The ADU Permit Process in LA County, Step by Step

Permitting an ADU in unincorporated Los Angeles County means clearing two separate approvals: Department of Regional Planning sign-off on zoning (setbacks, height, lot coverage), then a building permit through the Department of Public Works. Under a standard-plan or by-right ADU design of 750 square feet or less, that process can move in about 60 days; a fully custom design typically takes 3–6 months. If your property sits inside an incorporated city rather than unincorporated County land, that city's own building department — not LA County — handles your permit instead.

First, Confirm Who Has Jurisdiction

"Los Angeles County" covers both unincorporated areas (permitted directly by the County) and dozens of incorporated cities — Los Angeles, Long Beach, Pasadena, Glendale, and many others — each of which runs its own building department and ADU ordinance. The steps below apply to unincorporated County land, permitted through the County's Department of Regional Planning and Department of Public Works.

If your property is inside an incorporated city, check that city's building department directly — the overall ADU rules are similar statewide (California's ADU law sets the floor), but the application portal, fee schedule, and specific plan-check contact are different.

The LA County ADU Permit Process

1. Confirm zoning eligibility with Regional Planning
Before applying for a building permit, get Department of Regional Planning sign-off that your project conforms to zoning — setbacks, height limits, and lot coverage. This is submitted as a Base Application with a site-specific plot plan, and catches zoning problems before you've paid for full construction drawings.
2. Prepare your application package
A land use application, architectural plans, and current photos of the property are the baseline. Using one of the County's pre-approved ADU plan sets (rather than a fully custom design) skips a large part of this step and moves you straight into a faster review track.
3. Submit the building permit application
File a Residential New Construction Building Permit with the County, either in person at your local Building and Safety District Office or online through EPIC-LA, the County's permitting portal.
4. Plan check and completeness review
The Department of Public Works Building & Safety Division reviews the plans against building code. As of January 1, 2026, state law (SB 543) requires the County to tell you within 15 business days whether your application is complete — so you're not left waiting indefinitely to find out a document is missing. The review clock pauses each time a correction letter goes out and restarts once you resubmit.
5. Pull the permit and begin construction
Once plans are approved, you have one year from the application date to pay fees and pull the permit, or the approval can lapse (extensions are available on request). From there, inspections follow the normal building-permit schedule through final sign-off.

Realistic Timelines for 2026

A by-right ADU of 750 square feet or less, especially using a pre-approved plan set, can move through LA County review in around 60 days under the current streamlined pathway. A larger or fully custom-designed ADU more typically takes 3 to 5 months of plan check before permits are issued.

The single biggest factor that blows up a timeline isn't the County — it's incomplete or non-compliant plans. Missing structural, electrical, or zoning details trigger a correction letter, which pauses your review clock until you resubmit. A licensed contractor or designer who has been through LA County's process before is worth the fee just for avoiding that back-and-forth.

How a Licensed Contractor Handles This For You

A licensed general building contractor (CSLB Class B) who regularly builds ADUs in LA County typically prepares or coordinates the application package, knows which pre-approved plan sets clear review fastest, and can respond to a correction letter without the delay of a homeowner relaying questions back and forth between an architect and the County. That experience is usually the difference between a 60-day permit and a 6-month one.

Official LA County Resources

Go straight to the source for current requirements, fees, and pre-approved plan sets.

Frequently Asked Questions

How long does it take to get an ADU permit in LA County?

For a by-right ADU under 750 square feet using a pre-approved plan, roughly 60 days is achievable under the current streamlined pathway. A larger or custom-designed ADU typically takes 3 to 6 months of plan check.

Do I need Regional Planning approval and a building permit, or just one?

Both. Regional Planning confirms your project meets zoning rules (setbacks, height, lot coverage) before the Department of Public Works reviews the actual construction plans against building code and issues the building permit.

What happens if my property is inside a city like Los Angeles or Pasadena, not unincorporated County land?

Then that city's building department handles your permit, not LA County directly. The overall ADU rules are similar since they're set by California state law, but the application portal and specific contact will be different — check with your city's building department first.

Does using a pre-approved ADU plan really speed up permitting?

Yes. A pre-approved or standard plan set has already cleared the design-review portion of the process, so your application moves faster through plan check than a fully custom design does.

What is SB 543 and how does it affect my ADU permit?

SB 543 is a California law, effective January 1, 2026, that requires permitting agencies — including LA County — to tell you within 15 business days whether your ADU application is complete, rather than leaving you waiting with no answer on missing documents.

Skip the Permit Guesswork

A licensed ADU contractor who already knows LA County's process can save months compared to going it alone. Connect with a CSLB-verified contractor directly — no account required.

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