What are the setback requirements for ADUs in California?

California requires a minimum 4-foot rear and side setback for new ADUs. However, ADUs converting existing structures (like garages) may have no setback requirements. Some cities have additional requirements, so check with your local planning department.

Do I need owner-occupancy for an ADU?

As of January 1, 2025, California law prohibits owner-occupancy requirements for ADUs until January 1, 2030. This means you can rent out both your main home and ADU without living on the property, though some cities are challenging this.

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

ADU construction costs in California typically range from $150,000 to $350,000 for a detached new-build ADU, depending on size and finishes. Garage conversions cost $100,000-$200,000. Prefab ADUs range from $100,000-$250,000 installed.

How long does the ADU permit process take?

California law requires cities to approve or deny ADU permits within 60 days of a complete application. However, getting to a 'complete' application may take additional time for plan corrections. Total timeline from design to permit is typically 2-4 months.

California ADU Laws 2025: Complete Homeowner's Guide

Q: How big can an ADU be in California?

California state law allows detached ADUs up to 1,200 square feet. Attached ADUs can be up to 50% of the primary dwelling's floor area or 1,200 square feet, whichever is less. Junior ADUs (JADUs) are limited to 500 square feet and must be within the existing home or attached garage.

California has become the national leader in ADU (Accessory Dwelling Unit) construction, with over 25,000 ADU permits issued annually. State legislation has progressively made it easier and more affordable for homeowners to add these "granny flats," "in-law suites," or "backyard cottages" to their properties.

This comprehensive guide covers everything you need to know about California ADU laws in 2025, including recent legislative changes, size and setback requirements, permit processes, and cost considerations.

What is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary housing unit on a single-family residential lot. California recognizes three types:

Detached ADU

A standalone structure separate from the main house. This is the most common type and offers the most flexibility in design and placement. California allows detached ADUs up to 1,200 square feet.

Attached ADU

An addition to the existing home with its own entrance, kitchen, and bathroom. Attached ADUs can be up to 50% of the primary dwelling's floor area or 1,200 square feet, whichever is less.

Junior ADU (JADU)

A small unit of up to 500 square feet created within the existing home or attached garage. JADUs must share a bathroom with the main home unless they include their own. A property can have both a JADU and an ADU.

2025 California ADU Size Requirements

ADU Type	Maximum Size	Notes
Detached ADU	1,200 sq ft	Can be two stories in many jurisdictions
Attached ADU	1,200 sq ft or 50% of main home	Whichever is less
Junior ADU (JADU)	500 sq ft	Must be within existing structure
Garage Conversion	No limit beyond garage footprint	Setback requirements waived

Multiple ADUs Allowed

California law now allows multiple ADUs on a single property. Single-family lots can have one ADU plus one JADU. Multi-family properties can add up to 2 detached ADUs plus convert existing non-habitable space (like storage or laundry rooms) into ADUs.

Setback and Placement Requirements

California has standardized minimum setback requirements to prevent local jurisdictions from making ADUs impractical:

Rear setback: 4 feet minimum
Side setback: 4 feet minimum
Height: 16 feet for detached ADUs, or up to 25 feet if within ½ mile of transit
Lot coverage: Cannot exceed local lot coverage limits, but ADU of 800 sq ft must always be allowed

Exceptions to Setbacks

Setback requirements do not apply when:

Converting an existing garage, carport, or accessory structure
The ADU is entirely within the existing space of the primary dwelling
An existing structure being converted already doesn't meet setback requirements

Parking Requirements

California has significantly relaxed parking requirements for ADUs. No additional parking is required when:

The ADU is within ½ mile of public transit
The ADU is within a historic district
The ADU is part of an existing primary residence or accessory structure
On-street parking permits are required but not available to the occupant
There is a car-share vehicle within one block

When parking is required, one space per ADU is sufficient, and it can be tandem or in setback areas.

The ADU Permit Process

Step 1: Pre-Application Research

Before starting the permit process:

Check your lot size and zoning designation
Review any HOA CC&Rs (though HOAs cannot prohibit ADUs, they can set reasonable standards)
Determine utility connection requirements
Assess site conditions and access

Step 2: Design and Plans

You'll need construction drawings that include:

Site plan showing ADU placement
Floor plans with dimensions
Elevations (exterior views)
Structural engineering (often required)
Title 24 energy calculations

Step 3: Permit Submission

Submit your plans to your local building department. California requires cities to:

Accept applications ministerially (no discretionary review)
Provide feedback within 60 days
Approve or deny within 60 days of a complete application

Step 4: Construction

Once permitted, construction typically takes 4-8 months for a detached ADU. Inspections are required at various stages:

Foundation inspection
Framing inspection
Rough electrical, plumbing, mechanical
Insulation inspection
Final inspection

ADU Costs in California

ADU Type	Typical Cost Range	Cost Per Sq Ft
Garage Conversion	$100,000 - $200,000	$250 - $400
Detached New Build	$150,000 - $350,000	$300 - $500
Prefab/Modular	$100,000 - $250,000	$200 - $400
JADU (within home)	$50,000 - $100,000	$150 - $250

Additional costs to budget for:

Permit fees: $5,000 - $15,000 (impact fees now capped for ADUs under 750 sq ft)
Architectural/engineering plans: $5,000 - $15,000
Utility connections: $5,000 - $20,000
Site work and landscaping: $5,000 - $25,000

Impact Fee Exemptions

California exempts ADUs under 750 square feet from impact fees. Larger ADUs have impact fees proportionally reduced based on the ADU's size relative to the primary dwelling.

Recent Legislative Changes (2024-2025)

California continues to update ADU laws. Recent changes include:

AB 1033 (2023): Allows ADUs to be sold separately as condominiums in participating cities
AB 976 (2023): Extended the prohibition on owner-occupancy requirements until 2030
SB 897 (2022): Increased height limits to 18-25 feet in many cases
AB 2221 (2022): Streamlined permit processes and reduced delays

ADU Financing Options

Financing an ADU has become easier with several options:

Home Equity Line of Credit (HELOC): Uses existing home equity
Cash-out refinance: Refinance primary mortgage and extract equity
Construction loan: Short-term loan that converts to permanent financing
ADU-specific loans: Some lenders now offer loans specifically for ADU construction
CalHFA ADU Grant: Up to $40,000 for eligible homeowners (when funded)

Working with Cal Coast Construction

Cal Coast Construction provides full-service ADU construction across San Diego, Ventura, and San Luis Obispo Counties. Our services include:

Free site assessment and feasibility analysis
Design services or coordination with your architect
Complete permit processing
Full construction management
Utility coordination
Final inspection and certificate of occupancy

California ADU Laws: The Complete Homeowner's Guide