San Mateo County, California Building Permit Guide

San Mateo County runs down the Peninsula from San Francisco to Silicon Valley, with about 744,000 residents, a coastline and the San Andreas fault. The Planning and Building Department is the authority for the unincorporated areas — the coastside, the hills and the bayside pockets — outside its 20 cities.

This guide covers the Planning and Building Department’s unincorporated-area role, Title 24 with county amendments, and the coastal-zone and seismic layers, and where city work goes instead.

This guide covers unincorporated San Mateo County. The county’s 20 cities each run their own permitting.

What requires a building permit in San Mateo County?

Local amendments and thresholds differ from one jurisdiction to the next, so an exempt list from a neighbouring city is not reliable — a project waved through in one place needs a full permit set in the next. An exemption from a building permit is never an exemption from zoning, the statewide energy or green-building codes, or an electrical or plumbing permit. Confirm scope with Planning and Building before work starts.

The statewide layers that apply everywhere

Several parts of Title 24 apply on top of the base building code and routinely catch projects owners assume are exempt: the California Energy Code (Part 6); CALGreen (Part 11), California’s mandatory statewide green-building code; and the accessibility provisions in Chapters 11A and 11B. Seismic design is built into the code statewide, and in fire-prone areas the California Wildland-Urban Interface Code (Title 24, Part 7, in force since 1 January 2026) and Cal Fire defensible-space requirements (Public Resources Code 4291) add a further layer. In unincorporated San Mateo County, the Planning and Building Department administers Title 24 with county amendments, and coastal-development and seismic review attach to many coastside and hillside parcels.

California builds on one statewide code, Title 24, whose 2025 edition took effect on 1 January 2026; the editions in effect when the application is submitted apply, and cities and counties may adopt local amendments only with findings filed with the state (new residential amendments are largely frozen until June 2031). Title 24 and local amendments

Who handles permitting in San Mateo County?

The Planning and Building Department handles permitting and inspections for unincorporated San Mateo County; the 20 cities handle their own.

The Planning and Building Department is the authority for unincorporated San Mateo County, working from its Redwood City office and online systems. Coastside parcels add coastal-development review, and hillside and fault-corridor parcels turn on seismic and grading design.

Confirm the jurisdiction from the parcel first; a project inside a San Mateo County city files with that city’s department under its own code and counter.

In 2025, building permits issued in unincorporated San Mateo County authorized 183 new privately owned housing units, 53 of them single-family homes, according to the U.S. Census Bureau Building Permits Survey.

Permit types

Residential permits

Unincorporated residential work is permitted and inspected by the county under Title 24 and county amendments. Additions, decks, pools, solar and EV chargers need permits, coastside parcels carry added review, and hillside parcels carry grading and seismic design. A CSLB-licensed contractor pulls the trade permits.

Commercial permits

Commercial and multi-family work in unincorporated areas goes through county plan check against the California Building Code, the Energy Code and CALGreen. It requires CSLB-licensed contractors, stamped drawings with seismic design, and coastal-development review where the parcel sits in the coastal zone.

Licenses, trade classifications and design professionals

Practically, three credential layers appear on California projects: a CSLB license in the correct classification for the contractor pulling the permit; the specialty C-classifications for the electrical, plumbing and mechanical trades; and, on commercial and larger residential work, drawings stamped by a California-licensed architect or engineer. Confirm what Planning and Building requires for the specific building before filing.

Contractors are licensed statewide by the Contractors State License Board (Classes A, B, B-2 and C) for work of $1,000 or more or any permitted work; a city may also require a business licence or tax registration. Contractor licensing in California

San Mateo County permit costs and fees

Budget the county building permit and plan-check fees, separate trade permits, the state Building Standards and seismic surcharges, and coastal or hillside review where it applies. The county publishes a valuation-based schedule; confirm it for your filing date.

California layers two uniform state surcharges — the Building Standards Administration fee and the Strong Motion Instrumentation seismic fee — on top of the local charges (Health and Safety Code 18931.6; Public Resources Code 2705). The building and plan-check fees themselves are local and change, and California law limits them to the reasonable cost of providing the service, so a figure from a neighbouring city is not reliable — ask Planning and Building for the schedule in force on your filing date.

