Permitting an accessory dwelling unit in California is often described as straightforward, but homeowners usually learn quickly that straightforward does not always mean fast. A permit moves through a series of checks designed to confirm zoning compliance, life safety, building code alignment, and public utility coordination. When each step is approached in the right order, permitting can feel predictable. When steps are skipped or assumptions are made, timelines stretch.

The good news is that most delays are preventable. They usually come from unclear site plans, late discovery of easements, utility questions that were not answered early, or plan sets that do not clearly show compliance. A well-prepared ADU permit set tells one consistent story from start to finish. It shows reviewers exactly what you are building, where it fits on the lot, and how it will be constructed and serviced.

This guide walks through the full permitting process from early planning to final approval, with regional context for Santa Cruz, San Jose, San Francisco, Sacramento, Santa Rosa County areas, San Luis Obispo County, Santa Barbara, Los Angeles County, Orange County, and San Diego. It also includes a strong San Jose focus, including neighborhood realities and nearby cities like Campbell, Palo Alto, and Redwood City, where homeowners often compare timelines but experience different workflows.

Step One: Confirm Your Jurisdiction and ADU Pathway

Before any design work begins, confirm whether your property is under a city jurisdiction or a county jurisdiction. This matters in many parts of California where city limits and unincorporated boundaries sit close together. It can also matter in Santa Cruz County and Santa Rosa County areas where county rules may differ from city rules even when statewide ADU law applies to both.

Next, confirm how your jurisdiction processes ADUs. Many compliant ADUs qualify for ministerial review, which is often called by-right processing. That means the project is reviewed against objective standards, such as setbacks, height, size, and building code requirements. Even in a by-right pathway, the project still must pass plan check and inspections. By-right does not mean instant. It means predictable when the documents are clear.

Step Two: Feasibility and Site Constraints

Feasibility is the phase that separates smooth permits from frustrating permits. In this phase you identify what the lot will realistically allow. Setbacks, easements, lot coverage limits, slope, and existing structures all shape what can be built and where it can be placed.

This is especially important in dense neighborhoods across San Jose, Santa Cruz, and San Francisco, where lots are tight and the buildable envelope can be smaller than expected. In parts of Sacramento and older Santa Rosa County neighborhoods, utility routing and older infrastructure can influence feasibility as much as zoning. In hillside areas of San Diego and portions of Los Angeles County, grading and drainage conditions can become a major factor.

San Jose Feasibility: Neighborhood Differences

San Jose is not one uniform permitting experience. Site realities vary across Willow Glen, Cambrian, the Rose Garden area, Berryessa, Evergreen, Almaden Valley, Downtown San Jose, and North San Jose. Side yard width, alley access, overhead utility lines, and privacy conditions vary block by block. A feasibility-first approach helps you choose a design that fits your lot rather than forcing a design and hoping it passes plan check.

Nearby cities often have different documentation expectations. Campbell, Palo Alto, and Redwood City can require a different level of detail in site plans and calculations. Even when the statewide ADU framework is similar, the local workflow can be different.

Step Three: Choose the Right ADU Type

Permitting requirements and construction complexity differ depending on whether the ADU is detached, attached, or a conversion. Detached ADUs require a clear placement strategy, new foundation work, and full utility planning. Attached ADUs involve tie-ins to the primary home and can require more structural coordination. Conversion ADUs may look simple, but they often trigger upgrades to meet current habitability standards, including insulation, egress, ventilation, and fire separation.

In compact neighborhoods like San Francisco and parts of San Jose, conversions and compact detached units often permit more smoothly than larger structures. In Santa Cruz and Santa Barbara, site and environmental factors may influence which ADU type is most practical. In Los Angeles County, Orange County, and San Diego, access and construction staging can heavily influence whether a detached unit is realistic on a given lot.

Step Four: Build a Permit Set That Makes Compliance Obvious

The permit set is the core of the approval process. Reviewers do not want to guess. They want to verify. When a plan set makes compliance easy to confirm, approvals tend to move faster and correction cycles are reduced.

Most jurisdictions require a site plan, floor plans, elevations, sections, structural plans, and Title 24 energy documentation. Mechanical, electrical, and plumbing plans are often included as well. Some jurisdictions want more detailed notes on drainage and utility connections, particularly in areas with older infrastructure or challenging site conditions.

Why the Site Plan Drives the Timeline

The site plan is often the first place a permit gets delayed. If property lines are unclear, setbacks are missing, or easements are not shown, reviewers cannot confirm zoning compliance. This triggers corrections. Corrections trigger resubmittal. Resubmittal adds time.

A strong site plan includes property lines, setbacks, easements, all existing structures, the proposed ADU footprint, distances to each property line, and clear labels. In San Jose and other high-volume jurisdictions, clarity on the site plan can shorten the process significantly because it reduces the need for back-and-forth questions.

Step Five: Address Utilities Early

Utility questions are one of the most common reasons an ADU permit slows down. Even when an ADU meets zoning standards, reviewers still need to confirm that the home will have safe electrical service, water service, sewer connection, and proper drainage management.

