Napa County, CA Accessory Structures: Shed Rules (2026)

Napa County adopts the California Building Code with local amendments under Napa County Code Title 15 (Buildings and Construction). California Building Code Section 105.2 exempts one-story detached accessory structures used as tool and storage sheds, playhouses, and similar uses from the building permit requirement when the floor area does not exceed 120 square feet (Item 1). Napa County PBES applies that exemption to ordinary backyard sheds in residential and agricultural zones. The exemption is from the building permit only - it does not waive zoning compliance. Under Napa County Code Title 18 (Zoning), even an exempt shed must comply with the setback, lot coverage, and height standards of the underlying zoning district. In residential districts, sheds typically must observe the side and rear yard setbacks of the underlying zone (commonly 5 feet for one-story accessory structures, but check the specific zone), cannot encroach into the required front yard, and may not exceed accessory-structure height limits (typically 15 feet for a one-story shed). Sheds larger than 120 square feet, sheds with any electrical or plumbing work, sheds intended for human occupancy (which would be an ADU or JADU under Sec. 18.104.180), and any structure on slopes greater than the County's hillside thresholds require a building permit and may trigger grading review. Agricultural accessory structures used exclusively for agricultural purposes on agricultural land may qualify for the agricultural building exemption in California Health & Safety Code Section 17021 and California Building Code Section 105.2 (Item 3), which exempts them from many residential building code requirements when no humans live or work in them on a regular basis. Sheds in CAL FIRE State Responsibility Areas, Very High Fire Hazard Severity Zones, or designated Wildland-Urban Interface areas - which covers most of unincorporated Napa County - must comply with California Building Code Chapter 7A ignition-resistant construction standards if they exceed certain size thresholds or are located near a primary dwelling, and the structure and its surroundings must comply with Public Resources Code Section 4291 defensible space requirements. After the 2017 Atlas Fire, 2017 Tubbs Fire, 2020 LNU Lightning Complex, and 2020 Glass Fire, the County and CAL FIRE actively enforce hardening and defensible space standards on outbuildings.