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

Table 13-32, the Residential Development Standards table applicable to the R1, R2-MD, R2-HD, and R3 zones, sets 'Minimum Open Space' at 40% of total lot area for every residential zone in the city, meaning at least two-fifths of any residential lot must remain unbuilt. The table separately regulates rear yard coverage for lots whose rear does not abut a publicly dedicated alley, street, or park: main buildings are limited to 25% of the rear yard area, and accessory buildings such as garages or workshops to 50% of the rear yard area.

The code defines 'rear yard area' precisely as the lot width, measured from side property line to side property line, multiplied by 20 feet, so the coverage percentages apply to that fixed 20-foot-deep strip rather than the whole backyard. Where the rear yard instead abuts a publicly dedicated alley, street, or park, the rear yard coverage standard does not apply at all, and a five-foot rear setback controls instead, though garages may need extra depth for backup clearance. These standards work alongside the distance-between-buildings requirement of 10 feet between main buildings and 6 feet between main buildings and accessory structures, and property owners should check both the open space and rear coverage figures before finalizing addition or accessory-structure plans, since the reduced 10-foot single-story rear setback allowance elsewhere in the table depends on staying within the coverage limits.