San Mateo County enforces 2025 CBC, T24 Pt 2 based on 2024 IBC with 2 local amendments on top. The amendments are the part that gets sets corrected. The state edition is only the floor.
Current edition
2025 Title 24
Prior edition
2022 Title 24
Code authority
San Mateo County Planning and Building Department
Edition changeover: Projects with a complete application on or before 2025-12-31 may still be reviewed under the 2022 Title 24.
Adopted code and local amendments by discipline
Adopted code editions and local amendments by discipline
Discipline
Adopted code
Local amendment
Building
2025 CBC, T24 Pt 2 based on 2024 IBC
San Mateo County Ord. No. 4916 (adopted 2026-03-10, LATE: state code governed 2026-01-01 onward), Title 10 repealed + re-adopted w/ 2025 CBSC Parts 1-12 + 2024 IPMC incl. local amendments
Residential
2025 CRC, T24 Pt 2.5 based on 2024 IRC
n/a
Existing buildings
2025 CEBC, T24 Pt 10 based on 2024 IEBC
n/a
Fire
2025 CFC, T24 Pt 9 based on 2024 IFC
n/a
Electrical
2025 CEC, T24 Pt 3 based on 2023 NEC
n/a
Mechanical
2025 CMC, T24 Pt 4 based on 2024 UMC
n/a
Plumbing
2025 CPC, T24 Pt 5 based on 2024 UPC
n/a
Energy
2025 Energy Code, T24 Pt 6
n/a
Green / sustainability
2025 CALGreen, T24 Pt 11
n/a
Accessibility
2025 CBC Ch 11A/11B, T24 Pt 2
n/a
Wildland-urban interface
2025 CA-WUIC, T24 Pt 7 based on 2024 IWUIC
n/a
Historical buildings
2025 CHBC, T24 Pt 8
n/a
Administrative
2025 CAC, T24 Pt 1
n/a
Zoning
No state-adopted code
Local zoning ordinance (city or county), subject to state preemptionLocal text supersedes the state code
Unincorporated communities San Mateo County reviews
These communities have no city building department of their own. The county is the authority having jurisdiction, so this page's code stack is the one that applies.
North Fair Oaks · Emerald Hills · La Honda · Loma Mar · Montara · Moss Beach · El Granada · Princeton-by-the-Sea · Pescadero · San Gregorio · West Menlo Park · Highlands-Baywood Park
What San Mateo County actually amended
Quoted from the adopted ordinance. These are the provisions that differ from the state code, which is where most correction lists come from. Excerpts, not the whole ordinance. Follow the source link for the full text.
CHAPTER 10.68- · EXCAVATING, GRADING, FILLING AND CLEARING
SECTION 10.68.010 - Scope and Purpose.
It is the declared intent of the County of San Mateo to promote the conservation
of natural resources, including topography and vegetation, as well as to protect
health and safety, which includes the reduction or elimination of the hazards of
earth slides, mud flows, rock falls, undue settlement, erosion, siltation, and
flooding, or other special conditions. To achieve these goals, the adverse
effects of grading, cut and fill operations, land clearing, water runoff, and soil
erosion must be minimized. […]
SECTION 3. · SECTION 3
A new Title 10 is hereby added to the San Mateo County Ordinance Code to be
numbered and entitled and to read as follows:
TITLE 10 - BUILDING REGULATIONS
ARTICLE 1 - GENERAL PROVISIONS
CHAPTER 10.04 - ADMINISTRATION
SECTION 10.04.000 – Adoption of the 2025 Administrative and
Reference Code.
The adopted editions of the 2025 Administrative Code, Title 24, Part 1, and
2025 Reference Code, Title 24, Part 12, are hereby adopted and incorporated
by reference. In addition, all amendments, errata, and/or emergency
supplements are also adopted during this triennial California Building Standards
Code cycle. […]
SECTION 1. · SECTION 1
ORDINANCE NO. 4916
BOARD OF SUPERVISORS, COUNTY OF SAN MATEO,
STATE OF CALIFORNIA
* * * * * *
AN ORDINANCE: (1) REPEALING TITLE 10 (BUILDING REGULATIONS) OF THE
SAN MATEO COUNTY ORDINANCE CODE; AND (2) ADOPTING A NEW TITLE
10 (BUILDING REGULATIONS), ADOPTING BY REFERENCE THE 2025
EDITION OF THE CALIFORNIA BUILDING STANDARDS CODE (TITLE 24,
PARTS 1 THROUGH 12) AND THE 2024 INTERNATIONAL PROPERTY
MAINTENANCE CODE, INCLUDING LOCAL AMENDMENTS
The Board of Supervisors of the County of San Mateo, State of
California, ORDAINS as follows:
WHEREAS, California Health and Safety Code Section 17958 requires
that cities and counties adopt building regulations that are substantially the
same as those… […]
Mapped hazard and district overlays stack on top of the adopted code. These are the overlays recorded for San Mateo County. They apply by parcel, not jurisdiction-wide, so confirm the parcel before assuming one is in play. Check CAL FIRE's fire hazard severity viewer and FEMA's flood map service.
Very High Fire Hazard Severity Zone
FEMA mapped flood hazard area
State law that overrides local zoning here
When one of these applies, the state statute governs over a conflicting local standard. This is the most common reason a local rule someone quotes you turns out not to be enforceable against a project.
Gov. Code 66310 et seq.
State ADU law preempts local zoning that would preclude a conforming ADU/JADU.
Applies when: project includes an ADU or JADU
Gov. Code 65915
State Density Bonus Law concessions/waivers override local development standards.
Applies when: project requests a density bonus
Gov. Code 65852.21 / 66411.7
SB 9 urban lot split / two-unit ministerial approval preempts conflicting local standards.
Applies when: project is an SB 9 lot split or two-unit development
San Mateo County enforces 2025 CBC, T24 Pt 2 based on 2024 IBC, the edition adopted statewide in California, amended locally in 2 disciplines.
Does San Mateo County amend the California code?
Yes: building, zoning.
Where do I confirm the code edition for a San Mateo County permit?
With the county building department that will review the permit. Adoption ordinances are amended on a local schedule, and a set submitted days apart can fall under different editions during a changeover.
Knowing the adopted edition is the easy half. Architechtura reads your drawings, resolves which of these provisions actually apply to the project, and returns the corrections a plan checker would write up, each one cited to the section it came from.
Compiled from published state and municipal adoption ordinances. Local governments amend their codes on their own schedule, and a pending ordinance can change what applies to your permit. Confirm the governing edition with the building department before you submit. This page is reference information, not a code determination.