Permitting an ADU in Southern California: What Homeowners Need to Know

kayla5523
Aug 27, 2025
6 min read

If you’re thinking about building an Accessory Dwelling Unit (ADU) in Southern California, one of the first hurdles you’ll need to clear is permitting. Whether you’re in Los Angeles or planning a backyard build in Ventura County, understanding the rules, timelines, and required documents can make or break your project.

Permitting is more than just paperwork. It’s the legal backbone of your entire ADU process. It affects how you design your unit, how long construction takes, and how much you’ll end up paying.

In this guide, we’ll walk you through what every homeowner needs to know about ADU permits in Los Angeles, ADU regulations in Ventura County, and the key building codes that apply across Southern California.

Why Permitting Matters

The permit stage is where dreams meet reality. A well-handled permit process can fast-track your build and help you avoid costly surprises. A poor one? It can delay your project for months or lead to penalties down the line.

Getting a permit:

Ensures your ADU complies with local safety and zoning rules
Protects your home’s value and resale potential
Avoids legal issues that could arise from unpermitted construction

Every city and county handles permitting a little differently. That’s why it’s important to understand the rules in your area.

The General ADU Permitting Process in Southern California

While each jurisdiction has its own steps, most permitting processes include the following stages:

Site Evaluation
- Does your lot qualify for an ADU?
- Are there any existing code violations or encroachments?
Design Development
- Floor plans, elevations, and structural drawings must be drafted
- Site plans must show setbacks, access paths, and utility connections
Submittal to the Local Building Department
- You submit your permit application package for review
- This may include architectural drawings, energy calculations, title 24 compliance, and structural details
Plan Check & Corrections
- City or county officials review the plans
- Corrections or requests for clarification may be issued
Permit Issuance
- Once approved, you receive the permit to begin construction
Inspections During Build
- Inspections are scheduled at various stages: foundation, framing, electrical, plumbing, and final sign-off
Certificate of Occupancy
- After final inspection, your ADU is legally approved for use

How Long Does Permitting Take?

In Southern California, the ADU permitting process can take anywhere from 6 to 16 weeks or more. Timing depends on:

Your city or county’s internal processing times
How complete your initial submittal is
Whether corrections are needed
If your design falls within local pre-approved standards

At Wealth Nest ADU, we handle all submittals, revisions, and city communication so you don’t have to chase down paper trails.

ADU Permits in Los Angeles: What to Expect

The City of Los Angeles has made major efforts to encourage ADU development. But it still has one of the more complex permitting processes in SoCal.

Here’s what you should know:

LA now uses an ADU Standard Plan Program, allowing you to choose from pre-approved plans to speed up the process
However, custom builds still require a full plan check
Expect to deal with both LADBS (Building & Safety) and Planning Department reviews
Historical overlays, hillside lots, or fire zones may trigger additional reviews or restrictions
Zoning Code 12.22.A.33 is the main section covering ADUs

Common delays in LA permitting include incomplete submittals, incorrect forms, and backlogs at the plan check desk. Working with a professional familiar with LA’s system is highly recommended.

ADU Regulations in Ventura County

Ventura County and its cities, including Simi Valley, Camarillo, Thousand Oaks, and Ventura, are becoming hotspots for ADU development thanks to favorable zoning and increased demand for multi-generational housing and rentals.

Local permitting highlights:

Most cities follow California’s baseline ADU law, but with localized interpretations
Setbacks are typically 4 feet from side and rear property lines
Owner-occupancy requirements have been lifted in most cases
Max square footage is often 850–1,000 sq ft, depending on bedroom count and lot size
Some jurisdictions offer pre-approved ADU plan libraries, which can speed up approvals
Coastal zones or hillside areas may require extra reviews

Understanding your city’s specific process is key, even neighboring towns may differ.

