Fairfield, CA Accessory Structures: ADU Rules (2026)

2. A detached ADU can't exceed 1,200 square feet, and an attached ADU is capped at 50 percent of the primary dwelling's floor area or 1,200 square feet, whichever is less. Height is limited to 16 feet to the roof peak, rising to 25 feet if more than half the ADU's floor area sits above an existing or proposed garage. Setbacks are four feet from side and rear lot lines for new construction, with no setback required when an ADU converts an existing structure in place, and a detached ADU must sit at least five feet from the primary dwelling.

Where standard zoning-district rules on lot coverage, floor area ratio, or setbacks would block an 800-square-foot ADU built 16 feet tall with four-foot side and rear setbacks, the code requires those regulations to be waived to permit that unit. No additional off-street parking is required for an ADU or JADU, and neither counts against the lot's permitted residential density. 2(e)(1) skip the Planning ADU Permit and go straight to a building permit application.