In older neighborhoods across San Jose, Santa Cruz, San Francisco, and Sacramento, electrical panels may be undersized and sewer lines may require confirmation of capacity or routing. In parts of Los Angeles County, Orange County, and San Diego, coordination with utilities can add time depending on service conditions. In Santa Barbara and San Luis Obispo County, certain site conditions may require additional drainage documentation.

When utilities are addressed early and documented clearly, plan check tends to focus on confirming details rather than asking foundational questions.

Step Six: Submit Plans and Enter Plan Check

After submittal, the project enters plan check. Planning verifies zoning and placement. Building reviews structural integrity and code compliance. Public works may review drainage and utility connections. Fire may review certain aspects depending on location and access.

Plan check timelines vary based on jurisdiction volume and staffing. San Jose, Los Angeles County, and San Diego often process high volumes of permits. San Francisco projects can take longer due to tight sites and layered review requirements. Santa Cruz projects may involve additional site-specific questions. Sacramento and Santa Rosa County areas may encounter infrastructure-related review questions.

Even a clean submittal usually receives plan check comments. The goal is to respond well and keep the project moving.

Step Seven: Respond to Corrections the Right Way

Corrections are part of the process, not a sign of failure. The key is how they are handled. Delays often come from slow response times or partial responses that require multiple cycles. Another common issue is making changes on one sheet but forgetting to update other sheets. That creates inconsistencies that lead to more corrections.

A strong correction response includes a clear explanation of what was changed, updated drawings, and coordinated updates across architectural, structural, and energy documents. When reviewers can confirm that every comment was addressed, the project can move toward approval without unnecessary backtracking.

Step Eight: Permit Issuance and Pre-Construction Readiness

Once plan check is complete and corrections are approved, the jurisdiction issues the permit. This step includes paying fees, receiving the stamped plan set, and confirming any pre-construction requirements. At this stage, homeowners can finalize contractor scheduling, order long-lead items, and prepare the site for construction.

Factory-built and modular ADUs often benefit from early coordination. When a design is already engineered and well-documented, it can reduce confusion during plan check and support a cleaner transition from permit issuance to build sequencing. Method alone does not determine permitting speed, but coordinated documentation often helps.

Step Nine: Inspections and Final Approval

Permitting does not end at permit issuance. Inspections are the phase where the city confirms the ADU is built according to the approved plans. Typical inspections include foundation, framing, electrical, plumbing, mechanical, insulation, and final inspection. If a discrepancy is found, it must be corrected before the project can continue.

Final approval occurs when all inspections pass and the ADU is approved for occupancy. Projects that maintain alignment between plans and construction tend to reach final approval faster because they avoid rework and inspection scheduling issues.

Regional Considerations That Affect the Permitting Journey

Across California, the process structure is similar, but the conditions and workflows vary. Santa Cruz and Santa Barbara projects may involve site and environmental context. San Francisco projects often require careful planning due to density. Sacramento projects may encounter older infrastructure and utility questions. Santa Rosa County areas can vary depending on neighborhood and existing site conditions.

In Southern California markets like Los Angeles County, Orange County, and San Diego, permit volume and construction logistics often influence timelines. Planning early and submitting clear documents is the best way to reduce delays.

Closing Guidance

Permitting an ADU is a step-by-step process that becomes far easier when homeowners approach it in the right order. Start with feasibility. Confirm constraints. Choose an ADU type that fits the site. Build a plan set that makes compliance obvious. Address utilities early and respond to corrections quickly and thoroughly.

Whether you are permitting an ADU in San Jose, Campbell, Palo Alto, Redwood City, Santa Cruz, San Francisco, Sacramento, Santa Rosa County areas, San Luis Obispo County, Santa Barbara, Los Angeles County, Orange County, or San Diego, the same principle applies. Clear planning creates predictable approvals. Predictable approvals lead to better builds and better long-term value.

A Practical Timeline Mindset

Homeowners often focus on the approval date as the finish line, but permitting is a phase that can be used productively. During plan check, you can finalize finish selections, coordinate financing, plan construction access, and prepare for inspections. When the permit is issued, you are ready to build without losing momentum.

Why City Differences Matter

ADU permitting is shaped by local workflow even under statewide law. A project in San Jose may move differently than a similar project in Campbell, Palo Alto, or Redwood City due to staffing, permit portals, and review culture. Understanding that difference helps set realistic expectations.

How to Reduce the Most Common Delays

The biggest delay drivers are unclear site plans, hidden easements, unresolved utility questions, and slow responses to corrections. A feasibility review, a clean permit set, and fast coordination typically reduce correction cycles and shorten the overall timeline.

A Better Goal Than Speed

Fast permits are nice, but predictable permits are better. When you understand the steps and plan for each one, the process becomes manageable. That clarity supports better design choices and a stronger finished ADU.

Final Perspective

An ADU should feel like a real home, and the permitting process is part of building that foundation. When your plans are aligned with your site and your documents are clear, the permit path becomes a sequence of steps rather than a guessing game.