Introduction: Why ADU Building Matters in California
Building an Accessory Dwelling Unit (ADU) is one of the smartest moves a California homeowner can make today. With housing shortages at historic levels, state laws have evolved to make ADUs easier, faster, and more affordable to build than ever before.
For many families, an ADU isn’t just about extra square footage—it’s about flexibility, financial security, and long-term property value. Whether you want a rental unit, a private space for family, or simply more living options, ADUs have become one of the most homeowner-friendly housing solutions in the U.S.
At Global Arch Construction, we’ve helped dozens of homeowners across Northern California turn their ADU dreams into reality. This Q&A guide is designed to simplify the process, clear up confusion, and give you practical answers based on real experience and California law.
Understanding ADUs
What is an Accessory Dwelling Unit (ADU)?
An Accessory Dwelling Unit (ADU) is a self-contained living space located on the same property as your main home. To qualify, it must include its own:
- Kitchen
- Bathroom
- Sleeping area
In other words, it’s a second home on your property that can be fully independent from your primary residence.
Types of ADUs: Detached, Attached, Garage Conversions & More
California law gives homeowners flexibility in how they build ADUs:
- Detached ADUs: A standalone unit in your backyard.
- Attached ADUs: Built as an extension of your existing home.
- Garage Conversions: Turning an existing garage into a living unit.
- Above-Garage Units: Adding a living space above a detached garage.
- Basement Conversions: Repurposing unused space below your home.
- Manufactured Housing or Efficiency Units: Prefabricated options that meet ADU requirements.
This flexibility makes ADUs suitable for a wide variety of properties and budgets.
Benefits of Building an ADU for Homeowners
Building an ADU provides multiple benefits at once:
- Extra Living Space: Perfect for extended family, aging parents, or young adults.
- Rental Income: Generate monthly income with long-term tenants.
- Flexibility: Use it as a home office, guest house, or vacation rental.
- Property Value: Homes with ADUs often appraise higher in California.
- Smart Housing Solution: Adds housing supply in communities without requiring new land.
JADUs Explained
What is a Junior Accessory Dwelling Unit (JADU)?
A Junior Accessory Dwelling Unit (JADU) is a smaller housing option that maxes out at 500 sq. ft. and must be created within your existing home.
Typical examples include converting:
- An attached garage
- A spare bedroom or unused section of your home
- Part of an existing floor plan
When a JADU is the Right Choice
A JADU is ideal when:
- You want a low-cost starter ADU.
- You need a compact rental unit with minimal construction.
- You’re creating a private suite for a parent, in-law, or young adult.
- You’d like to add value without major property expansion.
Because JADUs use existing square footage, they’re often the fastest and most affordable way to add housing.
The 66323 Rule and Protected ADU Categories
What are “66323 Units”?
“66323 Units” come from California Government Code Section 66323. These are specific categories of ADUs and JADUs that must be approved by law.
Homeowner Rights Under Section 66323
If your project fits into one of these categories, cities and counties must:
- Approve your project ministerially (no hearings, no subjective reviews).
- Evaluate only based on objective standards like building code and safety.
- Avoid blocking projects with restrictions like lot coverage, floor-area ratio, or arbitrary design rules.
Why This Law Makes ADU Approval Easier
In plain English: if your ADU or JADU falls under 66323, the city must say yes. This protection gives homeowners confidence and prevents local governments from stonewalling ADU projects with red tape.
California ADU Law Updates (2023–2025)
California continues to strengthen ADU rights. Here are the most important recent updates:
Owner-Occupancy Rule Changes
Cities can no longer require the homeowner to live in the primary residence if they build an ADU. This means more flexibility for rental properties and investments.
Pre-Approved ADU Plans
Many jurisdictions now offer pre-approved designs that homeowners can use to:
- Reduce architectural costs
- Speed up permitting
- Avoid design disputes with planning staff
Amnesty Programs for Older ADUs
If you have an unpermitted ADU, new amnesty programs allow you to bring it into compliance without major penalties. This is a major win for homeowners who built before ADUs were legalized.
Streamlined Laws and Enforcement
ADU laws have been consolidated under Section 66323, making them easier to navigate and ensuring consistent enforcement across cities.
Bottom line: Every update since 2017 has made ADUs simpler, faster, and more affordable for homeowners.
Costs, Fees, and Utility Connections
ADU Impact Fees Explained
- 750 sq. ft. or smaller: No impact fees.
- Larger units: Fees apply but must be proportional to size.
School Fees: What You Need to Know
School districts may charge fees per square foot, but smaller ADUs often qualify for reduced or waived costs.
Utility Hookups: Shared vs. Separate
- Shared connections: Many ADUs can tap into the main home’s water, sewer, and power.
- Separate connections: Sometimes required, but cities cannot impose excessive costs.
At Global Arch Construction, we map out all possible fees upfront so there are no surprises later.
Steps to Building Your ADU in California
Site Evaluation and Feasibility Study
Every project starts with a site visit and zoning check to determine what’s possible on your property.
Design, Engineering, and Pre-Approval
Next comes design work—either custom or pre-approved plans. Structural and energy calculations are included.
Permitting Process
Applications are submitted to your local city or county. Thanks to state law, permits must be processed within 60 days for eligible ADUs.
Construction Timeline and Completion
Typical ADUs take 4–9 months from start to finish, depending on size and complexity.
What to Expect from Global Arch Construction
At Global Arch Construction, we:
- Provide feasibility studies before you commit.
- Offer transparent budgets and timelines.
- Manage the entire permit and build process.
- Deliver high-quality craftsmanship backed by experience.
Our motto: “You dream it, we build it.”
Frequently Asked Questions (FAQs)
Do I need a permit to build an ADU in California?
Yes, every ADU requires a building permit. However, state law requires cities to approve qualifying ADUs quickly.
Can I rent out my ADU long-term or short-term?
Long-term rentals are always allowed. Short-term rentals (like Airbnb) depend on your city’s rules.
How much does it cost to build an ADU in California?
Costs vary from $100,000–$350,000+, depending on size, finishes, and site conditions. JADUs are typically less expensive.
Are there size limits for ADUs and JADUs?
ADUs can be up to 1,200 sq. ft. (city rules may vary). JADUs are capped at 500 sq. ft.
How long does the ADU building process take?
On average, 4–9 months from planning to move-in, depending on project complexity.
Can I finance my ADU with a loan?
Yes. Home equity loans, construction loans, and new ADU-specific financing programs are widely available.
Making ADU Building Simple with Global Arch Construction
California has transformed ADU laws to make them one of the most homeowner-friendly housing solutions in the country. From new construction in your backyard to compact JADUs within your home, the possibilities are nearly endless.
With the right partner, the process doesn’t have to be overwhelming. At Global Arch Construction, we guide homeowners through every step—from feasibility and design to permits and construction.
👉 You dream it, we build it.
If you’re ready to explore ADU options for your property, reach out to us today and let’s make your vision a reality.
.webp)
-q80.webp)
