Budget about $12,000 in permits and fees for an 800 square foot detached ADU nationally, or $22,000 in California, per the ADU Wizard cost engine (estimate). The city's own building fees are often much less: $0 in Los Altos, $3,323 to $5,151 in San Jose. In California, impact fees only start above 750 sq ft.
Last verified: October 19, 2026
"What does the permit cost" is really four or five questions bundled together. There is the building permit and plan check the city charges to review your plans, sometimes a planning fee, then impact fees that only kick in above certain sizes, and utility fees that come from a separate agency entirely. I have seen homeowners budget for the first and get blindsided by the last.
ADU Permit Cost by Type
This is the permits-and-fees line from our cost engine, the allowance I would put in a budget before I know the city. It covers the whole permit bill, so it runs higher than any one city's building fee.
| Type | Size | Permits and fees, national (estimate) | Permits and fees, California (estimate) |
|---|---|---|---|
| Junior ADU | 400 sq ft | $1k to $2k | $2k to $4k |
| Garage conversion | 400 sq ft | $1k to $2k | $2k to $3k |
| Attached ADU | 600 sq ft | $5k to $9k | $10k to $16k |
| Detached ADU | 800 sq ft | $9k to $15k | $16k to $27k |
Source: ADU Wizard cost engine, the "Permits and fees" line of each type's breakdown at standard finish. A planning allowance, not a city fee schedule.
The Fees That Make Up an ADU Permit
| Fee | Who charges it | How it is set | Example we have cited |
|---|---|---|---|
| Building permit | City building division | By valuation or by ADU size | San Jose: $3,323 up to 750 sq ft, $5,151 for 751 to 1,200 sq ft; Campbell: 2.00% of the first $500,000 of valuation |
| Plan check | City building division | Usually a share of the building permit fee | Sunnyvale: 70% of the permit fee; Campbell: 33% |
| Planning fee | City planning division | Flat, and only on some paths | Sunnyvale: $268 for new ADUs over 800 sq ft; Santa Clara: $306.00 |
| Impact fees | City | None at 750 sq ft or less in California; proportionate above | Sunnyvale's Transportation Impact Fee applies over 750 sq ft |
| School fees | School district | Per square foot, above a size line | Sunnyvale applies it from 500 sq ft of new living area; San Jose says none under 750 sq ft |
| Park fees | City | Flat or per unit, above a size line | Campbell: $9,328 at 750 sq ft or larger; Los Angeles: $0 at any size |
| Water and sewer connection | Utility or sanitation district | Capacity charges, often by fixture count | Sunnyvale exempts ADUs from incremental connection fees; Los Gatos's West Valley Sanitation District caps its detached ADU buy-in at $6,800 |
Sources: each city's figures as cited on its ADU Wizard permit guide; the California 750 sq ft rule is Government Code 66311.5(c)(1), as covered on our California ADU permit guide.
The 750 Square Foot Impact Fee Line (California)
This is the single most useful number for a California budget. Under Government Code 66311.5(c)(1), a city cannot charge impact fees on an ADU of 750 square feet or less of interior livable space, or on any junior ADU. Above 750, impact fees have to be proportionate to the ADU's size compared with the main house. Since January 1, 2026, that 750 is measured as interior livable space (SB 543), not gross floor area.
The line softens on January 1, 2027. Under SB 1117 (Chapter 809, Statutes of 2026), for up to two ADUs on a lot, impact fees on an ADU over 750 square feet are charged only on the interior livable space above 750, still in proportion to the main house. An 800 square foot ADU is then charged on 50 square feet, not 800. The bill does not say whether your application date or the fee assessment date decides which rule applies, so ask your city. SB 1117 does not touch permit, plan check or utility connection fees.
Here is the catch. "Impact fees" are not all fees. Building permit and plan check are service fees, so they still apply at any size, and school districts set their own lines. And cities word their thresholds slightly differently: Sunnyvale's traffic fee applies "over 750," Campbell's park fee "at 750 or larger." If your design sits right at the line, ask the city which side you are on before you finalize the floor plan. Our California ADU size limits page explains how interior livable space is measured.
