San Mateo County, CA Property Maintenance: Vacant Lot Maintenance (2026)

San Mateo County does not appear to publish a distinct ordinance addressing vacant lots specifically; instead, the County applies its general public-nuisance and property-maintenance authority to all parcels in the unincorporated area, including undeveloped or vacant ones. The Planning and Building Department's Code Compliance Section addresses public nuisances created by a lack of property maintenance, and the County uses refuse accumulating in a yard as a textbook example of an abatable nuisance. Property-maintenance standards applied on the County's Notice of Violation forms (drawn from the International Property Maintenance Code) require removal of overgrown and dead weeds and vegetation, with growth kept at a maximum height of 18 inches or less, and require accessory structures, fences, and walls to be kept in good repair. For a vacant lot, the same abatement procedure applies: the Code Enforcement Unit issues a Notice and Order to Abate, the owner has 10 days to correct the condition, and if it is not corrected the County may abate it and bill the owner for actual costs plus a 15% administrative fee. Vegetation that constitutes a fire hazard is separately addressed by hazardous-vegetation abatement under California Health and Safety Code Section 14875 et seq. and the County's fire-prevention authority; the 18-inch property-maintenance standard is a code-compliance maintenance threshold rather than a wildfire defensible-space rule.