| Table of Contents |
| 1. What is an ADU? |
2. Benefits of Building a Permitted ADU in California |
| 3. California State ADU Laws: A Quick Overview |
| 4. Local ADU Regulations: What Cities Can (and Can't) Do |
4.1 Key Statewide ADU Regulations |
| 5. Local ADU Regulations: What Cities Can (and Can't) Do |
5.1 What Local Governments Can Regulate |
| 6. State Law Overrides: When State Rules Win |
| 7. How to Navigate State vs. Local ADU Rules |
| 8. FAQ |
What is an ADU?
An Accessory Dwelling Unit (ADU) is a fully self-contained residential unit located on the same lot as a primary home. Also called secondary suites, granny flats, backyard cottages, or in-law suites, ADUs can be detached, attached, or converted from existing structures like garages or basements. With California’s growing housing demand, ADUs have become a key solution for increasing residential density without altering neighborhood character.
Benefits of Building a Permitted ADU in California
California State ADU Laws: A Quick Overview
The California State Legislature has passed multiple laws to standardize and simplify ADU development across the state. Key ADU-related bills include AB 68, AB 881, SB 9, and AB 2221, all designed to override local restrictions that prevent homeowners from building ADUs.
Key Statewide ADU Regulations:
⏱️ 60-Day Approval Deadline: Local agencies must approve or deny ADU applications within 60 days.
🚗 No Parking Requirements: In many cases, cities cannot require parking if the ADU is near transit.
🧱 Setback Reductions: Minimum side and rear setbacks of 4 feet for detached ADUs.
🏠 By-Right Development: At least one ADU and one Junior ADU (JADU) must be allowed per lot with a single-family home.
🧾 No Owner-Occupancy Requirement: Homeowners are not required to live in the main home or ADU.
🛑 Impact Fee Exemptions: Smaller ADUs (under 750 sq ft) are exempt from most development impact fees.
Local ADU Regulations: What Cities Can (and Can't) Do
While state law takes precedence, local jurisdictions still retain some control over how ADUs are built — especially in terms of design, size, and placement.
What Local Governments Can Regulate:
ADU Height Limits: Though state law mandates a 16–18 ft minimum in most areas, cities may allow more height with special conditions.
Design Standards: Cities can impose objective design requirements like roof slope, window placement, and exterior materials.
Lot Coverage and FAR: Local rules can still dictate how much of a property can be built on, within state limits.
Historic and Coastal Zones: ADU rules may be more restrictive in historic districts or coastal zones, but must still comply with state mandates.
Permit Fees and Procedures: Each city has its own submission process, application forms, and review fees.
State Law Overrides: When State Rules Win
If a local ordinance conflicts with state law, state law prevails. For example:
A city cannot prohibit detached ADUs based on lot size alone.
A city must allow ADUs on multifamily properties with certain conditions.
A city cannot impose discretionary review if an ADU meets objective standards.
This legal framework ensures that ADUs are treated as a right—not a privilege—for most homeowners.
How to Navigate State vs. Local ADU Rules
✅ Step 1: Start with State Law
Familiarize yourself with the California Department of Housing and Community Development (HCD) guidelines to know your baseline rights.
✅ Step 2: Check Your Local Ordinance
Visit your city or county planning department’s website to download their local ADU ordinance and development standards.
✅ Step 3: Work With an ADU Expert
Professional ADU designers and consultants are well-versed in both state mandates and local nuances. They can help you avoid costly mistakes or denials.