Trade permits and who may pull them

Each trade follows its part of Title 24 and is done by a contractor with the matching CSLB licence (C-10 electrical, C-36 plumbing, C-20 HVAC), a Class B contractor where allowed, or an owner-builder. Trade licences in California

How to apply for a San Mateo County building permit

Review, corrections and what actually causes delay

In California, the first cause of delay is uncertainty over jurisdiction — filing with the county when a city should have it, or missing a local amendment on top of Title 24. After that come Title 24 energy and CALGreen documentation, a CSLB classification that does not match the scope, and, in fire or coastal areas, defensible-space or coastal-zone requirements that were not addressed up front. Build the plan-check time into the schedule and confirm the checklist with Planning and Building before filing.

A building permit carries a validity period and can expire if work does not start or stalls between inspections; confirm the expiry with San Mateo County on phased or delayed work. Permit validity in California

Inspections in San Mateo County

Where a permit is required, standard checkpoints include footing and foundation, framing, rough-in electrical, plumbing and mechanical, insulation and Title 24 energy, CALGreen measures, fire systems on commercial work, and final, with a certificate of occupancy before use. On issuance the county assigns the field inspector and the construction stages that must be inspected.

California inspections are made against the code editions in effect when the permit application was submitted (Health and Safety Code 18938.5), so the approved plans and any energy and green-building documentation need to be on site for the inspector to check against. Confirm the notice Planning and Building needs and schedule around its inspection windows.

Do not cover work before the required inspection has been approved. Keep the issued permit, the approved plans, product listings, Title 24 energy documentation and your correction responses available on site.

San Mateo County permit search and official resources

Permit records in California sit with the local authority that issued them. Where the County of San Mateo Planning and Building Department is the authority for unincorporated San Mateo County, it holds the building permit, the inspection history and the certificate of occupancy. If you are buying, refinancing or renovating, confirm that past work was permitted rather than assuming it was — and confirm the code edition that was in force.

These are the primary sources behind this guide. Codes, fee schedules and procedures change — confirm the position for your filing date.

• County of San Mateo Planning and Building
• California Building Standards Commission (Title 24)
• Contractors State License Board (CSLB)
• California Coastal Commission
• California Department of Housing and Community Development

Frequently asked questions

Who issues building permits in unincorporated San Mateo County?

The Planning and Building Department issues permits for unincorporated areas such as the coastside and hills; the county’s 20 cities run their own departments.

Does my project need coastal review?

Coastside parcels commonly do; a coastal-development permit can be required on top of the building permit, so confirm before you file.

How does seismic design affect my project?

Seismic design is central along the San Andreas corridor; expect it to shape foundations, framing and connections on most projects.

Do I need a local contractor registration?

Not a contractor licence: California licenses contractors statewide through the CSLB, and the licence must be active and carry the right classification. A city may still require a business licence or business tax registration (Government Code 37101), so ask the department.

How do I know if my parcel is unincorporated?

Confirm with the Planning and Building Department or the county mapping tools; coastside and hill parcels outside the cities file with the county.

How do I run a San Mateo County permit search?

The Planning and Building Department holds unincorporated permit and inspection records; city records sit with each city’s department.

Simplify San Mateo County permitting with Alliance Permitting

Unincorporated San Mateo County turns on jurisdiction, coastal review and seismic design. Clearing those before filing is most of the battle from the coastside to the fault corridor.

Trusted by leading builders, developers, and national contractors — 21+ years of filing in the jurisdictions we write about.

Contractors and builders choose Alliance for San Mateo County because the work is done by people who have stood at the counter:

• We confirm whether the parcel is unincorporated or inside a city.
• We manage the county application end to end.
• We confirm the CSLB classification matches the scope.
• We clear coastal-zone and seismic review before filing.
• We submit complete plan sets and track issuance and inspections.

Alliance Permitting is a permit documentation and submission company in California. We prepare your paperwork, file it correctly and coordinate with the permitting authority through issuance. We are not a contractor and we do not perform licensed plan review or inspections; that work stays with your licensed team and the jurisdiction.

This guide is provided by Alliance Permitting for general information about San Mateo County permitting. Requirements, fees, and procedures change; confirm details with the permitting authority before relying on them.