Zoning, building permits and septic rules in San Carlos, California
San Carlos is a city in San Mateo County, California. San Carlos adopts its own zoning, so inside its limits San Carlos’s rules apply, not the county’s. 6 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 San Carlos
San Carlos’s own rules
Building permitRequired
Mechanical, structural, plumbing and electrical work on property inside San Carlos city limits
Exempt per the same page: wood retaining walls 3 feet tall or shorter; concrete or masonry walls less than 4 feet tall measured from bottom of footing; painting and wallpapering; side or rear yard fences 6 feet high or less; freestanding single-story sheds not attached to other buildings under 120 sq ft (planning division setbacks and height still apply).
Pools, spas and hot tubs require building permits and security fencing.
Work in the city right-of-way (fences, retaining walls, storm drain connections) needs a separate encroachment permit from Public Works.
The page says that if a project needs a permit, questions go to building@cityofsancarlos.org.
freestanding shed exemption threshold (no building permit below this size): < 120 sq ft (planning division setbacks, height and location limits still apply)
“in general, any mechanical or structural work (e.g., cabinets, doors, windows, roofs), plumbing work (e.g., sinks, irrigation, water heaters), or electrical work (e.g., appliances, furnaces, garage door openers, pool pumps) require a building permit.”
Owner-builder exemptionAvailable
Owner-occupied home inside San Carlos city limits
Owner-occupied home only, as the quoted text states.
The page adds that a contractor the owner hires must be licensed and maintain proper insurance and business license.
The page does not state whether an owner-builder exemption applies to a new home on a non-owner-occupied lot.
“yes, work on an owner-occupied home may be performed by the owner.”
Building code adoptedAdopted
Building construction inside San Carlos city limits
The city's Building Division page lists 'California building codes online 2025' among its adopted codes, together with local ordinances, and separately lists a wildland-urban interface code and CALGreen checklists.
The page also states: 'as a result of recent court decisions, the city of san carlos is currently not enforcing regulations that prohibit natural gas infrastructure in new buildings.'
“the building permit is based upon the california building codes, which were adopted (in addition to local ordinances) to protect health, general welfare and the investment in your property.”
InspectionsRequired
Permitted construction inside San Carlos city limits
The page describes the Building Division's final inspection sign-off as the step a homeowner should wait for before releasing final payment; the inspection schedule and stages were not stated on this page.
“it is a good idea to arrange with your contractor to hold the last substantial payment until the building division signs off on the final inspection.”
Local zoningPresent
Land inside San Carlos city limits (not the unincorporated county area)
Presence is shown by the city's own zoning-chapter ADU ordinance (Section 18.23.210 of the San Carlos zoning code, Title 18), which HCD reviewed. The full zoning code (Title 18 district tables) was not opened because codepublishing.com returned HTTP 403 during this run.
“accessory dwelling units shall satisfy applicable objective design criteria and conform to any applicable objective design guidelines of the underlying zoning district.”
Permit processPartial
Building permit application process inside San Carlos city limits
Applications go through the city's online self-service portal, but the page says a completed one-page building permit application form must still be uploaded on the attachments section.
Questions about whether a project needs a permit go to building@cityofsancarlos.org with the property address.
Process for new construction is said to vary by project and is covered on a separate page that was not opened.
“visit the new customer self-service portal to create a user profile and start submitting your permit applications directly through the portal.”
Still unanswered
We looked and could not find an official answer yet. Silence is not permission; ask San Carlos or San Mateo County directly.
Certificate of occupancy — New dwelling occupancy inside San Carlos city limits
Zoning districts — Zoning district map and list for San Carlos city
Minimum dwelling size — Minimum dwelling size for a single-family home in the main residential district of San Carlos city
Minimum lot size — Minimum lot size in the main single-family residential district of San Carlos city
Setbacks — Yard setbacks in the main single-family residential district of San Carlos city
18 more unanswered
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
Subdividing land
Driveway access
Building in a floodplain
Short-term rentals
Permit fees
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 San Carlos 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 San Carlos means bringing your own water and power. The kit we’d start with:
