Building an Accessory Dwelling Unit in California is one of the most practical ways to add space, increase property value, and create long-term flexibility. For many homeowners, the most confusing part of the journey begins before construction even starts: the permitting process. The good news is that California has worked hard to simplify the path for homeowners who want to build ADUs. With a clear understanding of the rules and the right preparation, the process can move smoothly from design to final approval.

This guide explains the full ADU permitting journey from start to finish. Whether you are designing a backyard cottage in Santa Cruz, converting a garage in San Jose, or adding a rental unit in Los Gatos, you will find each step explained in detail to help you move forward with confidence.

Understanding California’s ADU Laws

California’s statewide ADU laws were created to help ease the housing shortage and to make approvals faster and more predictable. These laws apply across every city and county, although each area can still add its own design and safety requirements. Under these statewide rules, ADUs must be approved through a simple and ministerial review process, which means your application must be accepted if it meets all relevant standards.

New regulations like AB 68, AB 881, and SB 13 have removed many of the delays that once made ADU projects difficult. Cities are now required to approve or deny an ADU permit within sixty days after receiving a complete application. Homeowners are no longer limited by strict minimum lot sizes or lengthy public hearings, and the owner-occupancy requirement was relaxed to make building easier for everyone.

Step 1: Choose the Type of ADU You Want

Before submitting an application, take time to decide what type of ADU will best fit your home and lifestyle. A detached ADU is built as a separate structure on your property, offering privacy and independence. An attached ADU connects directly to your existing home, sharing at least one wall. A conversion ADU, such as turning a garage or basement into living space, can be the most cost-efficient option for many homeowners. Each category has its own maximum size, setback, and design rules, so it is important to understand which type aligns with your goals and your property layout.

Step 2: Check Local Zoning and Setback Standards

Even though California has simplified the process statewide, local rules still play an important role. Each city or county may have its own requirements for height limits, roof design, exterior finishes, and parking. Reviewing these details early will save time later. For example, Santa Cruz County typically allows ADUs as long as the setbacks meet the minimum safety standards, which are usually four feet from the side and rear property lines. Other cities like Cupertino or San Jose may have additional design considerations for hillside or historical neighborhoods.

Joy Line Homes works with homeowners to review these requirements before any plans are drawn. This step helps confirm that the design will meet both state and local codes, ensuring the project stays on schedule once submitted for review.

Step 3: Prepare Complete ADU Plans

Once your site is confirmed to be eligible and you have selected a layout, the next step is preparing your plans. A complete ADU submittal usually includes a site plan showing property lines, setbacks, and where the ADU will be placed. It also includes detailed floor plans, exterior elevations showing height and roof pitch, structural drawings, and Title 24 energy compliance documentation. Many homeowners choose a modular or prefab builder like Joy Line Homes because the company provides permit-ready plans that already meet California Building Code standards, which can save both time and money during review.

Step 4: Submit Your Permit Application

After the plans are complete, you will submit your application to your local planning or building department. Many jurisdictions now accept digital submissions through online portals. Your submittal package typically includes a completed application form, the full set of architectural drawings, structural calculations, energy compliance forms, and applicable fees. Once submitted, your plans will go through a review process to verify compliance. If corrections are requested, you can make revisions and resubmit without starting over.

Since the process is ministerial, meaning based strictly on meeting the code rather than opinion, approval is guaranteed as long as your plans meet the rules. Most cities must respond within sixty days, though some smaller departments may take slightly longer depending on workload.

Step 5: Building Permits and Inspections

Once approved, your building permit will be issued and construction can begin. Inspections take place at specific stages to confirm the work matches the approved plans. In traditional construction, inspectors visit the site at the foundation, framing, plumbing, and final stages. In modular and prefab ADU projects, most of this inspection happens in a certified factory under controlled conditions, which means fewer site inspections and shorter build times. After final inspection, you will receive a Certificate of Occupancy, allowing you to officially use the space for living, renting, or hosting guests.

Avoiding Common Delays

There are a few issues that can slow down or complicate approvals if not handled carefully. Missing documents, incomplete drawings, or incorrect property details can cause immediate delays. Ignoring utility connection requirements or not checking homeowner association restrictions can also create setbacks. By reviewing each of these elements early, you can prevent re-submittals and keep your project on track. Joy Line Homes helps homeowners with a detailed pre-permit checklist to ensure that all materials are complete and ready for smooth submission.

Why Modular ADUs Streamline the Process

Modular construction offers one of the most efficient paths through California’s ADU permitting system. Unlike site-built projects, modular homes are constructed off-site in an HCD-approved facility. The state reviews the structural and building components during manufacturing, which means local departments only review foundation and site work. This greatly reduces review times and eliminates many of the common reasons for delay. Because the building portion is already certified at the state level, the process becomes predictable, structured, and faster for homeowners who want to move from design to delivery without waiting months for local approvals.

Joy Line Homes specializes in modular ADUs that are engineered for California’s Title 24 energy standards and designed to meet all HCD and local code requirements. Every home is planned for speed, compliance, and lasting value.

Step 6: Final Approvals and Move-In

After final inspections are complete and your Certificate of Occupancy is issued, your ADU is ready for use. Many homeowners use their new space for family members, guests, or as a rental to generate income. Others turn it into a home office or creative studio. The flexibility and long-term value of an ADU make it one of the smartest property investments available today. Once you have gone through the permitting process once, you will see how straightforward it can be with the right guidance and preparation.

Final Thoughts

California has made tremendous progress in creating a smoother ADU permitting process. Homeowners who understand the steps and prepare their plans carefully can move from concept to completion with fewer headaches. Joy Line Homes provides complete guidance throughout each phase, from feasibility review to inspection and final approval. The result is a faster, more reliable pathway to a finished ADU that adds comfort, beauty, and financial value to your property.

Whether you are exploring a compact studio ADU or a spacious two-bedroom model, Joy Line Homes helps you make sense of every permit requirement while handling the details that keep your project compliant and on schedule.