Understanding ADU Building Codes

Permits don’t just depend on zoning. Your plans must meet California Building Code (CBC) requirements, including:

Foundation and structural safety: Proper reinforcement and footing depths are critical, especially on sloped lots.
Seismic design: Earthquake-resilient construction is mandatory across all SoCal jurisdictions.
Fire rating and egress: Units near property lines must meet 1-hour fire separation rules and include safe escape routes.
Electrical: ADUs must often have a separate panel, and older main panels may require upgrading to accommodate load.
Energy Efficiency (Title 24): Windows, insulation, HVAC systems, and sometimes solar panels must meet updated energy codes.
Plumbing: Must meet strict drainage, venting, and water heating standards. Tankless heaters are common in smaller units.

Failing to meet these codes can delay inspections or force costly last-minute changes. That’s why every Wealth Nest ADU includes review by licensed engineers.

The HUD Code Advantage: Faster, Cheaper, Simpler Permits

One of the biggest game changers in ADU permitting is choosing a HUD Code unit. Unlike traditional site-built ADUs, HUD Code units use building plans that are already state-approved. This means:

No Local Plan Check for the Unit Itself – Your ADU’s structural, electrical, plumbing, and foundation design (if using the state-approved foundation plan) are pre-cleared at the state level.
Fewer Professionals Needed – In many cases, you don’t need to hire an architect, structural engineer, or soils engineer for the unit itself.
Major Cost Savings – By avoiding those professional fees and extensive revisions, homeowners can save thousands before construction even begins.
Significant Time Savings – A site-built ADU can spend 4–6 months in plan check, but a HUD Code ADU may move through approvals in as little as one month.
Streamlined Reviews – Local officials only review setbacks, height, foundation, and utility connections, not the ADU’s internal design.

A HUD Code ADU can save you months of waiting, tens of thousands in fees, and countless headaches in the permitting stage. For many Southern California homeowners, it’s the smartest path to building faster and smarter.

Common Permitting Pitfalls to Avoid

Permitting can get held up for a variety of reasons. Here are the top mistakes that cause delays:

Submitting incomplete or inaccurate plans
Choosing an architect unfamiliar with local codes
Ignoring required stormwater or grading reports
Failing to disclose existing unpermitted work on your property
Overbuilding your allowed square footage or height
Skipping neighborhood notifications when required
Forgetting to check local utility setbacks

Delays can mean months of waiting and thousands of dollars lost. In some cases, homeowners have had to demolish unpermitted work or pay fines to bring their projects up to code.

Avoiding these issues starts with working with a team that knows the local process inside and out.

Frequently Asked Questions About ADU Permits

Do I need a separate address for my ADU?

Most cities issue a separate address during the final stages of the permit process, especially for rentals. It’s important for utilities and emergency services.

Can I convert an existing garage into an ADU?

Yes, garage conversions are one of the most popular ADU types. You’ll still need permits, structural evaluations, and energy upgrades.

Do I need a survey before I build?

In some cities, yes. Especially if your lot lines are unclear or close to setback minimums.

Will I need to upgrade my sewer line or water meter?

Possibly. If your home has outdated utilities, your permit may trigger required upgrades to support the new unit.

Can my HOA stop me from building an ADU?

They can add design rules, but under California state law, HOAs cannot outright prohibit ADUs.

How Wealth Nest Simplifies the ADU Permitting Process

We know the ADU permitting process in Southern California can be overwhelming. That’s why we do it for you.

When you work with Wealth Nest ADU, we:

Handle all architectural and engineering drawings
Submit to the correct city or county department
Manage corrections and communication with plan checkers
Coordinate inspections and scheduling
Ensure full compliance with ADU permits, regulations, and building codes
Offer pre-permitting consultations to identify any red flags early
Provide guidance on city-specific standards to speed up plan check approval

You’ll have a dedicated project manager who keeps everything on track, and a support team ready to answer your questions.

It’s a true end-to-end experience designed to make your ADU journey smooth and stress-free.

Final Thoughts: Permitting Doesn’t Have to Be Stressful

Permitting is the key to unlocking your ADU’s potential. Whether you’re in Los Angeles, Ventura County, or anywhere in between, getting it right sets the foundation for a smooth build.

At Wealth Nest ADU, we take care of the hard parts so you can focus on what matters: turning your backyard into a place of income, family connection, or future security.

Ready To Get Started?

Book your free consultation at www.wealthnestadu.com and let us handle the paperwork, red tape, and plan check stress for you.