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The Ultimate Guide to Attached ADUs in California

Accessory Dwelling Units (ADUs) have become popular in many states as a means to provide affordable housing and generate rental income.

In California, ADUs are an attractive option for homeowners and tenants alike. An attached ADU is one of the types of ADUs that’s attached to the main house. This type of ADU is a cost-efficient alternative to a detached ADU.

We’ll guide you through everything you need to know about attached ADUs in California. We’ll give you the lowdown on the rules and regulations, the cost of building one, and why it’s a smart investment.

Tips in Building your Attached ADU in California

What is an attached ADU?

An attached ADU is a second housing unit that is physically attached to the main house. It shares the same roofline, but it has a separate entrance and may have its utility system. Attached ADUs can come in different sizes, from a studio unit to a two-bedroom unit.

Rules and regulations

The California government has made it easier for homeowners to build ADUs by reducing restrictions. However, there are still rules that you should know before starting the construction. One of the most important rules is the size of the attached ADU. The maximum size of the attached ADU cannot exceed 50% of the living area of the main house, with a maximum size of 1,200 square feet. Additionally, there are setbacks and height restrictions that you should comply with. Setbacks regulate the distance between the ADU and the property line. Height restrictions limit the height of the ADU, which varies by city.

The cost of building an attached ADU

The cost of building an attached ADU in California will depend on a variety of factors, such as size, location, and finishes. The cost can range from $50,000 to $300,000. However, with the right planning and design, building an attached ADU can be a smart investment. An attached ADU can provide rental income, which can offset your mortgage or other expenses. Plus, the addition of an attached ADU can increase your home's resale value.

How to get started

If you’re thinking of building an attached ADU in California, the first step is to check the local zoning laws and building codes. You can contact your local city’s planning division to get information on the rules and regulations. Once you understand the requirements, next is to get a design that meets your needs and budget. You can hire an architect or work with a design-build firm. For convenience, connect with us at ADU Builders Group so we can help you all the way from planning to construction.


Building an attached ADU in California is a smart investment that can provide a source of rental income, create additional living space, and increase your home’s value. With the recent changes in ADU regulations, it's now easier than ever to add an attached ADU to your property. Just remember to check the local zoning laws and building codes before starting the construction.

New ADU Laws in California 2023: Changes You Must Know

2023 has been a more exciting year for California homeowners, property owners, and real estate investors. Thanks to the new California ADU laws, there are now more opportunities to build Accessory Dwelling Units (ADUs) on their properties. With these new laws, building an ADU has been more streamlined. Getting approval to build an ADU can involve many steps. Permits, setbacks, height limitations, parking standards, and other improvements must all be taken into consideration.

These are the bills-turned-laws made the process easier for homeowners. With these changes, they can confidently pursue their goal of building an ADU.


(1) Detached ADU with detached garage
It now allows the inclusion of a detached garage for an accessory dwelling unit that is detached from the proposed or existing primary dwelling.

(2) Streamlined Approval Process
A permitting agency must decide on applications related to accessory dwelling units or junior accessory dwelling units within 60 days. If the permitting agency turns down an application, it must give a complete set of comments highlighting the defects or inadequacies along with a description of how applicants can rectify it.
(3) Fewer Restrictions
Local agencies cannot impose restrictions on lot coverage, floor area ratio, open space, and front setbacks that would prevent an accessory dwelling unit of at least 800 sq ft from being built.


(1) Acceptance of Application regardless of Non-conformity to Existing Codes
An accessory dwelling unit permit application cannot be denied by local agencies due to correcting nonconforming zoning codes, building code violations or unpermitted structures that do not pose a risk to public health and safety, and unaffected by the accessory dwelling unit construction.

(2) Issuance of a Demolition Permit
If an applicant submits a permit for constructing an accessory dwelling unit, local agencies must simultaneously review and issue a demolition permit for the detached garage to be replaced. It additionally ensures that no written notice or placard is required for such demolition.

(3) Increased Maximum Height Limitation
Higher maximum ADU height limits on accessory dwelling units under certain conditions are now allowed. Units within 12 mile walking distance from a major transit stop, high-quality transit corridor, or detached on a lot with existing multi-family multi-story dwellings can be 18 feet high. If attached to a primary dwelling, the height limit can be 25 feet.

