Zoning, building permits and septic rules in Foster City, California
Foster City is a city in San Mateo County, California. Foster City adopts its own zoning, so inside its limits Foster City’s rules apply, not the county’s. 5 rules below are quoted from official sources and independently re-checked, most recently on October 22, 2026. Rules for unincorporated land are on the San Mateo County page.
Answers from the rulebook for Foster City
Foster City’s own rules
Building code adoptedAdopted
Building construction inside Foster City city limits under the city's adopted California building codes (2025 editions) in Foster City Municipal Code Chapter 15.02 and related chapters.
The city lists the 2025 California Building Code (Volumes 1 and 2), 2025 Existing Building Code, 2025 Residential Code, 2025 Electrical, Mechanical, Plumbing and Fire Codes, 2025 Historical Building Code and 2025 CALGreen as adopted, with local amendments under Foster City Municipal Code Chapter 15.02.
The city page states the 2025 California Building Code is in effect from January 1, 2026 and is not affected by the AB-130 residential code freeze (October 1, 2025 to June 1, 2031), which allows exceptions for emergency health and safety standards, fire safety, water conservation, home hardening and local amendments aligned with a pre-June 2025 general plan.
The adopting ordinance number and text for the 2025 codes were not located in this run.
“the 2025 california building code (adopted before the freeze) is in effect from january 1, 2026, and is not affected by the moratorium.”
InspectionsRequired
Construction and demolition work inside Foster City city limits.
A pre-construction inspection must be scheduled after the permit is issued, with 24-hour minimum notice via eTRAKiT.
Building Inspections page lists building inspection hours (Monday-Friday) and says past inspection results are viewable in eTRAKiT.
Final inspection and job card sign-off requirements were not opened in this run.
“before beginning any construction or demolition, you must schedule a pre-construction inspection. this inspection should be scheduled only after your permit has been issued.”
Local zoningPresent
Land inside Foster City city limits: the city's own Title 17 (Zoning) of the Foster City Municipal Code governs zoning.
Dimensional and district rules were not opened in this run (see unknown claims).
Accessory dwelling units (ADU) and junior ADUs on residential lots inside Foster City city limits, including single-family lots in R-1.
ADUs are allowed in all residential zoning districts per the city ADU page.
Single-family lot options are listed under Foster City Municipal Code section 17.78.060.A (option #2 is one ADU up to 850 square feet, conversion, attached or detached).
The city ADU page says Ordinance No. 692 (adopted August 18, 2025) amended Chapter 17.78; that ordinance text was not opened in this run.
Ordinance text and the full option list were not fully verified beyond the excerpts shown.
junior ADU maximum size: <= 500 square feet · ADU maximum size (conversion, attached or detached): <= 850 square feet (per option #2 on the city ADU page)
“adus are allowed in all residential zoning districts. residential districts in foster city include: r-1, r-2, r-t, r-3, r-4.”
Subdividing landRegulated (with conditions)
Subdivision of land inside Foster City city limits under the city's Title 16 (Subdivisions) of the municipal code.
Subdivision standards and procedures were not opened in this run.
We looked and could not find an official answer yet. Silence is not permission; ask Foster City or San Mateo County directly.
Owner-builder exemption — Owner-builder permit exemption inside Foster City city limits.
Certificate of occupancy — Certificate of occupancy for new or altered dwellings inside Foster City city limits.
Zoning districts — Zoning district map and use tables for land inside Foster City city limits.
Minimum dwelling size — Minimum dwelling size for the main single-family residential district (R-1) inside Foster City city limits.
Minimum lot size — Minimum lot area in the main single-family residential district (R-1) inside Foster City city limits.
19 more unanswered
Setbacks
Lot coverage
Building height
Living in an RV
Camping on your land
Tiny homes
Manufactured homes
Who permits septic
Septic permit
Septic inspection
Off-grid sanitation
Well permit
Mandatory utility hookup
Agricultural exemption
Driveway access
Building in a floodplain
Short-term rentals
Permit fees
Permit process
Each answer was extracted from an official source and independently re-checked against that source by a second reviewer. That is an evidence check, not legal advice. Rules change; confirm with the authority before you buy or build.
Unanswered questions are usually a sign that Foster City publishes no rule on the point, not that none exists. San Mateo County’s page lists the county offices to call.
Off-grid gear
Going off-grid in Foster City means bringing your own water and power. The kit we’d start with:
