ADU & JADU
August 11, 2026
ADU & JADU in California: Definitions, Types, State Law, Local Rules & What Homeowners Should Know
Last reviewed: August 2026
If you are thinking about adding an Accessory Dwelling Unit (ADU) or Junior Accessory Dwelling Unit (JADU) to your California property, you have probably encountered a confusing mix of terms, rules, size limits, setbacks, parking requirements, and city regulations.
You may also have heard statements such as:
- “California allows an ADU on every property.”
- “You can build an 800-square-foot ADU anywhere.”
- “ADUs don’t need parking.”
- “A JADU is just a small ADU.”
- “The city can’t deny an ADU.”
- “You don’t need a separate utility connection.”
- “Every city has the same ADU rules.”
Some of these statements may be true in certain circumstances, but they are not universal rules.
California has established a statewide legal framework for ADUs and JADUs, but the exact requirements for a particular project depend on the property, the proposed unit, the applicable state-law pathway, and the local jurisdiction.
This guide explains the basics in plain language so homeowners can understand the difference between ADUs and JADUs, the major types of ADUs, how California state law works, how local rules fit into the picture, and why the exact property still needs to be evaluated before designing an ADU.
Important: ADU laws and local regulations can change. This article is intended for general educational purposes and is not legal or permit advice. Before designing or constructing an ADU or JADU, verify the current requirements with the city, county, building department, planning department, and other agencies having jurisdiction over your property.
What Is an ADU?
An Accessory Dwelling Unit, commonly called an ADU, is an independent residential dwelling located on the same lot as a proposed or existing primary residence.
Under California law, an ADU provides complete independent living facilities for one or more people, including permanent provisions for:
- Living
- Sleeping
- Eating
- Cooking
- Sanitation
An ADU can be attached to the main house, detached from it, or created by converting existing space, depending on the project and applicable requirements.
California’s current ADU framework is contained primarily in Government Code Sections 66310–66342. The California Department of Housing and Community Development (HCD) updated its ADU Handbook in March 2026 to reflect changes in state law that took effect January 1, 2026.
The important concept is that an ADU is intended to function as an independent dwelling unit, rather than simply being another room or addition to the primary house.
For example:
A new bedroom connected to your house is generally an addition—not an ADU.
But:
A separate unit with its own living, sleeping, cooking, and sanitation facilities may qualify as an ADU.
What Is a JADU?
A Junior Accessory Dwelling Unit, or JADU, is different from a standard ADU.
Under current California law, a JADU is a unit that:
- Contains no more than 500 square feet of interior livable space
- Is contained entirely within a proposed or existing single-family residence
- Has an efficiency kitchen
- Has a separate entrance from the main entrance of the primary residence
- May have separate sanitation facilities or share sanitation facilities with the primary residence
An efficiency kitchen is intended to provide cooking facilities appropriate to the size of the unit, including cooking appliances and food-preparation and storage areas.
A JADU is therefore not simply a very small ADU. It is a separate legal category with its own requirements under California law.
ADU vs. JADU: What Is the Difference?
The easiest way to understand the difference is to think of an ADU as a complete independent dwelling, while a JADU is a smaller unit created within the walls of a single-family residence.
| Feature | ADU | JADU |
|---|---|---|
| Maximum statutory size | Depends on applicable pathway | 500 sq. ft. interior livable space |
| Independent dwelling | Yes | More limited |
| Location | Attached, detached, or qualifying conversion | Within a single-family residence |
| Kitchen | Full independent kitchen | Efficiency kitchen |
| Bathroom | Independent sanitation facilities | May be separate or shared |
| Separate entrance | Depends on configuration | Required |
| Detached unit possible? | Yes | No |
| Parking | Depends on state/local rules and pathway | Additional parking cannot be required |
| Owner occupancy | Generally not required for ADUs | May apply when sanitation facilities are shared |
| Separate sale | Possible only under specific legal pathways | Generally no separate sale |
The exact requirements should always be checked against the current law and local regulations.
What Are the Different Types of ADUs?
There is no single physical design for an ADU.
An ADU can take several forms depending on the property and the existing building.
The most common configurations include:
- Attached ADU
- Detached ADU
- Garage conversion ADU
- Interior conversion ADU
- New construction ADU
- JADU
Let’s look at each one.
