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

San Bernardino County Development Code regulates both building lot coverage and impervious surface coverage on parcels. Single-family residential zones typically allow 40 to 50 percent building coverage, with higher-density multi-family zones permitting up to 60 percent. Rural Living zones limit coverage to 20 to 30 percent to preserve open character. Lot coverage is calculated as the sum of all structures and roof overhangs over 30 inches divided by total parcel area. Driveways, patios, and decks under 30 inches in height are typically excluded from building coverage but count toward impervious surface limits. Impervious surface limits of 50 to 70 percent apply in watershed protection overlay zones and areas draining to creeks or reservoirs. Hillside development overlay zones further restrict coverage based on slope, with steeper slopes reducing allowable footprint to preserve natural drainage and vegetation. Accessory structures and ADUs count toward coverage, though state ADU law exempts certain conversion ADUs from local coverage limits. Swimming pools, pool decks, and detached garages all contribute to calculations. Stormwater management requirements under County MS4 permit may require on-site infiltration when coverage exceeds thresholds.