The ADU Permit Process, Step by Step (2026)

Permitting is the part of an ADU project people fear most, and the fear is mostly outdated. In California, state law now requires cities to approve code-compliant ADUs ministerially — no public hearings, no neighbor objections, no discretionary review — within 60 days of a complete application. The process is paperwork, not politics. Here's what actually happens, stage by stage.

Stage 1: Feasibility (before you spend real money)

Start with your city's ADU page and confirm the basics for your lot: maximum unit size, setback requirements (typically 4 feet side and rear), height limits, and whether anything unusual applies — coastal zones, historic districts, fire-hazard zones, and hillside overlays can each add requirements or entire extra permits. This is an afternoon of reading that prevents months of redesign. Our city guides summarize these rules for major markets, including the exceptions.

Stage 2: Design and plans

You'll need professionally drawn plans: site plan, floor plans, elevations, structural details, and energy compliance documentation. Three routes, in ascending cost: your city's pre-approved plan program if it has one (Los Angeles has 80+ standard plans; San José issues same-day permits for qualifying pre-approved designs; Sacramento and Oakland run programs too — this route can save $5,000–$15,000 and months), a prefab ADU company whose plans have been permitted before, or custom design from an architect or designer. Custom typically runs 8–15% of construction cost and only earns its keep on difficult lots or specific needs.

Stage 3: Plan check and corrections

You submit plans, the city reviews them against building code, and — this is the part nobody warns you about — they almost always come back with corrections. This is normal, not failure. One or two correction cycles is standard even for professional plans. Each cycle takes weeks, which is why "60-day approval" and "getting your permit" aren't the same date: the 60-day clock applies per complete review round. Realistic total permitting time runs from same-day (pre-approved plans in San José) to roughly 2–6 months for custom plans, with San Francisco's median stretching toward 186 days.

Stage 4: Permit issuance and fees

When plans clear, you pay the fees and receive the permit. Budget realistically: in California's major cities, permits and city fees run roughly $3,500–$30,000 depending on the city and unit size. The single biggest lever is size — units under 750 sq ft are exempt from development impact fees statewide, which in high-fee cities saves $15,000–$25,000. If your unit is hovering just over 750 sq ft, this is the moment to reconsider.

Stage 5: Construction inspections and final

Your permit comes with a schedule of inspections — foundation, framing, rough electrical and plumbing, insulation, final. Your contractor calls for each as work progresses; failed inspections mean fixing and re-inspecting, which is friction but rarely crisis. The finish line is the final inspection and certificate of occupancy: the document that makes your ADU legally habitable and rentable. Don't let anyone move in before it — an unpermitted occupancy can unwind insurance, financing, and future sale.

The pattern across all five stages: cities reward preparation. A complete application with pre-approved or professionally prepared plans moves through a fundamentally different (and faster) pipeline than an improvised one. Slow down at stages 1 and 2, and stages 3 through 5 speed up.

Run the numbers for your project

Every project is different — size, scope, and city move the total by six figures. Get an itemized estimate in under a minute:

Written and reviewed by ADUCostGuide. Cost figures reflect 2026 data and typical projects; rules and prices vary by city — see our city guides and confirm details with your local planning department and licensed contractors.