1. Attached ADU
An attached ADU is physically connected to the primary residence.
For example, it could be:
- A rear addition
- A side addition
- A second-story addition
- An addition connected to the existing house
- A unit occupying part of an attached structure
An attached ADU can be a good option when the property has limited backyard space or when a detached structure is not practical.
However, the fact that an ADU is attached does not mean it is treated exactly like a normal room addition.
The project still needs to satisfy applicable ADU, building, zoning, and other requirements.
2. Detached ADU
A detached ADU is physically separate from the primary residence.
This is the classic backyard ADU that many homeowners picture when they hear the term “ADU.”
Examples include:
- Backyard cottages
- New detached living units
- Detached studio units
- Detached two-story ADUs where permitted
- New structures replacing qualifying existing accessory structures
Detached ADUs can provide greater privacy between the main residence and the accessory unit.
However, they also require careful evaluation of:
- Setbacks
- Height
- Lot configuration
- Access
- Utilities
- Fire safety
- Drainage
- Existing structures
- Property coverage
- Local standards
3. Garage Conversion ADU
A garage conversion transforms an existing garage into an ADU.
This can be an attractive option because the basic structure already exists.
However, homeowners should not assume that converting a garage is simply a matter of adding drywall, a bathroom, and a kitchen.
The existing garage may need to be evaluated for:
- Foundation
- Floor elevation
- Ceiling height
- Insulation
- Exterior walls
- Windows
- Doors
- Natural light
- Ventilation
- Fire separation
- Electrical service
- Plumbing
- HVAC
- Energy compliance
- Structural conditions
- Existing permits
An existing garage may also have been constructed under older requirements or may contain unpermitted modifications.
A site and building evaluation should therefore be performed before assuming a garage can easily become an ADU.
4. Interior Conversion ADU
An ADU can sometimes be created by converting existing space within a residence or qualifying accessory structure.
Examples might include:
- An unused portion of a house
- Existing enclosed space
- A qualifying garage
- Another qualifying accessory structure
This can be advantageous because much of the building envelope already exists.
However, existing space still needs to be evaluated for applicable building and safety requirements.
The fact that a space already exists does not automatically make it legal residential space.
5. New Construction ADU
A new construction ADU is a new building constructed specifically as an accessory dwelling unit.
This is often the most flexible option from a design perspective because the unit can be planned around the intended layout from the beginning.
A new detached ADU may include:
- Living area
- Bedroom
- Kitchen
- Bathroom
- Laundry
- Storage
- Outdoor space
- Covered patio
- Parking, where applicable
However, new construction also means the entire building must be designed and permitted as new construction.
That can involve:
- Site planning
- Foundation design
- Structural plans
- Energy compliance
- Electrical
- Plumbing
- Mechanical systems
- Exterior elevations
- Building sections
- Construction details
- Utility coordination
6. JADU
A JADU is its own category and should not simply be considered a “tiny ADU.”
A JADU must be contained entirely within a single-family residence.
Under current state law, an attached garage is treated as part of the single-family residence for purposes of creating a JADU.
A JADU requires:
- Maximum 500 square feet of interior livable space
- A separate entrance
- An efficiency kitchen
- Appropriate living/sleeping space
- Sanitation facilities that may be separate or shared
If the JADU shares sanitation facilities with the primary residence, owner-occupancy rules may apply under the JADU statute.
A JADU also cannot simply be sold as a separate property from the primary residence.
How Does California State ADU Law Work?
California has established a statewide legal framework governing ADUs and JADUs.
The primary statutory framework is found in California Government Code Chapter 13, Sections 66310–66342.
The California Department of Housing and Community Development maintains current ADU resources and updated its ADU Handbook in March 2026 to reflect changes in state law.
The state framework establishes rules concerning matters such as:
- Where ADUs can be created
- ADU size
- Height
- Setbacks
- Parking
- Fees
- Utilities
- Fire sprinklers
- Owner occupancy
- Rental restrictions
- Review procedures
- JADUs
- Existing unpermitted ADUs
The important thing to understand is that state law establishes a framework—it does not mean every ADU is identical.
Different statutory pathways can provide different protections and development standards.
What Does “Ministerial Approval” Mean?
