Ontario, CA Building Setbacks & Zoning: Lot Coverage Limits (2026)

Ontario Municipal Code Chapter 9 (Zoning) sets maximum lot coverage for single-family zones at roughly 40 percent for larger lots (R-1-8,000) and up to 50 percent for smaller lots, counting principal dwelling plus detached accessory buildings. Coverage is measured by the footprint of all roofed structures. Impervious surface, including driveways and patios, is separately regulated under the Santa Ana Regional Municipal Separate Storm Sewer (MS4) permit which Ontario is a co-permittee of; projects creating or replacing 5,000 square feet of impervious area must provide on-site stormwater capture per the 2010 MS4 permit. Additions that push total coverage above the district maximum require a setback variance from the Planning Commission. Pervious pavers, decomposed granite, and artificial turf may be credited as partial impervious reduction. ADUs under 800 square feet are excluded from lot coverage calculations under AB 68 and Government Code 65852.2. Violations are identified during plan review and may trigger stop-work orders.