Unincorporated San Mateo County requires vacant lot maintenance under Ordinance Code Chapter 4.48 and PRC §4291 (defensible space). Grass/weeds must not exceed 6-12 inches; wildfire zone lots require 100-foot defensible space clearance.
Vacant lot owners in unincorporated San Mateo County must maintain properties under multiple overlapping requirements. Ordinance Code Chapter 4.48 prohibits accumulated weeds, brush, rubbish, and junk. Grass and weeds generally must not exceed 6-12 inches depending on zone (stricter in fire hazard areas). Public Resources Code §4291 requires 100-foot defensible space around structures in State Responsibility Areas (SRA) and Very High Fire Hazard Severity Zones (VHFHSZ), which cover much of the Coastside, Skyline, and Peninsula ridge areas. Weed abatement programs run by County Fire and CalFire annually — inspections begin in May, notices issued in June, County abatement in July-August if not completed. Debris and illegal dumping on vacant lots must be removed. Vacant structures must be secured against trespass (boarded windows/doors). Some parcels may require vacant property registration. Coastal zone vacant parcels cannot be cleared below baseline vegetation levels without Coastal Development Permit.
Weed abatement: County contractor mows/clears at owner cost ($300-$2,000+ per parcel plus 50% admin fee) charged to property taxes. Defensible space violations under PRC §4291: CalFire citations up to $1,500. Repeat violations: daily fines, misdemeanor possible. CCC violations for over-clearing: separate enforcement.
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