You may see the word “ministerial” frequently when researching ADUs.
In simple terms, ministerial approval means the application is reviewed against objective requirements rather than being subject to discretionary approval based on subjective design judgment.
For qualifying ADU applications, the local agency generally must process the application through the ministerial process established by state law.
This does not mean:
“The city has to approve anything you draw.”
The proposed project still needs to comply with the requirements applicable to that particular ADU pathway.
The important distinction is that a qualifying ADU is generally not supposed to be subjected to the same discretionary land-use approval process used for many other development projects.
What Is a “State-Exempt” or Section 66323 ADU?
You may hear homeowners, designers, or contractors refer to a “state-exempt ADU,” “state-mandated ADU,” or “66323 ADU.”
HCD uses the term “66323 Units” for ADUs and JADUs created under Government Code Section 66323. These units are sometimes also called “state mandated” or “state exempt” ADUs.
Section 66323 identifies specific categories of ADUs and JADUs that must receive ministerial approval and are subject to the standards specifically authorized by that section.
Depending on the category, these can include:
- ADUs created within existing or proposed single-family dwelling space
- ADUs created within qualifying existing accessory structures
- JADUs
- New detached ADUs on lots with existing or proposed single-family dwellings
- Certain ADUs within existing non-livable areas of multifamily structures
- Certain detached ADUs associated with multifamily properties
One important feature of §66323 is that local agencies generally may not impose development or design standards on qualifying 66323 units that are not authorized by that section. HCD specifically identifies standards such as lot coverage, front setbacks, and design standards as examples that generally do not apply to qualifying 66323 units unless authorized by the statute. Building-code and health-and-safety requirements still apply.
Does “state-exempt” mean no permit is required?
No.
This is an important misconception.
A “state-exempt” or Section 66323 ADU is still a permitted construction project.
The term refers to the statutory pathway and the development standards that may or may not be applied—not an exemption from building permits or building-code compliance.
CADnest Design prepares plans based on the laws, codes, and jurisdictional requirements in effect at the time of drafting. The final determination of eligibility, compliance, and permit approval rests with the applicable authority having jurisdiction (AHJ).
How Many ADUs Can You Have on a Single-Family Property?
This is one of the most important changes in the 2026 California ADU framework.
Older ADU information often described a single-family property as having the option for one ADU and possibly one JADU.
That description is now incomplete.
Effective January 1, 2026, Senate Bill 543 clarified the language of Government Code Section 66323 so that qualifying units can be created “in any combination.” HCD’s 2026 Handbook confirms that the qualifying §66323 unit types can be combined.
For a qualifying lot with an existing or proposed single-family residence, the state framework can allow:
- One ADU created within existing or proposed space
- One JADU
- One new detached ADU
These are not necessarily alternatives where the homeowner must choose only one.
For example, a qualifying property could potentially have:
Primary Residence
1 converted/interior ADU
1 detached new-construction ADU
1 JADU
HCD also states that, in addition to the units described in Section 66323, a local agency must allow at least one unit described in Section 66314. The §66314 ADU can be subject to the objective development and design standards allowed under the local ADU ordinance.
That means the state framework can potentially allow a qualifying single-family property to support multiple additional dwelling units beyond the primary residence.
Does every property automatically get all of these units?
No.
This is extremely important.
The law creates minimum allowances for qualifying circumstances, but each proposed unit still needs to satisfy the requirements applicable to its particular pathway.
The actual property must be evaluated for:
- Existing structures
- Lot configuration
- Fire and life safety
- Access
- Utilities
- Building-code requirements
- Existing permits
- Applicable local standards for the §66314 unit
- Other property-specific conditions
The fact that state law allows a particular combination does not mean that the physical property can necessarily accommodate it.
CADnest Design prepares plans based on the standards in effect at the time of drafting. The AHJ makes the final determination regarding eligibility and permit approval.
How Big Can an ADU Be?
There is no single answer such as:
“An ADU can only be 800 square feet.”
That statement is incomplete.
California law establishes different size protections depending on the applicable pathway.
For ADUs subject to Government Code Section 66321, a local agency generally cannot establish a maximum ADU size below:
- 850 square feet of interior livable space, or
- 1,000 square feet of interior livable space for an ADU with more than one bedroom.
