Hercules, CA Accessory Structures: ADU Rules (2026)

320 implements state ADU law locally and lets the Community Development Director approve ADU building permits ministerially, with no hearing, acting within 60 days of a complete application for a lot with an existing home. Attached and detached ADUs are capped at 850 square feet for a 1-bedroom unit and 1,000 square feet for more than 1 bedroom, while a Junior ADU built inside an existing single-family home tops out at 500 square feet. Setbacks are minimal: no setback at all is required for an ADU built within existing space (garage conversions, for example) as long as side and rear clearances remain fire-safe, and every other ADU needs just 4 feet from side and rear lot lines, with front and corner setbacks matching the primary residence.

Height is capped at 16 feet for a new detached ADU, rising to 18 feet within a half-mile of a high-quality transit corridor or major transit stop, or if the ADU sits on a lot with an existing or proposed multifamily building; 2 additional feet of roof height are allowed to match the primary dwelling's roof pitch. 5 mile of transit, in historic districts, converted from existing structures, or within 1 block of a car-share location. 5 must bar rentals under 30 days and separate sale from the primary home before the City will issue the building permit, and a statewide-exemption pathway allows a detached, new-construction ADU up to 800 square feet with only 4-foot side/rear setbacks and building-permit-only review, no discretionary permit at all.