Types of ADUs and ADU Permits in California

What Is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary housing unit located on the same lot as a single-family or multifamily home. ADUs are legally recognized dwellings with a kitchen, bathroom, and separate entrance. They are governed by state laws (like SB 9, AB 68, and AB 1033), as well as local zoning ordinances.

🏘️ Types of ADUs in California

1. Detached ADU

A stand-alone structure separate from the main house
Often built in the backyard or rear of the property
Maximum size: Typically up to 1,200 sq ft, depending on local codes
Most expensive type, but offers privacy and rental income potential

2. Attached ADU

Built as an expansion or extension of the primary home
Shares a wall with the main dwelling
Must have its own entrance and living amenities
Size usually limited to 50% of the primary home’s size, up to 1,200 sq ft

3. Basement Conversion ADU

Converts a finished or unfinished basement into an independent unit
Requires proper egress, ventilation, and waterproofing
Subject to the same permit and code requirements as other ADUs

4. Garage Conversion ADU

Converts an existing garage into a living unit
Typically the cheapest option since the structure already exists
Parking waivers often available under California law
Must meet fire safety and energy standards (Title 24)

5. Junior ADU (JADU)

A smaller unit (up to 500 sq ft) created within the main home
Must include a basic kitchen and separate entrance
May share a bathroom with the primary residence
Often exempt from certain fees and faster to permit

📝 What Permits Are Required for ADUs in California?

1. Building Permit

Required for all ADU types, including new builds and conversions
Ensures compliance with California Building Code (CBC)

2. Planning or Zoning Permit

Needed if your project impacts setbacks, lot coverage, or height
Some cities have ADU-specific ordinances

3. Electrical, Plumbing, Mechanical Permits

Required if new systems are installed or existing ones are modified

4. Fire and Safety Approval

Particularly important for garage and basement conversions
May include smoke alarms, sprinklers, and egress windows

5. Utility Connection Approvals

Sewer, water, and electric hook-ups must be reviewed
Impact fees are waived for ADUs under 750 sq ft

🕒 How Long Does It Take to Get an ADU Permit?

Standard timeline: 30–60 days (state-mandated review period)
Plan preparation: 2–4 weeks
Inspections & revisions: 1–2 weeks after plan approval

💸 How Much Do ADU Permits Cost in California?

Permit Type	Estimated Cost (2025)
Building Permit	$1,500 – $6,000
Plan Review Fees	$500 – $2,000
Utility Hookup Fees	$0 – $5,000 (waived in many cases)
School Impact Fees	Exempt for ADUs ≤ 750 sq ft
Total Estimated Cost	$3,000 – $15,000

✅ Benefits of Building a Permitted ADU

Legal rental income
Increased property value
No risk of code violations or fines
Easier refinancing or resale
Access to incentives, grants, and tax breaks]

FAQ

Do I need a permit for all types of ADUs in California?

Yes. Whether you’re building a detached unit or converting your garage, permits are mandatory under California law.

What is the difference between an ADU and a JADU?

An ADU is a fully independent unit, while a JADU is a smaller unit (≤ 500 sq ft) within the main house, often sharing some facilities like a bathroom.

Can I build more than one ADU on my property?

Yes. California allows one ADU and one JADU on most single-family lots, and in some cases, multiple ADUs on multi-family properties.

Are ADUs under 750 sq ft exempt from fees?

Yes. California law waives impact and school fees for ADUs that are 750 sq ft or smaller.

Do ADUs require parking?

Not always. Parking requirements are waived in many situations, such as if the ADU is within a half-mile of public transit or part of a garage conversion.