ADUs in LA & OC: What You Really Need to Know

Building an Accessory Dwelling Unit (ADU) in California is one of the most effective ways to add value to your property - whether you're creating rental income, adding space for family, or planning for multigenerational living. But navigating the process isn't always simple, especially with each county and city having its own specific regulations.

In this article, we’ll walk you through everything you need to know to build an ADU in Los Angeles or Orange County—from zoning laws to permits, parking, and setbacks. Whether you're a homeowner planning your first project or a real estate investor exploring options, this guide breaks it down in plain language while still covering all the key technical details.

Step 1: Check Your Zoning and Lot Eligibility

Before diving into design or construction, the first thing you need to verify is whether your property is eligible for an ADU.

California state law generally allows ADUs on any residential lot that has an existing or proposed single-family or multi-family dwelling. That means if you have a house or duplex, you can likely build an ADU—but local zoning rules still apply.

In Los Angeles:

If your property is within Los Angeles City, check with the Los Angeles Department of Building and Safety (LADBS). The city allows ADUs in most residential zones, but areas like the Hillside Zone, Coastal Zone, or neighborhoods with a Specific Plan Overlay may have additional layers of approval. For example, a property in the Venice area may require review by the California Coastal Commission, which adds time and complexity.

In Orange County:

Orange County has more variation because each city—like Irvine, Anaheim, Santa Ana, or Huntington Beach - has its own municipal code. While state law supersedes some restrictions, certain cities still enforce design guidelines, architectural reviews, or site constraints. If your home is in an unincorporated area, the Orange County Planning Department handles your case directly.

Step 2: Understand the Size Limits

How big can your ADU be? It depends on your lot, the type of ADU, and whether it's attached or detached.

State Law (Minimum Allowance):

• Detached ADUs: Up to 1,200 sq. ft.

• Attached ADUs: Up to 50% of the primary home’s floor area

• Junior ADUs (JADUs): Max 500 sq. ft. (must be within existing home, like a garage or bedroom)

Local Differences:

• Los Angeles typically allows up to 1,200 sq. ft. for detached ADUs with height limits around 16–25 feet, depending on your lot’s slope and zone.

• Orange County cities may limit size more conservatively. For instance, Irvine caps ADUs at 850–1,000 sq. ft. depending on the number of bedrooms, and height is often limited to 16 feet, unless you're further from the property line or have a large enough lot.

Tip: Even if you want a smaller unit (say 600–800 sq. ft.), it’s best to know your maximum buildable area first, and then scale back based on your budget and needs.

Step 3: Setback Requirements

Setbacks refer to the distance your ADU must be from the property lines.

State Rules:

• ADUs must maintain a minimum 4-foot setback from the rear and side property lines.

• If you're converting an existing structure—like a detached garage—you may not need to comply with setbacks at all.

What Counties Say:

• Los Angeles enforces additional front yard setbacks, and if you're building a 2-story ADU or located in a fire hazard zone, you may need a larger buffer or to provide reports like a soil study or geotechnical analysis.

• In Orange County, each city sets its own rules. For example, Costa Mesa sometimes requires 10 feet between the main home and the ADU. Also, check for easements, especially in tract neighborhoods—they often limit where you can build.

Step 4: Parking – Do You Need It?

This is one of the most common concerns for homeowners.

The Good News:

California law eliminates parking requirements for ADUs if:

• Your property is within ½ mile of public transit

• The ADU is built within an existing structure (e.g., a garage)

• You're in a historic district or car share area

The Catch:

• In Los Angeles, parking is usually not required, but if you’re converting a garage, you may need to replace parking elsewhere on the lot.

• In Orange County, it depends. Some cities still require 1 off-street parking space per bedroom unless you're exempt due to proximity to transit. If your lot doesn't have a driveway or space, this can become a challenge.

Step 5: Design & Building Codes

ADUs must meet California Residential Code just like any new home:

• Separate entrance required

• Kitchen with sink, cooking appliance, fridge

• Bathroom with toilet, sink, and shower/tub

• Egress windows in sleeping areas

• Hardwired smoke and carbon monoxide detectors

• Fire sprinklers only required if the main house already has them

Pro tip: The design should match or complement your main home. In places like Santa Monica or Laguna Beach, cities require architectural harmony—so plan on matching materials, roof lines, and exterior color palettes.

Step 6: Permit Process – What to Expect

Every ADU project must go through plan review and permit approval. Expect to submit:

• Site Plan

• Floor Plans

• Elevations

• Title 24 Energy Calculations

• Structural Plans (if building new)

• Sewer/Utility connection plans

In Los Angeles:

You can apply through the LADBS ADU Portal, and there’s even a Standard Plan Program that speeds up approval if you use a pre-approved design.

Timeline: 2–4 months (longer for hillside or special plan zones)

In Orange County:

Submit plans through your city’s building department. Some cities allow online submittals, but others still require hard copies and in-person appointments.

Timeline: 3–6 months depending on city, complexity, and plan revisions

Step 7: Utility Connections & Fees

Your ADU will need to connect to:

• Sewer line

• Water main

• Electric panel (shared or separate)

Most cities allow a shared utility connection, but you can request separate meters—just keep in mind that this can add $5,000–$15,000+ to your budget.

Some cities also charge Sewer Capacity Fees or School Impact Fees (usually waived for units under 750 sq. ft., per state law). Always check with the local utility providers for release forms or inspections.

Step 8: Construction & Final Inspection

Once plans are approved and fees are paid, you're ready to build. Most ADUs take 4 to 8 months to construct, depending on the size and complexity.

At the end, your city will schedule a final inspection, including:

• Structural

• Electrical

• Plumbing

• Life safety (egress, detectors, address numbers)

After passing, you’ll receive a Certificate of Occupancy—only then is your ADU legally habitable.

Final Thoughts: Build Smart, Build Legal

Building an ADU in California, especially in Los Angeles or Orange County, is a smart investment—but it’s also a regulated process. Navigating local zoning codes, permit departments, and utility requirements takes careful planning.

If you're thinking of building, talk to a licensed general contractor who knows your city’s ADU policies inside and out. At First Round Construction, we’ve helped homeowners throughout Southern California bring their ADU projects to life—from garages to guest houses and everything in between.

Need help getting started? Contact us for a free consultation.