(4) No Fire Sprinklers Required
Constructing an accessory dwelling unit wouldn't be considered a Group R occupancy change under the local building code, with some exceptions. Thus, fire sprinklers needn't be installed in the existing primary dwelling merely because an accessory dwelling unit is being built.

(5) Application Acceptance regardless of Height Requirement or Setback
Local agencies are prohibited from denying an accessory dwelling unit application due to height requirements or setbacks less than 4 feet for an existing multifamily residence.

(6) No Imposed Parking Standards
Local agencies are prohibited from imposing any parking standards on an accessory dwelling unit that is included in an application to create a new single-family dwelling unit or a new multifamily dwelling on the same lot, provided that the accessory dwelling unit meets other specified requirements.

(7) Separate Entrance for JADUs
A junior accessory dwelling unit lacking a separate bathroom should have a separate entrance from the main entrance of the structure and an interior entry to the main living area.

(8) Funding Support
Grant programs for accessory dwelling units provide funding for predevelopment expenses and ensure accountability and oversight, as specified.


(1) No public hearing required for additional bedrooms
No public hearing is required for the purpose of reconfiguring space and adding bedrooms to an existing dwelling unit. This applies solely to permit applications with no more than two additional bedrooms within an existing dwelling unit.


(1) Financial Assistance
CalHFA is required to assemble a working group that would devise ways to bolster homeowners' eligibility for loans to construct ADUs and JADUs. The group, which must include certain representatives, shall also evaluate various opportunities to minimize lender risks, like loan guarantees, mortgage insurance, rental income guidelines, and managed escrow. The working group is expected to finish developing recommendations by July 01, 2023 giving homeowners something to look forward to.


With these new laws in action, building your own ADU has become easier with the government supporting its rise and with grants that are available. Surely, there'll be more improvements to further streamline the process and help more homeowners build their own ADU.

Perks of Living in an Attached ADU

Attached ADU is a great way to expand your living space, provide extra space for guests or loved ones, and even earn some extra revenue. Let's discuss the benefits of an attached ADU and why you should consider this modern housing option.

Boosts Your Property’s Value

Whether you're looking to occupy your ADU or rent it out for extra cash, a properly installed and designed ADU will significantly increase your property's value. You can make use of the extra space to take on tenants, provide a comfortable space for guests, or even turn it into a home office. Additionally, an ADU offers a permanent solution for loved ones who need to move in with you due to life circumstances.

Increased Flexibility

One of the perks of living in an ADU is the flexibility it offers. You can have a separate living area but still be close to your primary residence. This is particularly useful for family members who need care, such as aging parents or disabled relatives. With an ADU, you can maintain your privacy while also being available to help those in need.

Extra Income

Another significant benefit of an attached ADU is the extra income that you can generate from renting it out. An ADU provides a source of income that can help offset your monthly housing expenses. This can come in handy, especially if you have a mortgage to pay off. With your extra income, you can live more comfortably and even save up for future living expenses.

Creates Affordable Housing

ADUs can be the solution to the affordable housing crisis. With an ADU, it becomes easier for people who were unable to buy a primary home to build wealth. Additionally, financially-strapped homeowners facing foreclosure can use their primary home as collateral to finance a new ADU. Ultimately, the rental income they receive can be used to pay off the mortgage on a primary dwelling.

A Sustainable Housing Option

ADUs are a sustainable housing option that can help combat climate change. They are also versatile and can be used to house students, singles, and even multi-generational families. Moreover, they can be built with sustainability in mind, making use of eco-friendly materials and energy-efficient designs that can reduce your carbon footprint.


An attached ADU offers many benefits for homeowners and tenants alike. It's a flexible housing option that can provide extra living space or create a source of rental income. With an ADU, you can create living spaces that accommodate multi-generational families or provide temporary housing solutions. If you're considering an ADU, make sure to research local zoning code and regulations, get professional help, and choose your design and materials with sustainability and functionality in mind. Enjoy the perks of your new ADU!

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