Permitting is where an ADU project becomes real. It is the moment your ideas turn into a plan set that must satisfy zoning, building code, and local review standards. For many homeowners, permitting also becomes the most stressful phase because it can feel like a moving target. A plan passes one checkpoint, then a new comment appears. A reviewer asks for a detail you have never heard of. Timelines stretch, and the project starts to feel heavier than expected.

Most permitting challenges are not random. They come from predictable gaps in planning, documentation, and coordination. The homeowners who move through permitting smoothly are usually not the ones with the simplest projects. They are the ones who understand what reviewers are looking for and who prepare a package that answers questions before they are asked.

This matters across California because permitting is administered locally. Santa Cruz has different site patterns than San Jose. 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 checklists and review culture. Yet the same core problems show up everywhere, and the same strategies help homeowners avoid them. This guide breaks down the most common ADU permitting challenges and the practical steps that reduce rechecks, delays, and redesigns, with a special focus on San Jose and nearby communities like Campbell, Palo Alto, and Redwood City.

Challenge One: Starting With a Floor Plan Before Confirming the Envelope

A very common mistake is falling in love with a floor plan before confirming the buildable envelope. The buildable envelope is the real space available for construction after setbacks, easements, and site constraints are applied. When the envelope is not defined early, homeowners often design an ADU that fits in theory but fails in plan check because of setback conflicts, lot coverage issues, or access requirements.

In San Jose, this can happen on narrow lots where the side yard is tighter than expected or where an existing garage sits close to the rear property line. In Santa Cruz and San Luis Obispo County, slope and drainage can influence placement and foundation design. In San Francisco, the envelope is often shaped by existing structures and conversion boundaries. In Los Angeles and San Diego, hillside access and fire related constraints can affect what looks feasible on paper.

How Homeowners Avoid It

Homeowners avoid this issue by starting with a zoning and site analysis. Confirm setbacks, height limits, lot coverage, utility corridors, and access routes before committing to a plan. A simple envelope sketch can save weeks of redesign. When the plan is designed to fit the envelope naturally, reviewers have fewer reasons to question compliance.

Challenge Two: Weak Site Plans and Missing Dimensions

Site plans are the foundation of zoning review. If the site plan is unclear, the project tends to attract comments, even if the ADU itself is compliant. Reviewers need to verify property lines, setbacks, building footprints, distances, and access paths. When those items are missing or inconsistent, the reviewer cannot confidently approve the set.

This is especially common when homeowners use informal measurements or do not account for irregular lots. In high volume areas like San Jose and Los Angeles, reviewers rely heavily on clear dimensioning because they are working quickly. In Santa Cruz and Santa Barbara, site drainage and grading notes may be closely reviewed. In Orange County and San Diego, exterior access and utility routes often matter more than homeowners expect.

How Homeowners Avoid It

Use a professional site plan with clear setbacks and distances labeled from property lines to the proposed ADU. Show existing structures, driveways, paths, and relevant utilities. Add notes that clarify scope, especially if the project includes demolition or conversion. A strong site plan reduces questions and prevents rechecks caused by uncertainty.

Challenge Three: Incomplete Submittal Packages

Many projects lose time before plan check even begins because the submittal package is incomplete. Jurisdictions typically run a completeness check, and missing documents can pause routing. Common missing items include structural calculations, energy documents, soils information when needed, owner authorization forms, and the correct plan sheets for electrical, plumbing, and mechanical scope.

In San Francisco and Los Angeles, conversion projects often require careful documentation of existing conditions and code upgrade scope. In Santa Cruz and San Luis Obispo County, geotechnical or drainage related notes may be needed for certain sites. In San Jose, small omissions can quickly trigger resubmittals because intake is checklist driven.

How Homeowners Avoid It

Request the jurisdiction’s ADU submittal checklist and match your package to it. Confirm which sheets are required for your ADU type, and ensure the title sheet clearly defines scope. If you are using a modular or factory built ADU, include the correct documentation for the unit and for site work. Completeness is one of the fastest wins in the permitting process.

Challenge Four: Title 24 and Energy Document Mismatches

Energy compliance is a frequent source of plan check comments. The most common issue is mismatch. The drawings specify one insulation value, window type, or mechanical system, while the energy forms specify another. Reviewers flag these inconsistencies because they need alignment between the compliance documents and the construction plans.

This can happen when design changes occur late, such as window resizing for privacy, HVAC changes for efficiency, or revisions to wall assemblies for sound control. It can also occur when multiple consultants are involved and documents are not updated consistently. In San Jose, Sacramento, and San Diego, energy reviewers often move quickly and will return a set if details do not match. In coastal areas like Santa Cruz, window and ventilation strategies also intersect with comfort and moisture management, which makes coordination especially important.

How Homeowners Avoid It

Lock key systems early and keep drawings and energy forms in sync. When any change is made to windows, insulation, or mechanical equipment, update both the plans and the compliance documents together. A final cross check before submittal prevents many avoidable comments.

