Fall ADU Permit Strategy Guide: Submit Now, Build in Spring

The Strategic Advantage of Fall Permit Submission

Most Bay Area homeowners think about building an ADU in the spring, submit permits in the summer, and end up breaking ground in late fall or winter, right when the rainy season makes site work difficult and expensive. There is a better approach.

Submitting your ADU permit in the fall flips the typical timeline in your favor. While your application moves through plan check during the winter months, you prepare for construction. When spring arrives with its ideal building weather, your permits are approved and your team is ready to break ground.

This is not a shortcut. It is a strategy that uses each season for what it does best: fall for design and submission, winter for review and preparation, and spring for construction.

Building codes and permit requirements change. Verify current requirements with your local building department before starting any project.

Understanding ADU Permit Timelines in the Bay Area

California law requires cities to act on ADU applications within 60 days of receiving a complete application. This provision, established by AB 68 and reinforced by subsequent legislation, was designed to prevent cities from stalling ADU projects through slow permit processing.

In practice, the keyword is “complete.” If your application is missing documents, contains code violations, or needs engineering corrections, the city issues plan check comments and the clock resets. Each round of corrections adds 2-4 weeks to your timeline.

Here is what Bay Area homeowners can realistically expect:

Faster Cities (6-10 Weeks for Clean Applications)

Cities like San Jose, Fremont, and Santa Clara have streamlined their ADU review processes. If your application is complete and code-compliant, these cities often issue permits within 6-10 weeks. They have dedicated ADU review teams and clear submission checklists.

Moderate Cities (8-12 Weeks)

Most mid-size Bay Area cities, including Sunnyvale, Mountain View, Milpitas, and Campbell, fall in this range. They process ADU permits efficiently but may have smaller planning departments that handle ADU reviews alongside other projects.

Slower Cities (10-16 Weeks)

Some cities have more involved review processes, additional design review requirements, or smaller staffing. Palo Alto, Los Altos, and Saratoga sometimes take longer, particularly for ADUs with design review overlay requirements or projects on hillside lots.

What Adds Time

Regardless of the city, these factors extend permit timelines:

• Incomplete applications: Missing a required document delays your entry into the review queue
• Code violations in plans: Setback errors, height miscalculations, or non-compliant features require redesign
• Engineering corrections: Structural calculations that do not satisfy the plan checker trigger revision requests
• Utility coordination: Some cities require utility will-serve letters before issuing permits
• Environmental review: Projects near creeks, in fire zones, or on steep slopes may trigger additional review

The Fall ADU Timeline: Month by Month

Here is how the fall permit strategy plays out over a typical ADU project.

Summer (June Through August): Design Phase

Use the summer for the design work that produces a permit-ready package. This includes:

Site assessment. A surveyor maps your property boundaries, existing structures, setbacks, and topography. This becomes the foundation for your site plan.

Soils report. A geotechnical engineer tests your soil conditions and provides foundation recommendations. This report is required for the permit application and informs the structural engineering.

Architectural design. Work with your designer or design-build firm to develop floor plans, elevations, and construction details. Make decisions about layout, materials, window placement, and exterior finishes during this phase.

Structural engineering. An engineer designs the foundation, framing, and lateral force system based on the soils report and architectural plans. The structural calculations are a required part of the permit package.

Title 24 energy compliance. A certified energy consultant prepares the compliance documentation showing your ADU meets California’s energy code.

Utility planning. Determine how your ADU will connect to water, sewer, gas, and electricity. Some ADU configurations require utility upgrades or new service connections.

September Through October: Permit Submission

With all documents complete, submit your permit application. A thorough application includes:

• Completed permit application forms
• Three to five sets of plans (check your city’s requirements)
• Structural engineering calculations
• Title 24 energy compliance documents
• Soils report
• Site survey
• Utility connection plans
• Stormwater management plan
• Any required supplemental forms (design review, tree protection, etc.)

Submit as early in the fall as your documents allow. Earlier submission means earlier approval.

November Through January: Plan Review and Corrections

Your application enters the plan check queue. During this period, plan checkers from planning, building, fire, and public works departments review your documents for code compliance.