State law also establishes an allowance for an ADU of at least 800 square feet of interior livable space with four-foot side and rear setbacks under the circumstances specified by the statute.
At the same time, Section 66323 contains a specific pathway for a detached new-construction ADU on a qualifying single-family lot with a maximum of 800 square feet of interior livable space.
This is why simply saying “California ADUs are limited to 800 square feet” is misleading.
The applicable ADU pathway matters.
How Big Can a JADU Be?
A JADU is much more straightforward in this respect.
A JADU may contain no more than 500 square feet of interior livable space.
It must also be contained within a proposed or existing single-family residence, subject to the specific statutory requirements.
The 500-square-foot limit is based on interior livable space, which is an important distinction when comparing a JADU’s allowable area with other measurements that may appear on architectural plans.
ADU Height Requirements
Height requirements can vary depending on:
- Whether the ADU is attached or detached
- Whether the property contains a single-family or multifamily dwelling
- Whether the property is near qualifying transit
- The ADU’s statutory pathway
- The applicable local ordinance
California law establishes minimum height allowances that local agencies must accommodate in specified circumstances.
For example, current state law provides different height allowances for qualifying detached and attached ADUs depending on the property and location. The Section 66323 detached ADU pathway has its own maximum-size and height framework.
Because the exact height allowance depends on the statutory pathway, homeowners should not rely on a single number found in a generic ADU article.
Before designing an ADU around a particular height, verify which state-law pathway applies to the project and confirm the local jurisdiction’s current implementation.
ADU Setbacks
Setbacks are one of the most common questions homeowners ask.
A homeowner may ask:
“How far does my ADU need to be from the property line?”
The answer depends on the ADU type and applicable legal pathway.
For certain new-construction ADUs covered by Section 66323, state law provides a four-foot side and rear setback framework.
For other ADUs, different standards can apply.
Existing-space conversions can also be subject to different rules, including requirements related to fire and safety.
This means you should not assume that the setback requirement for a normal accessory structure or the primary residence automatically applies to an ADU.
At the same time, front setbacks, fire safety, access, historic resources, and other site-specific conditions can still matter.
A property should therefore be evaluated before deciding where the ADU can be placed.
CADnest Design prepares plans according to the applicable standards in effect at the time of drafting. The final determination of setback compliance rests with the AHJ.
ADU Parking Requirements
Parking is another area where outdated information causes confusion.
It is not accurate to simply say:
“ADUs don’t need parking.”
California law limits local agencies’ ability to require parking for many ADUs and prohibits parking requirements for certain categories.
State law includes exemptions related to factors such as:
- Proximity to public transit
- Historic districts
- Existing or proposed space within a primary dwelling or accessory structure
- Certain other statutory circumstances
State law also limits replacement-parking requirements in qualifying situations.
For JADUs, California law prohibits a local agency from requiring additional parking as a condition of approving a JADU.
Local regulations and property-specific conditions can still matter for other ADU pathways.
For example, Pasadena’s current ADU regulations contain specific parking requirements and exemptions based on factors such as transit proximity, existing-space conversions, historic districts, and other conditions.
This illustrates why a generic statement such as “ADUs don’t require parking” can be misleading.
The applicable ADU pathway and local jurisdiction should always be verified before assuming that no parking is required.
Fire Safety and Sprinklers
Fire safety is an important part of every residential construction project.
However, adding a qualifying ADU does not automatically mean that the entire primary residence must receive a new sprinkler system.
For qualifying Section 66323 ADUs and JADUs, California law provides that fire sprinklers are not required in the ADU or JADU if sprinklers are not required for the primary residence.
The construction of such a unit also does not automatically trigger a requirement to install sprinklers throughout an existing multifamily building.
This does not mean that an ADU is exempt from fire and life-safety requirements.
Other issues can still include:
- Fire access
- Emergency egress
- Fire-resistance construction
- Smoke alarms
- Carbon monoxide alarms
- Exterior openings
- Separation requirements
- Local fire department requirements
- High fire hazard conditions
- Water supply and fire-flow considerations where applicable
Projects in wildfire-prone areas require especially careful review.