Challenge Five: Structural and Foundation Detail Gaps

Structural comments are common, especially for conversions or additions to older buildings. Reviewers want to see how loads are carried, how foundations are designed, and how the structure meets seismic requirements. Missing connection details, unclear shear wall layouts, or incomplete footing notes can lead to significant rechecks.

In San Francisco and parts of Los Angeles, older structures often require careful evaluation. In Santa Cruz and Santa Rosa County, soil conditions and drainage may influence foundation decisions. In San Jose, the structural review is typically straightforward when calculations and details are complete, but it can become slower when the plans rely on vague notes.

How Homeowners Avoid It

Include complete structural drawings and calculations that match the architectural plans. If the project is a conversion, document existing conditions and show upgrade scope clearly. If the project is detached, ensure the foundation design is coordinated with site grading and utility routes. Clarity is the goal because it reduces back and forth.

Challenge Six: Conversion Projects and Code Upgrades

Garage and interior conversions can be cost effective, but they often trigger code upgrade questions. Reviewers may ask about fire separation, ceiling heights, ventilation, insulation, electrical capacity, and safe egress. Homeowners sometimes assume a conversion is simpler because the structure exists. In reality, conversions require careful documentation because you are transforming a non-habitable space into a dwelling.

In San Jose neighborhoods where rear garages are common, this pathway can work well when the existing structure is in good shape. In San Francisco, interior conversions may require detailed planning around stairs, egress, and existing building systems. In Los Angeles and San Diego, garage conversions are popular but still require compliance with habitable space requirements.

How Homeowners Avoid It

Treat conversions like new homes in terms of documentation. Show insulation, ventilation, egress, and fire separation clearly. Include a plan that explains the existing structure and what is changing. This approach reduces reviewer uncertainty and helps the conversion move through plan check more predictably.

Challenge Seven: Utility Coordination and Connection Surprises

Utility planning is often underestimated. Water, sewer, electrical, and gas systems can create scheduling and permitting surprises if they are not coordinated early. Some sites require panel upgrades. Others require long trench routes or complicated tie-ins. Utility agencies may have separate review processes that do not align perfectly with city plan check timelines.

In older areas of San Francisco and Los Angeles, electrical upgrades are common. In Santa Cruz and San Luis Obispo County, water and sewer routing can interact with slope and drainage. In Orange County and San Diego, exterior restoration and trench routing can influence site planning. In San Jose, high volume neighborhoods may have tight utility corridors and crowded property conditions that require clear planning.

How Homeowners Avoid It

Map utilities early and confirm connection requirements. Include utility routes on the site plan when possible. Budget for potential upgrades and plan trench restoration. When utilities are treated as part of the design rather than an afterthought, the project avoids late stage surprises.

Challenge Eight: Slow Responses to Plan Check Comments

One of the most overlooked causes of delay is the homeowner’s response approach. Some resubmittals address only part of the reviewer’s comments or revise drawings without explaining changes. Reviewers then need to re-read the set, and additional comments follow. This can create extra rounds of review that could have been avoided with clearer communication.

How Homeowners Avoid It

Prepare a detailed response letter that references each comment and explains how it was addressed. Cloud the revised drawings if required and highlight changes. Keep all documents consistent, including architectural sheets, structural sheets, and energy forms. A complete response package reduces rechecks and improves turnaround.

San Jose and Nearby Cities: Where Small Details Matter

San Jose is a strong focus market, and it is also one of the busiest. That combination makes documentation quality especially important. Neighborhoods like Willow Glen, Almaden Valley, Evergreen, Cambrian Park, and Berryessa can each present different lot patterns, existing structures, and privacy constraints. The same core permitting rules apply, but site specifics change the best strategy.

Nearby cities like Campbell, Palo Alto, and Redwood City operate under the same statewide ADU framework but have their own local checklists and reviewer priorities. Homeowners who treat each jurisdiction as unique and prepare a clean, checklist aligned set tend to move faster than those who assume one size fits all.

Why Factory Built ADUs Can Reduce Permitting Friction

Factory built and modular ADUs can reduce certain permitting challenges because unit dimensions and systems are resolved earlier. A stable plan makes it easier to confirm setbacks, height compliance, and lot coverage calculations. It also reduces the chance of late stage design changes that trigger energy document mismatches or structural rechecks.

Site work still requires careful planning, especially for utilities and access, but predictable unit design often helps homeowners stay on track. When paired with a strong site plan and clear responses to plan check comments, factory built methods can support a smoother permitting experience.

Closing Perspective

Most ADU permitting challenges come from avoidable gaps: unclear site plans, incomplete packages, inconsistent documents, and slow or partial responses to comments. The best way to avoid these problems is to start with envelope clarity, coordinate all documents, and respond to reviewers with precision.

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 plan early and document thoroughly tend to permit faster and build with fewer surprises. With the right approach, permitting becomes a manageable step toward a finished ADU that adds real long term value.