Petaluma, CA Accessory Structures: Shed Rules (2026)

Sonoma County's rules for detached residential accessory structures - sheds, gazebos, pool houses, workshops, detached garages, greenhouses, playhouses, carports, and similar - are administered through Permit Sonoma's Administrative Policy 1-4-6 (Detached Residential Accessory Structures), Sec. 26-88-040 of the Zoning Code (Accessory Buildings and Uses), and Chapter 7 (Building Regulations) of the County Code which adopts the California Building Code, Residential Code, and Fire Code. California Building Code Sec. R105.2 (as adopted by Chapter 7) exempts one-story detached accessory structures used as tool or storage sheds, playhouses, or similar uses from building-permit requirements if (a) the floor area does not exceed 120 square feet and (b) the height above grade does not exceed 12 feet. Under Permit Sonoma 1-4-6, only one permit-exempt structure is allowed per parcel unless additional structures are separated by more than 50 feet from any other permit-exempt structure. The exemption applies only to building permits - the structure still must comply with zoning setbacks, height limits, floor-area-ratio limits, and any combining-district requirements. Structures exceeding 120 square feet, exceeding 12 feet in height, or providing electrical, plumbing, or mechanical service require a building permit; permit-required structures may not exceed 15 feet in height (measured to ridge or top of parapet) under Sec. 26-88-040 unless the underlying zone allows greater height. Front-yard and street-side setbacks (typically 20-30 feet for residential zones, more for AR/RR rural residential) prohibit any detached accessory structure; side and rear setbacks (typically 5-15 feet depending on zone) apply but Sec. 26-88-040 allows a detached accessory structure to be placed within 3 feet of a side or rear lot line in some districts if certain fire-resistive construction requirements (California Residential Code Sec. R302.1 - one-hour fire-resistive walls within 5 feet of property line, no openings within 3 feet) are met. Total coverage of detached accessory structures in the rear yard may not exceed 50% under Sec. 26-88-040. Designated creek setback areas (typically 50-100 feet from top-of-bank along blue-line streams, per Sec. 26-66 Riparian Corridor combining district) prohibit accessory structures. Sheds in CAL FIRE State Responsibility Areas or Very High Fire Hazard Severity Zones - which cover much of unincorporated Sonoma County including the Mayacamas, Sonoma Mountain, Russian River, and Mark West Springs areas burned by the 2017 Tubbs Fire, 2019 Kincade Fire, and 2020 Glass Fire - must comply with Public Resources Code Sec. 4291 defensible space (30-foot 'lean, clean, and green' zone and 30-100 foot 'reduced fuels' zone, even around outbuildings), and sheds permitted as new construction must meet California Building Code Chapter 7A ignition-resistant standards if larger than the 120-sq-ft permit exemption. Scenic Resources (SR), Visitor Open Highway (VOH), Coastal (CC), and Floodway (FW) combining districts impose additional siting, color, materials, and elevation requirements. Sheds used for storage of fertilizers, pesticides, fuels, or other hazardous materials may trigger Sonoma County Department of Health Services or Hazardous Materials Office permit requirements under Sonoma County Code Chapter 30. Sheds containing plumbing or electrical service that could be converted to habitable space may be deemed a 'second dwelling' and subject to Sec. 26-88-060 ADU regulations or violation notices.