Utilities and ADUs
An ADU can involve several utility considerations:
- Electrical
- Water
- Sewer
- Gas
- Stormwater
- Communications
Whether an ADU requires a separate utility connection depends on the type of ADU and applicable law.
For certain Section 66323 ADUs and JADUs, California law limits the ability of local agencies and certain utility providers to require new or separate utility connections and related fees. Other ADUs can be subject to different utility requirements.
This is one reason it is important to determine the specific ADU pathway before making assumptions about utility costs.
What about a separate address?
An ADU may receive an address or unit designation depending on the local jurisdiction and addressing requirements.
But an additional address does not mean that the ADU is automatically a separate legal parcel.
An ADU is generally located on the same lot as the primary residence.
Can You Rent an ADU or JADU?
Yes.
ADUs and JADUs can generally be used as rental housing, subject to applicable state and local restrictions.
One important state-law requirement is the minimum rental term.
Qualifying ADU and JADU rentals must generally be for a term longer than 30 days.
This means an ADU should not simply be treated as a short-term vacation rental under the state ADU framework.
Local short-term-rental regulations can impose additional restrictions.
If you are planning an ADU specifically as an investment property, it is important to research the local rental regulations before designing the unit.
Can You Sell an ADU Separately?
Generally, an ADU is not simply a separate property that can be sold independently from the primary residence.
However, California law does provide specific pathways that allow a local jurisdiction to permit the separate conveyance of a primary dwelling and ADU as condominiums under certain conditions.
HCD’s current handbook explains that these provisions are subject to requirements involving matters such as the Davis-Stirling Common Interest Development Act, the Subdivision Map Act, safety inspection, lienholder consent, and other conditions.
So it is more accurate to say:
An ADU generally cannot simply be sold separately, but California law provides specific pathways for separate conveyance under qualifying circumstances.
If separate sale or ownership is one of your goals, the property should be evaluated under the applicable current law before the project is designed around that assumption.
What About an Existing Unpermitted ADU?
This is a very important topic because many Southern California homes have additions or converted garages that were constructed without permits.
California law contains specific provisions for certain previously unpermitted ADUs and JADUs constructed before January 1, 2020.
Under the current framework, a local agency can inspect such a unit for compliance with health and safety standards and provide recommendations for correcting those conditions. The law also provides protections against penalizing an applicant simply for having the qualifying unpermitted ADU or JADU.
This does not mean that every unpermitted structure automatically becomes legal.
Instead, the law provides a pathway intended to help qualifying existing units obtain permits while addressing necessary health and safety issues.
If you have an existing unpermitted garage conversion or backyard unit, it is worth investigating its history before assuming that it must be demolished or completely rebuilt.
State Law vs. City and County Rules
This is probably the most important concept for homeowners to understand.
California State Law
California establishes the statewide ADU framework.
It determines many of the fundamental rules governing:
- Eligibility
- Size
- Height
- Setbacks
- Parking
- Fees
- Utilities
- JADUs
- Review procedures
- Rental restrictions
Local City or County Rules
A city or county may adopt its own ADU ordinance, but that ordinance must comply with California’s state ADU law.
HCD reviews local ADU ordinances and can take enforcement action when local requirements do not comply with state law.
This means that two homeowners in different cities can have different site-specific requirements even though both are governed by the same California state ADU framework.
For example, a property in Pasadena is subject to the City of Pasadena’s applicable regulations.
A property in unincorporated Los Angeles County is subject to Los Angeles County’s applicable regulations.
A property inside the City of Los Angeles is not governed by Los Angeles County’s unincorporated zoning regulations simply because it is located within Los Angeles County geographically.
That distinction is extremely important.
Example: Los Angeles County
For CADnest clients, Los Angeles County is particularly important.
But there is a major distinction between:
Los Angeles County
and
City of Los Angeles.
They are different jurisdictions with different planning and permitting systems.
For properties in unincorporated Los Angeles County, the County has its own ADU ordinance.
The Los Angeles County Planning Department states that the Board of Supervisors approved an amendment to the County’s ADU Ordinance in October 2024, and that the changes became effective August 28, 2025. The amendment updated local standards to comply with state ADU law.
Los Angeles County is also currently evaluating a proposed 2026 ADU Ordinance Amendment.
