Can I Build an ADU in Vacaville?

Yes — by right

ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.

1 ADU + 1 JADU

At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).

Conversion ADUs (≥1, up to 25% of units) + up to 8 detached

Conversions of non-livable space (at least 1, or up to 25% of existing units) plus up to 8 detached ADUs on a lot with existing multifamily — never exceeding the number of existing units. JADUs are single-family only.

Allowed

Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).

1,200 sq ft

Statewide default cap for detached new-construction ADUs in the absence of a compliant local ADU ordinance. The unconditional by-right floor a city must always allow is 800 sq ft (see Guaranteed minimum size); a city with a compliant ordinance may set its own ceiling.

Detached ADU up to 1,200 sq ft. Attached ADU: 850 sq ft if the primary dwelling is ≤1,700 sq ft (≤1 bedroom), 1,000 sq ft if the primary is ≤2,000 sq ft (2+ bedrooms), otherwise 50% of the primary dwelling or 1,200 sq ft, whichever is less

Vacaville sets explicit attached-ADU size tiers keyed to the primary dwelling's living area. Minimum living area is 190 sq ft. State minimums (≥850, ≥1,000 for 2+ bedrooms) are preserved.

800 sq ft

Vacaville's stated minimum LIVING area for an ADU is 190 sq ft; the 800 sq ft figure here is the state-protected by-right floor a city cannot zone below, not a Vacaville-specific number.

500 sq ft

16 ft

16 ft base for a new detached ADU; 18 ft within ½ mi of a major transit stop/high-quality corridor (plus 2 ft, to 20 ft, for roof pitch aligned with the primary dwelling) and 18 ft on a lot with a multistory multifamily dwelling. Attached/expansion ADUs may reach 25 ft.

4 ft

A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.

4 ft

No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone

None required

No statewide separation requirement between the ADU and the primary dwelling.

Up to 1 space

At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.

Yes — no parking required near transit & for conversions

No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.

Not required

When a garage/carport is demolished or converted to build an ADU, replacement parking cannot be required.

Ministerial (by right)

No public hearing or discretionary design review for a qualifying ADU.

60 days

The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.

Only for a JADU

No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.

Waived under 750 sq ft

An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.

Building permit, Recorded owner-occupancy / use deed restriction

For ADU permits issued on/after Jan 1, 2025, Vacaville requires a recorded Solano County deed restriction and, by its terms, owner-occupancy of either unit (§ 14.09.270.040.F.1). The owner-occupancy mandate is preempted by Cal. Gov. Code § 66315 for ADUs and should be unenforceable; the deed restriction also bars separate sale and rentals under 31 days. Confirm current practice with Vacaville Community Development.