including certain properties:
· Located within one-half mile walking distance of public transit.
· Located within an architecturally and historically significant historic district.
· Where the ADU is created within existing or proposed primary residence or accessory structure space.
· Located near car-share.
· Where on-street parking permits are required but aren’t offered to the ADU occupant.
And when an ADU replaces or converts a garage, carport, or covered parking structure, replacement parking generally cannot be required.
For homeowners working with limited lot area, this can make the difference between an ADU being possible and impossible.
Multifamily Properties Have New Opportunities
ADU development isn’t limited to single-family homes.
This is particularly important for real estate investors.
California law allows ADUs to be created on properties containing multifamily dwellings, including conversions of qualifying non-livable areas within existing structures.
Potential conversion areas can include spaces such as:
· Storage rooms.
· Boiler rooms.
· Passageways.
· Attics.
· Basements.
· Garages.
California also expanded detached ADU opportunities on multifamily properties through SB 1211, which took effect January 1, 2025.
Under qualifying circumstances, an existing multifamily property may now be permitted to add up to eight detached ADUs, provided the number of detached ADUs does not exceed the number of existing units on the property.
That can substantially change the development potential of an existing apartment property.
Unpermitted ADUs May Have a Path to Legalization
Another significant change came through AB 2533, effective January 1, 2025.
The law expanded protections for certain unpermitted ADUs and JADUs constructed before January 1, 2020.
Local agencies generally cannot deny permits for these older units solely because they don’t comply with current building standards unless the agency determines corrections are necessary because conditions exist that would otherwise make the building substandard.
This is particularly important in California, where many properties contain older converted garages, backyard units, or informal second residences that were constructed without permits.
An existing unpermitted unit should not automatically be assumed impossible to legalize.
Coastal ADUs
ADUs within California’s Coastal Zone present additional complexity because the Coastal Act may also apply.
However, recent legislation has added processing requirements intended to prevent Coastal Development Permit review from becoming an indefinite barrier.
Current state law requires qualifying completed Coastal Development Permit applications for ADUs to be approved or denied within specified timelines, including a 60-day review period in applicable circumstances.
The California Coastal Commission also issued updated guidance in 2026 regarding implementation of these requirements.
This doesn’t mean Coastal Zone ADUs are automatically approved.
It means the Coastal Act and California’s ADU laws must be implemented together.
Local ADU Ordinances Must Follow State Law
California has also strengthened HCD’s ability to ensure local ADU ordinances comply with state requirements.
Cities and counties aren’t required to adopt their own ADU ordinance.
But if they do, they must submit it to the California Department of Housing and Community Development for review.
Current law requires an adopted ordinance to be submitted to HCD within 60 days.
If HCD identifies problems, the jurisdiction must respond.
Changes effective in 2026 further strengthen the consequences when jurisdictions fail to submit their ordinances or respond to HCD’s findings within the required timelines.
In certain circumstances, the local ordinance can become null and void, leaving the jurisdiction required to process ADUs directly under state law.
For property owners, this matters because a local ordinance isn’t necessarily the final word if it conflicts with California law.
Why Investors Should Care
ADUs are one of the most practical examples of how understanding California housing law can uncover hidden value.
Imagine two nearly identical single-family rental properties.
Most buyers evaluate:
· Purchase price.
· Existing rent.
· Taxes.
· Repairs.
· Financing.
But an investor familiar with ADU law asks another question:
“How many legal dwelling units could this property support?”
A property with an oversized backyard, detached garage, unused accessory structure, or suitable development area may have significantly more income potential than the existing rent suggests.
On multifamily properties, the opportunity can be even greater.
ADUs Can Create Multiple Investment Strategies
Depending on the property and applicable law, an ADU may create opportunities to:
· Generate additional long-term rental income.
· House family members.
· Create multigenerational housing.
· Increase property utility.
· Add housing without purchasing additional land.
· Increase overall development potential.
For investors, one of the biggest advantages is simple:
You already own the land.
Land acquisition is one of the largest costs in development.
ADUs allow additional housing to be created on land that is already part of the investment.
But ADUs Aren’t Automatically Easy
California has made ADUs easier to approve.
That doesn’t mean every ADU is easy to build.
Projects may still require evaluation of:
· Sewer or septic capacity.
· Water supply.
· Electrical service.
· Fire access.
· Structural conditions.
· Building Code compliance.
· Utility connections.
· Easements.
· Site drainage.
· Environmental constraints.
The entitlement may be streamlined while the physical realities of construction remain complicated.
This distinction is especially important when evaluating an investment property.
Rural California
ADUs can be extremely valuable in rural California, where traditional housing development may be difficult or expensive.
However, rural properties often present issues urban projects don’t.
One of the biggest is wastewater.
A property may have plenty of physical space for an ADU but insufficient septic capacity.
Other common issues include:
· Well production.
· Water storage.
· Fire access.
· Driveway standards.
· Electrical capacity.
· Steep terrain.
· Environmental resources.
For rural properties, the question isn’t simply:
“Does state law allow an ADU?”
It’s also:
“Can this particular property support one?”
Common Misconceptions
“My lot is too small for an ADU.”
Not necessarily.
California generally prohibits jurisdictions from imposing minimum lot-size requirements for ADUs.
“I converted my garage, so I have to build replacement parking.”
Generally, no.
State ADU law prohibits local agencies from requiring replacement parking when qualifying garages, carports, or other covered parking structures are demolished or converted for an ADU.
“ADUs are only allowed on single-family properties.”
False.
California law provides significant ADU opportunities on multifamily properties as well.
“An unpermitted ADU can never be legalized.”
False.
California has created significant protections for certain older unpermitted ADUs and JADUs, particularly those constructed before January 1, 2020.
“If my city’s ordinance says no, that’s the end of it.”
Not necessarily.
Local ADU ordinances must comply with California law, and HCD has authority to review and enforce those requirements.
Why This Matters
California’s ADU laws demonstrate perhaps better than any other housing legislation how quickly development rights can change.
A property owner who evaluated an ADU five or ten years ago and was told it wasn’t possible shouldn’t necessarily assume that answer is still correct.
The law has changed repeatedly.
Setbacks have changed.
Parking requirements have changed.
Approval procedures have changed.
Multifamily opportunities have changed.
Legalization rules have changed.
And California continues limiting local regulations that unnecessarily prevent ADU construction.
The Bottom Line
Accessory Dwelling Units have moved from a niche housing option to one of California’s most important housing strategies.
For homeowners, they can provide housing flexibility and additional income.
For builders, they represent a growing market.
For investors, they can unlock additional value from property already owned.
But the most important lesson is the same one we’ve seen throughout this series:
Don’t evaluate a property solely based on what’s there today.
Understand what California law allows you to create.
That additional development potential may be where the real opportunity lies.
Looking Ahead
In our next article, we’ll examine Affordable Housing Incentives and explain how California uses density, concessions, streamlined approvals, and other incentives to encourage affordable housing development.
If you’re considering an ADU or evaluating a property’s development potential, Buchanan Land Use Consulting can help determine what state law allows, identify site-specific constraints, and navigate the permitting process.
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