If corrections are needed, you will receive a plan check letter detailing required changes. Respond to corrections promptly and thoroughly. Each round of revisions adds time, so address every comment in the first response rather than going back and forth.

November Through February: Productive Waiting

While the city reviews your plans, use this time to prepare for construction:

Finalize material selections. Choose siding, roofing, windows, doors, flooring, cabinetry, countertops, plumbing fixtures, and electrical fixtures. Having every material selected before construction starts prevents delays.

Order long-lead items. Windows, custom cabinetry, and specialty fixtures often have 6-10 week lead times. Ordering in December or January means everything arrives by the time construction begins.

Select and contract with your builder. If you are not using a design-build firm (which handles this automatically), interview general contractors, check references, and sign a construction agreement during winter.

Prepare the site. While you cannot do structural work without permits, you can clear vegetation, remove stored items from the building footprint, and address any drainage issues on the property.

Set up financing. If you are financing the ADU through a construction loan or HELOC, complete the application and approval process during winter so funds are available when construction starts.

March Through April: Permit Issuance and Ground-Breaking

Once all plan check comments are resolved, the city issues your building permit. With materials ordered, contractors scheduled, and the site prepared, construction begins immediately.

Spring is the ideal season for the early phases of ADU construction: excavation, foundation work, and framing. Dry weather means no rain delays for site work, concrete curing conditions are optimal, and longer daylight hours give crews more productive time each day.

Preparing a Permit-Ready Application

The quality of your permit application directly affects how quickly it moves through review. Here are the most common issues that trigger plan check corrections and how to avoid them.

Setback and Height Compliance

Every Bay Area city has specific setback and height requirements for ADUs. These vary based on lot size, zoning, and the type of ADU (attached, detached, or garage conversion). Verify the requirements with your city’s planning department before finalizing your design, not after.

Complete Structural Calculations

Plan checkers review structural engineering in detail. Incomplete calculations, missing load paths, or inadequate lateral analysis will be flagged. Use a structural engineer experienced with residential construction in your specific city.

Title 24 Accuracy

Energy compliance documentation must match the architectural plans exactly. If the plans show one type of window and the Title 24 report specifies another, the plan checker will flag the discrepancy. Coordinate between your architect and energy consultant to ensure consistency.

Fire Sprinkler Plans

ADUs that are attached to the main house or within a certain distance of property lines may require fire sprinklers. Check your city’s requirements early, as adding sprinklers after the design is complete requires redesign of ceiling layouts, water supply, and sometimes the floor plan itself.

Using Winter Months Productively

The winter months between permit submission and approval are not downtime. They are an opportunity to make your project better and faster.

Visit showrooms and select finishes. Without the pressure of an active construction schedule, you can take time to see materials in person, compare options, and make confident decisions.

Research and select appliances. For ADUs with full kitchens, appliance selection affects cabinetry dimensions, electrical requirements, and plumbing rough-in locations. Selecting appliances during winter ensures your construction team has exact specifications on day one.

Plan landscaping. Think about how the ADU integrates with your existing landscape. Decide on pathways, privacy screening, outdoor lighting, and any hardscape needed for a separate entrance.

Review your budget. With contractor bids in hand and materials priced, refine your budget to ensure you are comfortable with the total investment before breaking ground.

Why Custom Home for Your ADU Project

Custom Home Design and Build manages the entire ADU process from initial design through permit approval and construction. Our team produces permit-ready documents that address code requirements across Bay Area jurisdictions, reducing the chance of plan check corrections.

As a design-build firm, we coordinate architects, engineers, energy consultants, and contractors under one roof. This means faster document preparation, consistent plan sets, and a construction team that is already familiar with your project when permits are issued.

We have completed ADU projects across Santa Clara County, San Mateo County, and Alameda County. That experience gives us insight into each city’s review process, common plan check issues, and the best strategies for efficient permitting.

Start Your Fall ADU Strategy Now

The fall permit strategy works best when the design phase starts in summer. If you are considering an ADU, beginning the conversation now gives you time to complete design, engineering, and documentation by September or October.

Contact Custom Home Design and Build to schedule a consultation about your ADU project. We will assess your property, discuss your goals, and create a timeline that gets your ADU permitted and under construction on the best possible schedule.