However, as of the County’s July 2026 update, those 2026 amendment materials remain in the draft evaluation phase. The County explicitly states that the draft materials do not have the force of law and that existing County and State regulations continue to govern current ADU projects.
This is an excellent example of why homeowners should be careful when reading online ADU information.
A draft ordinance, proposed change, or old blog post is not necessarily the rule that applies to your project today.
Example: Pasadena
Pasadena is another useful example because the city has its own ADU regulations and permitting process.
The City of Pasadena currently provides specific regulations for ADUs and JADUs and allows homeowners to apply for and submit ADU plans electronically. The city’s current regulations also distinguish between different ADU configurations, including converted, attached, detached, and JADU options.
Pasadena’s current ADU regulations became effective May 20, 2024.
The city also has specific parking rules and exemptions, fee reductions, and other local programs that can affect an ADU project.
The important lesson is:
Pasadena’s rules should not automatically be applied to a property in another city.
Before preparing plans, identify the actual jurisdiction responsible for the property.
What Plans Are Needed for an ADU?
Once you determine that your property can support an ADU, the next question is usually:
“What drawings do I need?”
An ADU permit package can include several different drawings and supporting documents.
Depending on the project, these may include:
- Site plan
- Existing floor plan
- Proposed floor plan
- Roof plan
- Exterior elevations
- Building sections
- Construction details
- Structural plans
- Structural calculations when required
- Electrical information
- Plumbing information
- Mechanical/HVAC information
- Energy compliance documentation
- Green-building documentation
- Other jurisdiction-specific forms or documents
A detached new ADU, for example, generally requires much more information than simply drawing the proposed floor plan.
The plans need to communicate:
Where the ADU is located → how large it is → how it looks → how it is constructed → how utilities are provided → how it complies with applicable requirements.
For a detailed explanation of residential permit drawings, see our article:
“What Drawings Are Needed for a Building Permit? A Homeowner’s Guide to Permit Plans.”
ADU vs. Room Addition
Another common misconception is that an ADU is simply a room addition with a kitchen.
It is not.
A room addition expands the primary residence.
An ADU creates an additional dwelling unit.
For example:
Room Addition
You add:
- Bedroom
- Bathroom
- Family room
The new rooms remain part of the primary residence.
ADU
You create an additional dwelling unit containing its own:
- Living space
- Sleeping space
- Cooking facilities
- Sanitation facilities
The two projects may look similar from the outside, but they can have very different permitting and code considerations.
This distinction should be established early in the design process.
What Should You Do Before Designing an ADU?
Before you start drawing an ADU, it is a good idea to go through a basic property evaluation.
1. Identify the correct jurisdiction
Determine whether the property is located in:
- A city
- Unincorporated county
- Another special jurisdiction
Do not assume that county rules apply simply because the property is geographically within the county.
2. Verify the property’s zoning
Confirm the applicable zoning and whether an ADU is permitted under the property’s circumstances.
3. Review existing structures
Determine:
- What currently exists
- What is permitted
- What may have been added later
- Whether there are existing garages or accessory structures
4. Determine the ADU type
Decide whether the project is likely to be:
- Attached
- Detached
- Garage conversion
- Interior conversion
- New construction
- JADU
5. Determine the applicable state-law pathway
This is important because different statutory pathways can have different rules regarding:
- Size
- Setbacks
- Height
- Utilities
- Development standards
6. Evaluate the site
Look at:
- Property lines
- Existing buildings
- Setbacks
- Easements
- Access
- Slopes
- Utilities
- Fire conditions
- Trees
- Drainage
- Other site constraints
7. Check the existing building
If the ADU involves an existing structure, verify its current condition and permit history.
8. Prepare accurate existing-condition drawings
Accurate measurements are essential for determining what can realistically fit on the property.
9. Develop the proposed plans
Once the basic feasibility has been established, the architectural plans can be developed.
10. Coordinate the permit package
Structural, energy, electrical, plumbing, mechanical, and other required documents should be coordinated with the architectural drawings.
A Simple Example
Imagine a homeowner has a single-family home on a 6,000-square-foot lot.
They want to build a detached 700-square-foot backyard ADU.
At first glance, it may seem simple:
“There is enough backyard space, so we can build it.”
But several questions need to be answered first:
- What city is the property in?
- What is the zoning?
