California’s housing crunch isn’t slowing down. Whether you’re looking to expand your living space, rent out a second unit, or increase property value, Accessory Dwelling Units (ADUs) are a practical solution. But if you're planning to build one, it’s critical to understand the laws that guide their construction, design, and sale.
This guide breaks down California's current ADU laws into actionable information. No filler. Just what you need to move forward.
What Is an ADU?
An Accessory Dwelling Unit (ADU) is a second residential unit located on the same lot as a primary residence. It can be attached, detached, or converted from an existing space like a garage.
Why California Keeps Changing ADU Laws
California lawmakers have been revising ADU regulations for the past few years. The goal: add more housing options without expanding city boundaries. To make that happen, state laws now override most local restrictions.
What used to be a lengthy, expensive process is now streamlined. Homeowners today have more freedom to build ADUs than ever before.
Types of ADUs Allowed in California
There are three main categories:
1. Detached ADUs
A separate unit, usually built in the backyard. Maximum size: 1,200 square feet in most cities. Some municipalities allow more under local amendments.
2. Attached ADUs
Connected to the main house, often sharing one wall. These must be smaller than 50% of the main home’s square footage, or no more than 1,200 square feet—whichever is less.
3. Junior ADUs (JADUs)
Converted spaces within the main home (like a bedroom or garage). JADUs are limited to 500 square feet and must have an efficiency kitchen. A bathroom is optional if one exists in the main structure.
Key California ADU Laws to Know (As of 2025)
You don’t need to sift through government PDFs. Here’s what matters right now:
✅ No More Owner-Occupancy Rule
Until 2025, homeowners don’t have to live in either the primary home or the ADU. This opens the door for investors or landlords.
✅ 4-Foot Setbacks
Detached ADUs only need 4-foot setbacks from the rear and side property lines.
✅ One ADU + One JADU Allowed
Every single-family home can have both a standard ADU and a JADU. Duplexes and multifamily properties can add multiple units, depending on existing space.
✅ 60-Day Permit Approvals
Cities must approve or deny ADU permits within 60 days. No more open-ended delays.
✅ No Parking Requirements (in most cases)
If you’re within half a mile of public transit, you don’t have to add parking for your ADU.
✅ No Minimum Lot Size
Even small lots qualify for ADUs. Local governments can’t enforce a minimum size requirement.
Utility Hookups and Fees
Detached ADUs usually require their own utility connections. However, impact fees (the ones that used to cost thousands) are waived for units under 750 square feet. Anything over that may still trigger fees, depending on the city.
Some cities allow shared water or sewer lines between the primary home and ADU, while others require separate connections.
Local Rules vs. State Law
Local governments can set additional guidelines, but they can’t block you from building an ADU if your plan meets state law. Common local rules include design standards, maximum height restrictions, or landscape buffering.
Still, state law is clear: local ordinances cannot make it functionally impossible to build.
If your city gives you conflicting info, cite state laws like AB 68, AB 881, and SB 897. These bills strengthen homeowner rights and limit red tape.
HOA Rules Don’t Apply
Homeowners’ Associations (HOAs) can’t ban you from building an ADU. They might try to enforce design standards, but they can’t outright deny you the right to build.
Selling an ADU Separately (AB 1033)
As of 2024, some cities now allow ADUs to be sold separately from the main house—kind of like a condo.
But it’s not statewide. Municipalities have to opt in. Check with your local planning department before pursuing this option. If allowed, both the main home and ADU must be converted into separate legal lots or condominium units. This requires a recorded subdivision map, new utility hookups, and property taxes for both units.
Fire Safety Requirements
Most ADUs don’t require fire sprinklers unless your main home does. If your home has them, your ADU probably will too.
Also, if you live in a Very High Fire Hazard Severity Zone, there may be extra rules—like defensible space or ember-resistant vents. These are city-specific, so check early.
Can You Rent Out an ADU?
Yes. Long-term rental is allowed statewide. Short-term rentals (under 30 days) depend on city rules. Some ban them outright.
If you’re planning to use your ADU for Airbnb, do your homework. Fines for illegal short-term rentals can be steep.
How Much Does It Cost to Build an ADU?
Costs vary. Here’s a general breakdown:
Garage conversion: $80,000 to $130,000
Attached ADU: $100,000 to $180,000
Detached ADU: $150,000 to $300,000+
These numbers can fluctuate based on site conditions, finishes, permits, and city fees. Always get a detailed estimate before starting.
Pro tip: Some contractors offer “all-in-one” ADU packages that streamline planning, permitting, and construction. This can save time and reduce surprises.
Financing Your ADU
You’ve got options:
- Cash-Out RefinanceTap into existing home equity.
HELOC (Home Equity Line of Credit)
Flexible, interest-only during the draw period.ADU Construction Loans
Offered by some credit unions and local banks.Renovation Mortgages
Like Fannie Mae’s HomeStyle Loan.
Incentive programs may also be available at the city or county level. For example, some local governments offer pre-approved ADU plans or waived permit fees.
What If the City Denies Your Permit?
First, get the denial in writing. Then review state law and compare it to the reason given.
If the denial contradicts California law, file an appeal. Or consult a land-use attorney who specializes in ADU regulations. Don’t assume the city is right. Mistakes happen.
ADUs Are the Future—But You Have to Follow the Rules
Adding an ADU can be a game-changer. Whether you’re boosting property value, housing family, or generating passive income, California law is now in your corner.
That said, stay compliant. Know your zoning, setbacks, utility requirements, and whether your city allows separate resale. Getting these details wrong can cost thousands—or stall your build entirely.
Final Thoughts
California ADU laws are designed to be homeowner-friendly. Still, local rules, building codes, and utility logistics can complicate things.
If you’re serious about building, start with these three steps:
Talk to a local ADU builder or contractor
Get a feasibility assessment for your lot.Request a zoning verification letter from your city
This confirms what’s allowed under local ordinances.Create a realistic budget
Include construction, fees, hookups, and a contingency buffer.
