San Mateo County, California Building Permit Guide

The County of San Mateo Planning and Building Department issues planning and building permits for unincorporated San Mateo County. If a project needs both, the planning permit must be obtained before applying for the building permit. The Department is at 455 County Center, 2nd Floor, Redwood City, CA 94063, open Monday - Thursday 8:00 am - 4:00 pm (closed 12:00 pm - 1:00 pm) and closed Friday - Sunday; Planning is (650) 363-1825.

This guide covers unincorporated San Mateo County and the City of San Mateo, the county’s largest city. Redwood City’s website could not be checked, so contact the city directly for work there.

The urban Midcoast building permit cap

Under the Local Coastal Program, the County may issue at most 40 housing unit building permits a year, ADUs included, in the urban Midcoast. Because of permits issued at the end of 2025, the County is not accepting building permit applications for new residential units there until January 1, 2028, or until an LCP amendment is approved.

Who handles permitting in San Mateo County?

Census estimates list twenty incorporated cities and towns in the county, which run their own permitting; the four most populous are San Mateo, Daly City, Redwood City and South San Francisco.

Projects in or over State highway rights of way also need a Caltrans permit.

San Mateo County permit costs and fees

From the Building Service Fee Schedule (effective April 1, 2026):

• Application filing fee: $60 for Easy Review, $298 for Moderate Review, $595 for Full Review.
• Minimum permit fee: $197 residential, $392 commercial.
• New residential buildings and additions: $8.33 per square foot, covering processing, plan review and inspection; 50% is due when the application is accepted and the rest before issuance.
• Plan reviews beyond three rounds cost 1/3 of the original plan check fee per resubmittal.

The County’s Affordable Housing Impact Fee for a single-family detached home is $0 per square foot for the first 2,500 sq ft of net new residential floor area and $5.00 per square foot over 2,500.

Septic systems and wells in San Mateo County

Parcels served by a septic system or a private domestic well need Environmental Health Services review for planning and building projects, and anyone installing an individual water supply or sewage disposal system must have a permit from Environmental Health. The only approved onsite wastewater system in the county is a septic system; the County OWTS Ordinance took effect on February 4, 2016 and is applied through the Onsite Systems Manual (updated October 2025).

Encroachment permits in San Mateo County

Public Works encroachment applications are accepted only online through Accela Citizen Access; allow at least 5-7 working days. Contractors working in the County right of way must hold a Class A, C-12, C-34, C-42 or C-8 (concrete only) license. The package needs a site plan, a traffic control plan to CA MUTCD standards, and a surety bond for mainline and trenchless construction.

Inspections in San Mateo County

Permits are applied for and tracked in the County’s Accela Citizen Access portal, and inspections are scheduled online through the permit record. Inspections take place between 8:00 am and 3:30 pm; after 7:30 am on the day, a 3-hour estimated time window is posted online. Each inspection must be scheduled separately. Questions go to buildinginspections@smcgov.org or (650) 599-7311.

Building permits in the City of San Mateo

The City of San Mateo requires a building permit to build, enlarge, alter, remove, demolish or repair a structure in the city. For permit requirements, call a permit technician at (650) 522-7172; City Hall is at 330 West 20th Avenue.

Official San Mateo County permitting resources

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

• County Planning and Building
• Apply for a permit
• Planning and Building fees
• Urban Midcoast building permit cap
• Schedule an inspection
• Partnered agencies
• Public Works permits
• Onsite wastewater treatment systems
• City of San Mateo building permits

Frequently asked questions

Can I apply for a new house in the urban Midcoast?

Not until January 1, 2028, or until an LCP amendment is approved; the County is not accepting building permit applications for new residential units there.

Do I need my planning permit first?

Yes. If a project needs both, the planning permit must be obtained before you apply for the building permit.

When is the County building counter open?

Monday - Thursday 8:00 am - 4:00 pm, closed 12:00 pm - 1:00 pm, and closed Friday - Sunday.

Simplify San Mateo County permitting with Alliance Permitting

• Check whether the parcel is in a city or on county land, and which county offices beyond Building must sign off
• Line up septic, well, encroachment and fire approvals so they do not hold up the building permit
• File in the county portal, track review rounds and book inspections against the county’s cut-off times

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.