Accessory Dwelling Units (ADUs) have become a cornerstone of modern housing solutions in California. With skyrocketing home prices and an ongoing housing shortage, ADUs offer a smart and flexible way to expand living space, accommodate extended family, or generate rental income. California laws have increasingly supported ADU construction by simplifying regulations and encouraging homeowners to take advantage of their property’s potential.
If you're considering building an ADU on your property, it's essential to understand each phase of the construction journey. Here's a comprehensive step-by-step guide tailored specifically to California homeowners, outlining what to expect during an ADU construction.
Step 1: Understand California ADU Laws and Zoning Regulations
Before you even pick up a hammer or call a contractor, it's crucial to familiarize yourself with your local and state ADU regulations. California has enacted multiple laws, including SB 9, SB 13, AB 68, and AB 881, which have streamlined the ADU approval process. However, local ordinances may still have specific zoning requirements.
Key Points to Check:
● Lot size and zoning restrictions.
● Maximum and minimum ADU size (typically up to 1,200 sq ft).
● Height restrictions (often up to 16-18 feet).
● Setbacks (e.g., 4 feet from side and rear property lines).
● Parking exemptions in certain cases.
● Owner-occupancy requirements (mostly removed after 2020).
Consult your city’s planning department or a local contractor familiar with your jurisdiction to verify the specific ADU requirements.
Step 2: Determine ADU Type and Design
There are several types of ADUs, and choosing the right one depends on your property, budget, and goals:
● Detached ADU: A separate structure, often in the backyard.
● Attached ADU: Shares at least one wall with the main home.
● Garage Conversion: Repurposing an existing garage into an ADU.
● Basement Conversion: Turning an underutilized basement into living space.
● Junior ADU (JADU): A smaller ADU (up to 500 sq ft) within the primary residence.
Once you’ve selected the type, you’ll need to design the layout. Many homeowners work with an architect or designer who understands California code and can help maximize space while maintaining comfort and functionality.
Design Considerations:
● Natural light and ventilation.
● Privacy for both main home and ADU occupants.
● Kitchen and bathroom layout.
● Storage solutions.
● Sustainable and energy-efficient materials.
Step 3: Hire the Right Professionals
The success of your ADU project depends heavily on hiring the right team. Here are some key professionals you may need:
● Architect or Designer: To draft plans and ensure code compliance.
● Structural Engineer: Especially important if modifying an existing structure.
● Contractor or Builder: Choose a licensed and experienced general contractor.
● Surveyor: To confirm property boundaries, if required.
● Permit Expediter: Optional but useful for navigating city bureaucracy.
Before hiring anyone, check their credentials, insurance, references, and prior ADU projects.
Step 4: Secure Permits and Approvals
Permits are a critical part of ADU construction and vary slightly by city. In California, many jurisdictions are required to approve ADU permits within 60 days of receiving a completed application.
Typical Permit Requirements:
● Site plan and floor plans.
● Structural and architectural drawings.
● Title 24 energy calculations.
● Fees and development impact charges (often reduced or waived).
Cities like San Jose, Oakland, and San Francisco often have online permitting portals, making the process more streamlined. Be prepared to revise your plans based on city feedback.
Step 5: Site Preparation and Foundation Work
Once your permits are approved, your contractor will begin site prep. This includes:
● Clearing the site of debris and vegetation.
● Setting up temporary utilities and fencing.
● Excavating the land and grading if needed.
Depending on your ADU type, different foundation options are available:
● Slab-on-grade: Most common for new builds.
● Raised foundation: Allows for crawl space and easier plumbing access.
● Pier and beam: Less invasive but less common.
Inspections may be required during this phase to ensure proper grading and drainage.
Step 6: Framing and Structural Work
With the foundation set, the ADU will start to take shape. This phase includes:
● Framing the walls, floors, and roof.
● Installing windows and exterior doors.
● Roof sheathing and weatherproofing.
Local building inspectors will likely visit to ensure structural components meet California Building Code requirements. Inspections at this stage help avoid costly changes later.
Step 7: Mechanical, Electrical, and Plumbing (MEP)
This phase involves the installation of core systems that will power and service your ADU:
● Electrical Wiring: Placement of outlets, switches, and lighting.
● Plumbing: Water lines, drains, and sewer hookups.
● HVAC Systems: Ductwork, mini-splits, or radiant heating.
California Title 24 mandates certain energy efficiency standards, so be sure that your systems and appliances comply. This step also includes rough-in inspections before drywall goes up. Step 8: Insulation, Drywall, and Interior Finishes
Once MEP systems are inspected and approved, the next phase is to close up the walls:
● Insulation: Usually spray foam, batt, or blown-in insulation. California code requires specific R-values.
● Drywall Installation: Followed by taping, mudding, and sanding.
● Interior Finishes: Paint, flooring (hardwood, vinyl, or tile), trim, cabinetry, and countertops.
Choose materials that balance style, durability, and cost. Sustainable materials are highly encouraged and may qualify for local incentives.
Step 9: Fixtures, Appliances, and Final Systems Hookup
Now your ADU is starting to look like a livable space. Time to add the final touches:
● Kitchen Fixtures and Appliances: Sink, stove, refrigerator, microwave, etc.
● Bathroom Fixtures: Toilet, sink, shower, and/or tub.
● Lighting and Electrical Fixtures: Light fixtures, ceiling fans, smoke detectors.
● Utility Hookups: Final connections to water, electricity, gas, and sewer.
Make sure all systems are tested and functional. A final inspection will ensure code compliance.
Step 10: Final Inspection and Certificate of Occupancy
Your local building department will conduct a final walkthrough to verify that everything is up to code. They will check:
● Structural integrity.
● Electrical and plumbing systems.
● Safety features (smoke alarms, fire egress, handrails, etc.).
● Compliance with the original approved plans.
Once passed, you’ll receive a Certificate of Occupancy, officially allowing you to rent out or inhabit the ADU.
Step 11: Landscaping and Exterior Work
The final stage includes beautifying the space and integrating it into your property:
● Driveways and Walkways: Ensure accessibility.
● Fencing and Privacy Screens: Maintain separation between units.
● Landscaping: Native plants, low-water lawns, and raised garden beds.
● Outdoor Lighting: Solar-powered or motion-sensor options.
California’s drought-conscious approach means choosing xeriscaping or drip irrigation systems.
Step 12: Renting or Moving In
With the ADU complete, you can now decide how to use it:
● Rental Income: Many Bay Area homeowners use ADUs for long-term or short-term rentals (check local STR regulations).
● Family Housing: Ideal for elderly parents, adult children, or caregivers.
● Personal Use: A home office, studio, or guest house.
If you plan to rent it out, familiarize yourself with California’s landlord-tenant laws and register with any required city programs.
Conclusion: Building Smart, Living Smart
Building an ADU in California is a practical, forward-thinking way to increase your property’s functionality and value. While the process involves multiple steps, being informed and working with experienced professionals will ensure a smoother journey from concept to completion.
At Aziz Construction, we specialize in ADU development and can guide you through each phase—design, permitting, construction, and final inspection. Contact us today to get started on your custom ADU solution and unlock the full potential of your property.