- What are the existing setbacks?
- Is there an existing garage?
- Are there easements?
- Is the property in a special fire hazard area?
- What height is allowed?
- What ADU pathway applies?
- How will water and sewer connect?
- Is there adequate electrical capacity?
- Are there access requirements?
- Are there existing unpermitted structures?
- What energy requirements apply?
- What structural design is required?
And under the current 2026 framework, another question may also be important:
Are there additional ADU/JADU opportunities available on the property under Sections 66323 and 66314?
Only after those questions are answered can the homeowner know whether the proposed design is actually feasible.
This is why ADU design should begin with property research—not just drawing a floor plan.
Why ADU Rules Can Be Confusing
One reason ADU information online is so confusing is that several layers of regulations can apply at the same time.
You may have:
California State Law
↓
Local ADU Ordinance
↓
Zoning / Planning Requirements
↓
Building Code
↓
Fire and Life Safety Requirements
↓
Energy Requirements
↓
Utility Requirements
↓
Property-Specific Conditions
The result is that two properties that look almost identical may have different permitting considerations.
This is also why an ADU plan found online or used successfully in another city should not simply be copied for a different property.
A plan that works for one property may not work for another because of:
- Lot dimensions
- Setbacks
- Height
- Fire access
- Existing structures
- Utilities
- Easements
- Zoning
- Local standards
- The applicable statutory ADU pathway
Final Takeaway
ADUs and JADUs have become an important part of California’s housing landscape, but understanding the rules requires more than knowing the basic definition.
An ADU is an independent dwelling unit located on the same lot as a primary residence.
A JADU is a smaller unit—up to 500 square feet of interior livable space—contained within a single-family residence and subject to its own requirements.
ADUs can take several forms, including:
- Attached ADUs
- Detached ADUs
- Garage conversions
- Interior conversions
- New construction ADUs
California provides a statewide legal framework governing ADUs and JADUs, including rules concerning size, height, setbacks, parking, fees, utilities, fire safety, rentals, and permit processing.
The 2026 changes are especially important because qualifying Section 66323 ADUs and JADUs can be combined. On a qualifying single-family property, the state framework can allow:
- One ADU created within existing or proposed space
- One JADU
- One detached new-construction ADU
And HCD’s current guidance states that, in addition to the units described in Section 66323, a local agency must allow at least one ADU under Section 66314, subject to the applicable objective standards.
That means the number of additional dwelling units potentially available on a property can be greater than many homeowners realize.
But state law is only part of the picture.
The property’s city or county, existing structures, zoning, site conditions, utilities, fire conditions, and the specific ADU pathway can all affect the project.
The most important thing for a homeowner to understand is:
There is no single “California ADU design” that works for every property.
Before investing in detailed plans, determine where the property is located, what rules apply, what type of ADU you are proposing, whether multiple ADU/JADU pathways can be combined, and which state-law pathway best fits the project.
Once those questions are answered, the design and permit process becomes much more straightforward.
Planning an ADU or JADU?
If you are considering an ADU, JADU, garage conversion, detached ADU, attached ADU, or other residential project, the first step is understanding what can actually be built on your property.
CADnest Design provides residential drafting and permit-plan preparation services for homeowners and construction professionals in Southern California.
Whether you already have a design in mind or are starting with an existing garage, backyard, or portion of your home, a proper property evaluation and coordinated permit plan set can help identify potential issues before you reach the plan-check stage.
Request a project quote or contact CADnest Design to discuss your project.
Important Update Note
Last reviewed: August 2026
California ADU law continues to change. The information in this article reflects California state law and official local-government information available at the time of review.
For current projects, homeowners should verify the applicable requirements directly with the jurisdiction having authority over the property.
The California Department of Housing and Community Development maintains the state’s current ADU resources and its ADU Handbook was updated in March 2026.
For unincorporated Los Angeles County properties, the County’s current ADU ordinance amendment became effective August 28, 2025. The County’s proposed 2026 ordinance amendment remains under evaluation and, as of July 2026, does not have the force of law.
CADnest Design prepares plans based on the laws, codes, and jurisdictional requirements in effect at the time of drafting. The final determination of eligibility, compliance, required corrections, and permit approval rests with the applicable authority having jurisdiction (AHJ).