Can You Build an ADU Before the Main House in California?

In California's highly competitive real estate market, accessory dwelling units (ADUs) are a practical and cost-effective way to address the lack of affordable housing options. But can you build an ADU before the main house?

An ADU project is often more economical than the new construction of a traditional primary dwelling. For example, a new home created by experienced ADU builders like Abodu starts at a modest price of $228,800 for a custom independent living space.

With this in mind, some prospective homeowners may consider building an accessory structure instead of a conventional single-family home or multi-family property. However, the varying ADU laws and building codes across different municipalities in California can present certain hurdles.

What is the ideal plot of land for an ADU?

For a detached ADU, the ideal plot of land depends on many factors, such as local zoning ordinances, available space, and accessibility.

It’s best to confirm regional ADU laws with your city’s building and planning department. Alternatively, consult professionals with expertise in California ADU construction in your local area.

Features your lot should have before building an ADU

Generally, your lot should be in a residential zone and have enough open space to comply with your local government’s setback requirements. This means your accessory structure won't be too close to property lines and neighboring properties.

Likewise, check for any easements or legal restrictions limiting where you can build on your property. Easements grant specific rights to others, including neighboring properties or utility companies, to access or use a portion of your land.

Also, consider the shape of your lot and the slope of the property—ideally, the land should be flat. This will save time and money since extensive site preparation work, such as grading, will not be necessary.

Another crucial feature for your lot is access to utility connections like electricity, gas, water, and sewage. The state of California requires an ADU to be a self-contained living area with essential facilities like a bathroom and a full kitchen.

Can you build an ADU before the main house in California?

At its core, an ADU is a primary home’s accessory structure. In that sense, an accessory dwelling unit—also called a granny flat or guest house—inherently can’t exist without a primary residence.

Fortunately, local ordinances and California state laws on building ADUs are constantly evolving, so the answer to this question could change.

It’s also worth noting that certain cases exist where a California ADU can be a primary residence, and homeowners can sell their secondary unit as a condo. However, the primary dwelling would have had to exist before the ADU was built.

How do I know if there are special rules for ADUs in my region?

Head to your local government’s building and planning office to learn about special mandates concerning new ADUs in your residential zone. Feel free to ask questions like, “What are the floor area size and room limits?” and “Can you build an ADU before the main house?”

Plus, many cities and counties in California publish online resources (e.g., guides, checklists, etc.) about ADUs, such as how to acquire ADU building permits, owner occupancy guidelines, and other relevant information.

FAQs for ADUs in California

From separate backyard in-law suites for family members to garage conversions, there are many different types of ADUs—and plenty of questions that come along with them.

How much does an ADU add to property value?

A California ADU can potentially boost your real estate’s value by around 30%, so a $600,000 single-family home could eventually be worth $780,000 with a new ADU.

Keep in mind the actual increase will depend on several factors, such as the build quality and size of the main home and accessory structure. Location is another substantial factor: Real estate in Los Angeles, for example, is more likely to appreciate compared to properties in rural areas.

How much does it cost to build an ADU in California?

Throughout the state of California, the median cost for the construction of ADUs is approximately $250 per square foot.

But the true cost can fluctuate widely based on multiple factors, ranging from the accessory structure’s square footage to where it’s located, which influences building permit fees, impact fees, and labor costs.

Not to mention, the type of ADU also affects the final price tag—attached ADUs tend to be more budget-friendly than detached ADUs. For instance, since the maximum size for junior accessory dwelling units (JADUs) is 500 sq.ft., $125,000 would be the median cost to build a full-size JADU.

With Abodu, property owners can expect high-efficiency floor plans and upfront pricing for an expertly crafted prefab ADU starting at $228,800 for a turnkey studio.

How close to the property line can you build an ADU?

The permitted distance of an ADU from the property line varies by city. In general, the minimum setback ordinances are typically 4 feet or more. Check with the development office of your local municipality to confirm your zone’s regulations for building ADUs.

Can you put an ADU in your front yard in California?

It depends on your local government’s ADU laws (e.g., setback guidelines, minimum lot size, etc.) and if your primary dwelling is part of a homeowners association (HOA). Though HOAs legally cannot ban homeowners from adding an ADU to their property, they can still enforce design and placement restrictions.

Start building your dream ADU in California with Abodu

Reimagine your backyard with a timeless Abodu prefab ADU. From the initial design of your custom-built home to its crane delivery and installation, our dedicated team is ready to handle every stage of the ADU construction process.

At the end of the day, every ADU tells a unique story, and we're eager to help you tell yours.

Book a call or showroom tour today.