Cupertino, CA Accessory Structures: ADU Impact Fees (2026)
Key Facts
- Fee-exempt ADU size
- Under 750 sq ft: no impact fees
- Fee above threshold
- Proportional to primary dwelling size
- Governing citation
- CMC § 19.112.020
- State formula incorporated
- Gov. Code § 6324(c)(1)-(2) as cited
Summary
Cupertino cannot charge impact fees on an accessory dwelling unit or junior ADU under 750 square feet. Larger ADUs pay impact fees only in proportion to the primary dwelling's square footage, under Municipal Code Section 19.112.020, which writes the state ADU impact-fee formula directly into city law.
No impact fees, as defined in Government Code Section 6324(c)(2), shall be imposed on any accessory dwelling unit or junior accessory dwelling unit with a gross floor area of less than 750 square feet. Impact fees imposed on accessory dwelling units greater than or equal to 750 feet shall be charged proportionally in relation to the square footage of the primary dwelling unit in compliance with Government Code Section 6324(c)(1).
Full Breakdown
112, Cupertino's accessory dwelling unit ordinance, folds the fee limits set by state ADU law directly into the Municipal Code so builders do not have to separately track a state formula. 020 states that no impact fee, as defined by reference to Government Code Section 6324(c)(2), attaches to an ADU or junior ADU with a gross floor area under 750 square feet. 030A top out at 800 square feet for new construction and many conversions and detached units come in well under 750 feet. 020, rather than a flat per-unit rate.
112 that requires ADUs to meet the underlying zone's site development standards, and applies City-wide to every residential and mixed-use residential zoning district where ADUs are allowed. The Department of Community Development administers ADU building permits and calculates any applicable proportional fee at permit issuance, using the primary dwelling's recorded square footage as the base figure for the proration.
Violations & Fines
There is no separate penalty section for the fee cap itself; an applicant wrongly charged a fee can raise Section 19.112.020 during plan check or appeal the fee determination through the City's standard building permit appeal process. Charging a fee inconsistent with the 750-square-foot threshold exposes the City, not the applicant, to a challenge under state law.
Frequently Asked Questions
Do I pay impact fees on a small Cupertino ADU?
What happens once my ADU passes 750 square feet?
Which department calculates the ADU fee?
Sources & Official References
Other rules in Cupertino
California rules heatmap·Compare Cupertino to another location·View the California accessory structures overview
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ADU Impact Fees in Nearby Cities
How other cities in Santa Clara County handle adu impact fees.