ADU regulations changed almost every year since 2017. That project your neighbor built five years ago? The rules aren't the same anymore. And what applies in Lafayette might be different in Orinda, even though they're right next to each other.
The good news: California law now protects you heavily. No city can ban ADUs. You don't need to live in the ADU yourself. Setbacks can't be more than 4 feet. But local rules do vary, so let me walk you through what's actually guaranteed statewide, then what each city does differently.
What California Guarantees You (The Same Everywhere)
Size Options: You can build up to 1,200 square feet for a detached ADU. Or convert existing space (like a garage or basement) with no size limit. Or add a "junior ADU" up to 500 square feet inside your home (though that one requires owner-occupancy).
Setbacks: Minimum 4 feet from your side and rear property lines. That's it. No city can require more.
Height: 16 feet standard for detached units. 18 feet if you're near major transit. 25 feet if you're attaching it to your main house.
Owner-Occupancy: You don't have to live there. You can rent it out. State law bans owner-occupancy requirements through 2030.
Parking: You probably don't need to add parking if you're near BART or another transit hub. Most of Lamorinda qualifies.
Approval Timeline: 60 days. If your plans meet the city's objective standards, they have 60 days to say yes or no. No endless back-and-forth hearings.
Impact Fees: Free pass if your ADU is under 750 square feet. Cities can't charge you.
City-by-City Breakdown (With a Friendly Heads-Up)
Lafayette
The Quick Version: Lafayette has its own local rules on top of state law. Before you spend money on plans, call the city planning department. They'll tell you exactly what size is allowed in your specific zone.
What We Know They Offer:
50% reduction in development impact fees (they temporarily cut fees in half that's real money saved)
Design standards that want your ADU to fit nicely with your house
Call Them: City of Lafayette Planning, (925) 284-1976 or https://www.lovelafayette.org/adu-permit
Orinda
The Great News: Orinda has a grant program. Actual rebate money.
Verified Incentives:
$7,500 rebate for new ADUs
$15,000 if you deed-restrict it for low-income tenants
You have 18 months from when you get your building permit to get your certificate of occupancy
Parking: One space required, unless you're within half a mile of BART (which many Orinda homes are) or you're converting an existing garage.
Call Them: City of Orinda, https://www.cityoforinda.gov/369/Accessory-Dwelling-Units
Moraga
What State Law Lets You Do: Moraga follows state standards pretty closely, which means you get flexibility. Up to 1,200 square feet is on the table.
The Smart Move: Call Moraga Planning Department to confirm what applies to your specific property. They're helpful about clarifying what's possible.
Call Them: Town of Moraga Planning Department
Danville
What You Can Build: Danville operates under Contra Costa County standards, which are pretty permissive. Up to 1,200 square feet is allowed. No minimum lot size requirement.
The Smart Move: Like Moraga, call Danville Planning Department to verify your specific property's rules. City-specific ordinances sometimes add details that matter.
Call Them: City of Danville Planning Department
Before You Spend Money on Plans
Here's the process that actually works:
Step 1: Call your city's planning department (not the building department).
Step 2: Ask these three things:
"What's the maximum ADU size I can build on my property in my zone?"
"What are my setback requirements?"
"Can I process this as ministerial approval (the 60-day timeline)?"
Step 3: Ask them to email you the answer.
Their answer determines whether your project is actually feasible. It takes 10 minutes and saves you thousands in bad planning.
The Real Talk
State law protects you. But your city adds its own rules on top. That's why "my neighbor built one and here's what they did" doesn't actually apply to your lot. Your neighbor might be in a different zone, a different city, or following rules from before 2023.
Don't guess. Call your city. Get it in writing.
Want to talk through whether an ADU makes financial sense for your specific property? What it actually costs to build? How rental income works? How it affects when you sell? Let's have that conversation. I'll help you understand what's actually possible on your lot before you spend money on anything.
-Kelly
