ADU rules in Vacaville, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Vacaville permits ADUs and JADUs ministerially under VMC 14.09.122 in conformance with California Government Code 66310 et seq. (renumbered from 65852.2 effective 2024). ADU maximum size scales with the primary dwelling: 850 sq ft if primary is up to 1,700 sq ft, 1,000 sq ft if primary is up to 2,000 sq ft, and 1,200 sq ft (or 50% of primary if larger) otherwise. ADUs cannot be used for short-term rentals under 31 days.
California's ADU statute was renumbered to Government Code 66310-66339 in 2024 (formerly Gov. Code 65852.2). Vacaville's implementing standards live at VMC 14.09.122, with cross-reference in VMC 14.09.270 (Standards For Specific Uses and Activities). Review is ministerial - no public hearing, no Planning Commission action, no discretionary design review (Gov. Code 66317). Size scaling under VMC 14.09.122: primary dwelling up to 1,700 sq ft permits an ADU up to 850 sq ft; primary up to 2,000 sq ft permits an ADU up to 1,000 sq ft; primary up to 2,400 sq ft permits 1,200 sq ft; primary over 2,400 sq ft permits up to 50% of primary dwelling size as the ADU. State law overrides on minimum-floor-area maximums (Gov. Code 66323) ensure at least 800 sq ft is allowed regardless of local caps. JADU maximum is 500 sq ft inside the primary dwelling per Gov. Code 66333. Vacaville eliminated lot coverage, setback, and architectural requirements specifically for ADUs (matching Gov. Code 66323) - the state default 4-foot side and rear setbacks apply. Owner-occupancy is required only for ADUs permitted after January 1, 2025 (under Gov. Code 66332(a), reinstated by SB 477 in 2024), and for JADUs (Gov. Code 66333). Short-term rentals under 31 days are expressly prohibited per VMC 14.09.122 and the recorded ADU covenant. The Vacaville Planning Commission recommended a 2025 ordinance amendment to conform to AB 462, AB 1154, SB 9, and SB 543. Garage-conversion ADUs are explicitly permitted under Gov. Code 66320(a)(1).
Constructing an ADU without permits violates VMC 14.09.122 and VMC Title 15. Vacaville Code Enforcement can issue stop-work orders, double permit fees on after-the-fact applications, and orders to expose concealed work. Operating an ADU as a short-term rental violates VMC 14.09.122 and is enforced through citations starting at $100 escalating to $500+ per VMC Title 8 Chapter 8.10. The state-mandated 60-day permit action window under Gov. Code 66317 means a complete application not acted on within 60 days is deemed approved.
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