Permitting is the part of the ADU journey that most homeowners fear, and that fear is usually based on uncertainty rather than reality. People hear stories about endless plan checks, confusing requirements, and shifting reviewer feedback. While permitting can feel technical, it is also highly predictable when you understand the sequence, prepare the right documents, and design within the rules from the beginning.

California has made ADU approvals more streamlined, but permitting is still administered locally. That means the experience can vary depending on where you live. Santa Cruz has its own review patterns. San Jose has its own workflow and high volume. San Francisco has unique existing building conditions. Sacramento, Santa Rosa County, San Luis Obispo County, Santa Barbara, Los Angeles and LA County, Orange County, and San Diego each have their own permitting culture, timelines, and checklists. The good news is that the underlying steps are similar across jurisdictions, and most delays come from the same few avoidable issues.

This article walks through what to expect when permitting an ADU home. It covers the stages, the documents, common review comments, and practical ways to reduce rechecks. It also includes region specific context for the cities and counties you serve, with extra focus on San Jose and nearby communities like Campbell, Palo Alto, and Redwood City.

Step One: Feasibility and Site Reality

Before you submit anything, you need to confirm that the project is feasible on your property. This step sounds obvious, but it is where many homeowners accidentally create future permit problems. Feasibility means understanding setbacks, height limits, lot coverage, utility locations, easements, and access. It also means knowing whether a detached ADU, attached ADU, garage conversion, or interior conversion is the best pathway for your site.

In dense neighborhoods of San Jose and San Francisco, the buildable envelope can be tight, and minor placement decisions can trigger major revisions later. In Santa Cruz and San Luis Obispo County, drainage and slope conditions often shape the foundation approach and site plan. In Los Angeles and San Diego, hillside access and fire related requirements can influence feasibility. Even in more open areas of Sacramento and Santa Rosa County, utility routing and existing structures can affect the plan set.

Feasibility is also about strategy. If the property is close to lot coverage limits, a conversion might avoid new coverage. If setbacks are tight, an attached ADU might fit better than a detached unit. When this decision is made early, permitting becomes faster because the project follows a clear and defensible path.

Step Two: Early Design With Permit Standards in Mind

Many permitting delays come from designs that are beautiful but not aligned with objective code standards. ADU permitting is not just zoning. It includes building code, energy compliance, and local requirements for safety and access. Early design should account for basic plan review items such as egress, smoke and carbon monoxide alarms, fire separation, window sizes, ceiling heights, ventilation, and accessibility considerations.

Designing with permit standards in mind does not reduce creativity. It reduces rework. A plan that respects the buildable envelope, coordinates structure and systems, and includes clear notes is easier for plan checkers to approve. This is especially important in high volume jurisdictions like San Jose and Los Angeles where reviewers are moving quickly and rely on clean documentation.

Why the Site Plan Is the Permit Anchor

The site plan is often the most important drawing in the entire submittal. It shows property lines, setbacks, existing structures, the proposed ADU footprint, distances, utility locations, access paths, and sometimes grading or drainage features. A weak site plan leads to the most common permit questions because reviewers cannot verify compliance.

When your site plan is clear, you remove ambiguity. In San Jose, clarity around setbacks and access can reduce rechecks. In Santa Cruz, clarity around drainage and grading can prevent follow up requests. In San Francisco, clarity around existing structures and conversion boundaries is essential.

Step Three: Submittal and Intake

Once the design and documentation are ready, the project is submitted through the local jurisdiction’s portal or intake process. The city or county will typically check that the submittal package is complete before it is routed to plan review. This is often called intake, completeness check, or pre-screen.

Completeness checks are not about approving the project. They are about verifying that all required documents are included. Missing documents can delay the start of plan review. Common missing items include a title sheet with project scope, property owner authorization forms, energy documents, structural calculations, and sometimes a soils report or stormwater notes depending on the site.

In some regions, homeowners benefit from a preliminary consultation or planning counter meeting. While not required everywhere, this can be useful for unusual sites, hillside properties, or projects involving conversions. A short conversation can clarify expectations and prevent misaligned assumptions.

Step Four: Plan Check Review and Corrections

Plan check is the formal review stage. During plan check, reviewers examine zoning compliance and building code compliance. In many jurisdictions, ADUs are processed ministerially, meaning the review is based on objective standards rather than discretionary judgment. This tends to reduce uncertainty, but it does not eliminate corrections. Corrections are normal. Most projects receive at least one round of comments.