ADU Permit Fees by City
Only fee lines our permit guides cite to the city's own fee schedule or fee page. Where a city publishes only a calculator or a valuation formula, I would rather link you to the guide than quote a number I cannot source.
| City | Fee | Amount | City source |
|---|---|---|---|
| Los Altos ADU permit guide | ADU building permit, plan check and MEP permit | $0.00 | FY2025-2026 Development Services fee schedule |
| Los Altos ADU permit guide | Construction tax (LAMC Chapter 3.24) | $0.42 per sq ft | FY2025-2026 Development Services fee schedule |
| San Jose ADU permit guide | Building Division fee, 0 to 750 sq ft | $3,323 | FY 2024-25 Building Division Fee Schedule (latest we could confirm) |
| San Jose ADU permit guide | Building Division fee, 751 to 1,200 sq ft | $5,151 | FY 2024-25 Building Division Fee Schedule (latest we could confirm) |
| Sunnyvale ADU permit guide | Plan check | 70% of the building permit fee | FY 2026-27 Master Fee Schedule |
| Sunnyvale ADU permit guide | Planning Miscellaneous Plan Permit (new ADUs over 800 sq ft) | $268 | FY 2026-27 Master Fee Schedule |
| Campbell ADU permit guide | Building permit fee | 2.00% of first $500,000 of valuation | FY2026-27 Master Fee Schedule |
| Campbell ADU permit guide | Plan check | 33% of building permit fee | FY2026-27 Master Fee Schedule |
| Campbell ADU permit guide | Park in-lieu fee | $0 under 750 sq ft, $9,328 at 750 sq ft or larger | FY2026-27 Master Fee Schedule |
| Santa Clara ADU permit guide | Architectural Review / ADU fee | $306.00 flat | Planning Application Fee Schedule, effective July 1, 2026 |
| Berkeley ADU permit guide | Neighbor notification fee | $500 | City of Berkeley |
| Berkeley ADU permit guide | Address assignment fee | $250 | City of Berkeley |
| Long Beach ADU permit guide | Processing fee | $115 flat | City of Long Beach fee schedule page |
| Long Beach ADU permit guide | Technology and General Plan surcharges | 6% of applicable fees | City of Long Beach fee schedule page |
| Los Angeles ADU permit guide | Park fee (LAMC 12.33) and Affordable Housing Linkage Fee | $0, any size | LADBS and LAMC, per our Los Angeles permit page |
| Los Gatos ADU permit guide | Use and occupancy clearance (new secondary dwelling unit) | $0 | Town fee schedule effective July 1, 2026 |
Source: each linked ADU Wizard permit guide and the city fee document it cites. Fee schedules change every July in most California cities; confirm before you budget.
Our other permit guides cover cities that do not publish a flat ADU fee we can quote, usually because the fee is valuation-based or estimated through a calculator: Cupertino ADU permits, Portland ADU permits, Riverside ADU permits, Saratoga ADU permits. For the statewide rules, see the California ADU permit guide and the Oregon ADU permit guide.
How to Keep Permit Fees Down
- Stay at or under 750 square feet in California if the extra space is not worth the impact fees. From 2027 the penalty for going over is smaller, because only the space above 750 is charged.
- Use a pre-approved plan. Berkeley cuts plan check 50% for its pre-approved designs, and Santa Clara charges 25% of the original review fee for listed plans.
- Convert instead of building new. A conversion or JADU avoids most site and utility work; Sunnyvale and many districts exempt them from connection fees.
- Submit a complete set. Sunnyvale bills resubmittal plan check at $265 an hour, so every correction round costs money, not just time.
Fees are usually the smallest part of the budget, which is exactly why they get ignored until the invoice arrives. For the full build, our California ADU cost guide and the Data Hub carry the rest, and our guide to how long it takes to build an ADU covers the permit timeline in every city we track.
Frequently Asked Questions
How much does an ADU permit cost?
It depends almost entirely on your city. Among the cities whose fee schedules we have cited, building permit and plan check fees run from $0 in Los Altos to $3,323 or $5,151 in San Jose depending on size. For a full permit allowance including impact and utility fees, our cost engine budgets about $12,000 for an 800 square foot detached ADU nationally and $22,000 in California (estimate).
Are ADU impact fees waived in California?
Yes, for an ADU of 750 square feet or less of interior livable space and for any JADU, under Government Code 66311.5(c)(1). Above that, a city can charge impact fees proportionate to the ADU size compared with the main home. Building permit and plan check fees are not impact fees, so they still apply.
What fees are included in an ADU permit?
Usually a building permit fee and a plan check fee, often set by valuation or by size, plus small surcharges (technology, general plan). Some cities add a planning fee. Above the size thresholds, school, park and traffic impact fees can apply, and water and sewer agencies may charge connection or capacity fees.
Do ADUs pay school fees?
Often only above a size line, and the school district sets it, not the city. San Jose's fees page says none applies under 750 square feet, while Sunnyvale's ADU brochure applies its school fee to new construction with 500 square feet or more of living area. Check with your district.
What is the cheapest city for an ADU permit?
Of the cities we track, Los Altos, which lists its ADU building permit, plan check and MEP permit at $0.00 in its FY2025-2026 fee schedule. Its construction tax of $0.42 per square foot and outside agency fees still apply.
If I were budgeting a California ADU tomorrow, I would start from the engine's permit allowance above, then replace it line by line with my city's published schedule once I had a design. The ADU permits hub is where every city guide lives.