Building an Accessory Dwelling Unit (ADU) in California offers homeowners a practical way to add living space, boost property value, and support flexible lifestyles. However, understanding the rules and requirements can be challenging. Each city has its own zoning regulations, lot size restrictions, and permitting steps. For residents of Santa Clara, Campbell, Cupertino, Milpitas, Saratoga, and Los Gatos, knowing how to navigate this process efficiently can make the difference between a smooth project and costly delays.

Joy Line Homes specializes in simplifying the ADU building process. With a deep understanding of California’s evolving ADU laws, the team helps homeowners move from concept to completion with clarity and confidence. This guide explains the regulations, permits, and best practices to follow when building an ADU in California.

1. Understanding What Qualifies as an ADU

An Accessory Dwelling Unit is a secondary housing structure located on the same property as a primary residence. ADUs can take many forms, such as detached backyard homes, attached additions, garage conversions, or interior units. California law recognizes several types of ADUs, including Junior ADUs (JADUs), which are smaller units built within an existing home.

For homeowners in Cupertino or Campbell, an ADU might serve as a rental unit, guest home, or living space for family members. Joy Line Homes designs modular ADUs that meet all state and local definitions, ensuring compliance from the start of planning.

2. State Laws Supporting ADU Construction

California has passed a series of laws to make it easier for homeowners to build ADUs. These include measures that reduce permitting times, lower fees, and override restrictive local zoning. Recent legislation such as SB 9 and AB 68 has opened the door for faster, more flexible ADU approvals across the state.

Key statewide benefits include:

• ADUs are allowed on most single-family and multifamily lots.
• Local agencies must approve permits within 60 days of submission.
• Parking requirements are reduced or eliminated near public transit.
• Impact fees are waived for ADUs under 750 square feet.

Joy Line Homes keeps up with these laws, helping clients in Santa Clara and Milpitas streamline applications under current state guidelines.

3. Local Regulations in Santa Clara County Cities

While California sets broad ADU standards, cities like Saratoga and Los Gatos enforce specific requirements related to lot size, setbacks, and height limits. Here is a summary of what homeowners should expect:

• Santa Clara: Allows detached ADUs up to 1,200 sq. ft. with reduced setbacks near rear property lines.
• Campbell: Supports attached or detached ADUs on residential lots with flexible parking rules.
• Cupertino: Encourages ADUs through expedited review and utility connection fee reductions.
• Milpitas: Permits ADUs on both single-family and multifamily lots with design standards.
• Saratoga: Focuses on maintaining neighborhood aesthetics with design review guidelines.
• Los Gatos: Allows ADUs in hillside areas under specific slope and setback limits.

Understanding these differences helps homeowners design ADUs that meet both state and city requirements from the start.

4. Zoning and Lot Requirements

Before construction begins, zoning determines where an ADU can be placed. Most single-family lots are eligible, but homeowners must verify property boundaries, access points, and existing structures. Cities like Campbell and Cupertino require setbacks ranging from 4 to 10 feet from property lines.

Joy Line Homes conducts thorough site evaluations to confirm feasibility and ensure all design plans align with zoning codes. This eliminates costly redesigns later in the process.

5. Permitting Steps for ADU Construction

The permitting process involves several stages, from design approval to final inspection. While the specific steps vary by city, most California homeowners will go through the following phases:

1. Pre-application consultation with planning staff
2. Site survey and design preparation
3. Submission of architectural plans
4. Permit application and review (within 60 days by law)
5. Building permit issuance
6. Construction and inspections

In many cases, Joy Line Homes manages these steps for clients, coordinating directly with city officials to ensure fast and compliant approvals.

6. Common ADU Design and Size Limits

Most California cities allow detached ADUs up to 1,200 square feet, though smaller lots may have lower limits. Attached ADUs are often restricted to 50 percent of the size of the main home. Two-story ADUs may require design review or privacy screening, especially in residential neighborhoods.

Joy Line Homes offers customizable modular ADU layouts ranging from 400 to 1,200 square feet, designed to meet both family needs and city standards while maintaining a modern architectural style.

7. Parking and Access Regulations

Parking is one of the most discussed aspects of ADU development. California law prohibits cities from requiring parking for ADUs built near public transit or within existing structures such as garages. If off-street parking is required, it can be placed in tandem on a driveway or setback area.

Joy Line Homes helps homeowners in busy areas like Santa Clara and Cupertino identify parking solutions that comply with city codes while keeping the property layout efficient and visually appealing.

8. Utility Connections and Energy Requirements

ADUs must comply with state building codes for energy efficiency, plumbing, and electrical systems. Detached units usually require new utility connections, while attached ADUs can share existing lines with the main home. California’s Title 24 standards also apply, ensuring energy-efficient systems throughout the property.

Joy Line Homes integrates modern utility infrastructure, including solar-ready roofs and high-performance HVAC systems, helping homeowners meet sustainability and cost-saving goals while satisfying local regulations.

9. Permit Fees and Cost Expectations

Permit fees vary depending on size, design, and location. Smaller ADUs under 750 square feet are often exempt from impact fees, which can save thousands of dollars. Typical fees include planning review, building permit, and utility connection costs.

Joy Line Homes assists clients in preparing accurate cost breakdowns early in the process to prevent surprises later. By streamlining paperwork and coordinating with local officials, they ensure each project stays on budget and on schedule.

10. Timelines and Approval Efficiency

Thanks to California’s streamlined ADU laws, local agencies must approve complete applications within 60 days. This makes it possible to move from planning to construction faster than traditional housing projects. However, incomplete applications or noncompliant designs can still cause delays.

Joy Line Homes minimizes risk by preparing all documents to meet city-specific standards before submission, ensuring homeowners experience a smooth, timely process from start to finish.

11. Common Challenges and How to Avoid Them

While regulations have become more flexible, homeowners may still face challenges such as utility coordination, neighborhood design restrictions, or limited lot space. The best way to avoid setbacks is to work with experienced ADU professionals who understand both modular construction and local compliance requirements.

Joy Line Homes has completed numerous ADU projects across Santa Clara County, leveraging its expertise to resolve zoning issues and accelerate permitting.

12. Preparing for Inspections and Final Approval

Once construction is complete, final inspections confirm compliance with building codes and approved plans. Inspections typically cover electrical systems, plumbing, structure, and energy efficiency. Joy Line Homes coordinates inspection schedules to ensure all stages meet local requirements, helping homeowners achieve final sign-off quickly.

After receiving the certificate of occupancy, your new ADU is officially ready for use or rental, marking the successful completion of the permitting journey.

Conclusion: Simplifying ADU Permitting with Joy Line Homes

California’s ADU laws have made it easier than ever to create functional, affordable, and sustainable living spaces. However, understanding each step of the permitting process remains essential for success. Joy Line Homes guides homeowners through every stage, from initial site analysis to final approval, ensuring compliance with local and state standards.

Whether in Santa Clara, Campbell, Cupertino, Milpitas, Saratoga, or Los Gatos, Joy Line Homes helps families turn their property potential into reality. By combining modern design with regulatory expertise, they make building an ADU a straightforward and rewarding experience for every California homeowner.