California unincorporated profile
Outside the boundaries of incorporated cities and towns, the San Mateo County government is the planning and permitting lead agency. That means county zoning, county building codes, and county environmental review apply directly — without a separate city layer. The county rules most likely to catch a project applicant off guard are listed below.
These San Mateo County rules apply directly to projects in unincorporated areas of the county, with no city-level overlay.
The county's recently consolidated Protected Tree Ordinance is not effective in the Coastal Zone — separate heritage tree provisions apply there instead, so the same removal that needs one kind of permit inland requires a different process at the coast.
Properties in the Residential Hillside zoning district are protected by a lower tree trunk-size threshold than the rest of the county — so hillside homeowners may face permit requirements for trees that wouldn't be protected on a flatland parcel.
Construction in unincorporated San Mateo ends in the early evening on weekdays, starts later on Saturdays, and is prohibited on Sundays and most holidays — among the more restrictive construction-hour schedules in the Bay Area.
The entire western coastside — including Montara, Moss Beach, El Granada, and Pescadero — requires a Coastal Development Permit for most new development, stacked on top of county building permits.
The first habitat conservation plan adopted in the country covers a specific area around San Bruno Mountain, protecting several rare butterfly and snake species — new development in or near that area may trigger mitigation requirements not apparent from standard county zoning.
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Screen an addressSource: Headlands Environmental — environmental site screening for California. Rules summarized from publicly available county codes and planning documents; project review counts indexed from the State Clearinghouse. For authoritative requirements, consult San Mateo County directly.