Sunnyvale, CA Accessory Structures: ADU Impact Fees (2026)

California state law - Government Code 65852.2(f)(3) - prohibits Sunnyvale from charging any impact fees on an ADU under 750 sq ft. This exempts the unit from Sunnyvale Park Dedication and Park In-Lieu fees (SMC Title 18), traffic and capital facilities impact fees, school impact fees from Sunnyvale School District and Fremont Union High School District (currently around $5.17/sq ft of residential under Education Code 17620), and most sewer/water capacity charges from Sunnyvale's Water and Sewer Utilities. For ADUs 750 sq ft or larger, impact fees are charged proportionally based on the ratio of ADU floor area to primary dwelling area under Gov. Code 65852.2(f)(3)(B). Sunnyvale's regular building permit and plan-check fees apply at any ADU size and typically run $3,000-$6,000 - moderate by Silicon Valley standards (Cupertino, Palo Alto, Mountain View are higher). Sunnyvale's adopted Building Code is in SMC Title 16. The city does not have a separate Affordable Housing Mitigation Fee specifically on residential ADUs, and the Below Market Rate (BMR) requirements in SMC Chapter 19.66 apply only to projects of 5+ units, so individual ADUs do not trigger BMR obligations. The Mitigation Fee Act (Gov. Code 66020) governs all fee assessments and the protest process.