ADU Permits in Los Angeles: What the Process Actually Looks Like

Most ADU projects that go badly do not go badly during construction. They go badly during permitting, because the design was drawn before anyone confirmed what the parcel would allow.

Confirm jurisdiction first

The single most useful thing you can do on day one is establish who reviews your project. If your address sits inside city limits, that city's building department handles it. If you are in an unincorporated pocket, the county does. Los Angeles County alone holds dozens of incorporated cities plus substantial unincorporated area, and the process is not portable between them.

People get this wrong more often than you would expect, usually because a mailing address says one city while the parcel sits outside it.

What state law settles

California ADU law applies everywhere in the state and has removed several of the obstacles that used to kill these projects. It sets baseline protections around whether a jurisdiction can refuse an ADU outright, and it constrains some of the requirements a city can impose.

What it does not do is make every local rule vanish. Setbacks, height, lot coverage, design standards, and parking still vary. So does whether a second unit triggers review that an interior remodel would not. Treat state law as the floor and your local department as the specifics.

Junior ADUs are a different animal

A junior ADU is carved out of the existing house, is smaller than a standard ADU, and has its own rules, including around the kitchen and whether it shares a bathroom with the main dwelling. It is often the fastest route to a rentable unit for people who do not need a full second dwelling. It is also frequently overlooked because homeowners assume ADU means a separate building in the yard.

The drawings you will need

Expect to produce, at minimum:

• A site plan showing the parcel, existing structures, the proposed unit, and setbacks
• Floor plans and elevations
• A foundation plan, engineered where the soils or slope require it
• Electrical, plumbing, and mechanical layouts
• Title 24 energy compliance documentation
• Structural calculations, depending on scope

A conversion generally needs less than a detached new build, but it still needs enough to show that what already exists meets current requirements for a dwelling.

Where projects actually stall

Utility capacity. A plan set that does not resolve how the second unit gets power, water, and sewer will come back. Establish panel capacity and sewer lateral capacity before design, not during review.

Setbacks discovered late. Designing to the footprint you want and then discovering the setback is a rework of the entire drawing set.

Fire access and defensible space. In or near a mapped high fire hazard area, exterior assemblies and access requirements change. Confirm the current mapping for your parcel before design.

Overlays. Historic districts, coastal zone, and hillside designations each add a layer. None of them are obstacles if you know about them at the start. All of them are expensive if you find out at plan check.

What to ask your building department before you draw anything

• Which agency has jurisdiction over this parcel
• What setbacks, height, and lot coverage apply to a second unit here
• Whether the parcel carries any overlay: historic, coastal, hillside, fire
• Whether a junior ADU is a better fit for what I want
• What the submittal package needs to include

Five questions, one phone call. It is the cheapest hour in the entire project.

Who handles this

On our projects we prepare the plans, submit the applications, and schedule the inspections. You should not be the one standing at a permit counter trying to interpret a correction notice. Ask any contractor you are considering whether permitting is included in their scope or billed separately, and get the answer in writing.