Santa Clara County, CA Environmental Rules: Grading & Drainage (2026)

The county Grading Ordinance in Division C12 requires building sites to slope away from foundations at a minimum of 5 percent fall for the first 10 feet under CBC 1804.4 as amended. All drainage must be conveyed to an approved outlet such as a public storm drain, natural watercourse, or a percolation system meeting soil infiltration rates. Redirecting surface runoff onto adjoining private property is prohibited and actionable under common law nuisance and the California Rule of Reasonable Use codified in Keys v. Romley case law. New subdivisions and major remodels must prepare a site drainage plan stamped by a civil engineer when lot area exceeds 10000 square feet or slopes exceed 10 percent. Hillside lots frequently require subsurface drains, area drains, and energy dissipation at outlets to prevent erosion. French drains and dry wells must be sited at least 10 feet from any structure and 5 feet from property lines. Sump pumps may not discharge to the sanitary sewer per Santa Clara Valley Water District rules and must discharge to a storm outlet or approved infiltration system. Violations are enforced by County Code Enforcement and can include stop work orders, mandatory regrading, and administrative penalties. Civil disputes between neighbors over redirected drainage are heard in Superior Court and frequently result in injunctions requiring grading restoration.