The percentage of a lot covered by buildings (main house + ADU + other structures) — typically capped by zoning.
Most California single-family zones cap lot coverage at 35-50%. Adding an ADU to an already-large house can push coverage over the limit. State ADU law allows some flexibility, but always verify with your city before designing.
Part of the BackyardADU California ADU Glossary — plain-English definitions of the regulatory, construction, and financing terms you'll encounter during a California ADU project.