Plan check comments usually fall into predictable categories. Zoning comments often involve setbacks, height measurement, lot coverage calculations, parking notes, and access paths. Building comments often involve structural details, fire separation, egress windows, smoke alarms, ventilation rates, and accessibility related clearances. Energy comments often involve insulation specs, window performance, and documentation alignment between plans and compliance forms.

The fastest path through plan check is to respond thoroughly and clearly. Provide revised drawings, highlight changes, and include a response letter that references each comment. Avoid partial responses. Partial responses tend to trigger another round of comments because reviewers must re-evaluate the same items.

How Timelines Usually Work

Permitting timelines vary by jurisdiction and by project complexity. A simple detached ADU on a flat lot with clear documentation often moves faster than a conversion in an older structure. High volume cities can have longer review queues. Smaller jurisdictions may review faster but still request detailed site documentation.

Across Santa Cruz, San Jose, San Francisco, Sacramento, Santa Rosa County, San Luis Obispo County, Santa Barbara, Los Angeles and LA County, Orange County, and San Diego, the most consistent driver of timeline is documentation quality. A clean set that answers reviewer questions before they ask them typically reduces total rounds of plan check.

San Jose Focus: What Makes Review Feel Different

San Jose is one of the most active ADU markets in California. Because of volume, the process tends to be structured and checklist driven. That can be a benefit when you submit a clear package. It can also feel strict if the drawings leave questions unanswered.

Neighborhood context matters. Willow Glen lots often require thoughtful privacy and placement planning. Cambrian Park and Almaden Valley may have different existing structure patterns that affect lot coverage. Evergreen and Berryessa may involve larger lots but still require clear access and utility plans. The common factor is that a strong site plan and accurate setback dimensioning reduce friction.

Nearby cities like Campbell, Palo Alto, and Redwood City operate under the same state ADU framework, but their local checklists and reviewer priorities can differ. A project that passes easily in one jurisdiction may need slight documentation changes in another, especially for conversions and privacy related window placement.

Fees, School Districts, and Utility Requirements

Permitting also includes fees. Some fees are plan check fees and permit issuance fees. Others can involve impact fees depending on unit size and local policy. Utility agencies may require separate upgrades or connections. These requirements are often separate from city plan check but can affect the schedule.

In older parts of San Francisco and Los Angeles, electrical upgrades may be common. In Santa Cruz and San Luis Obispo County, water and sewer connection details may require additional coordination. In Orange County and San Diego, utility trenching routes and exterior restoration can influence site planning.

Permit Issuance and the Path to Construction

Once all plan check comments are cleared, the jurisdiction issues the permit. At that stage, you are cleared to begin construction, but you will still need inspections. Inspections typically include foundation, framing, mechanical, electrical, plumbing, insulation, and final inspections. If the ADU is factory built or modular, there may be additional coordination steps related to delivery, foundation readiness, and set day inspections.

Planning for inspections early keeps construction moving. A permit is not the end of paperwork, but it is the milestone that turns the project into a buildable plan. Homeowners who understand this sequence feel more confident because they know what is coming next.

Factory Built ADUs and Permitting Expectations

Factory built and modular ADUs can support permitting predictability because unit dimensions and systems are coordinated earlier. When the design is stable, it is easier to verify zoning compliance and prepare clean plan sets. The site work still needs detailed documentation, especially for utilities and access, but the reduced variability can help streamline review.

Many homeowners appreciate that factory built methods can align well with the ministerial intent of California ADU policy. Less uncertainty during design can mean fewer revisions during plan check. The best outcomes still come from early envelope review and clear documentation.

Closing Perspective

Permitting an ADU home is a process, not a mystery. When you understand the sequence, prepare the right documents, and respond clearly to plan check comments, the experience becomes far more manageable. The most common delays come from unclear site plans, incomplete packages, and designs that do not align with objective standards.

Across Santa Cruz, San Jose, San Francisco, Sacramento, Santa Rosa County, San Luis Obispo County, Santa Barbara, Los Angeles and LA County, Orange County, and San Diego, homeowners who start with zoning clarity and strong documentation tend to move faster. With the right planning team, permitting becomes a predictable step toward a finished ADU that feels like a real home and delivers long term value.