Bolthole Index

San Mateo County, California

Building permits, zoning and septic rules in San Mateo County, California

35Index Score / 100
#39 of 58 in California

Unincorporated San Mateo County, California requires a building permit before you erect, enlarge, alter, repair, move or demolish a building or structure12. The county also zones unincorporated land through its own Zoning Ordinance, separate from the zoning that cities like Half Moon Bay or San Mateo set inside their own limits34. Septic systems are permitted separately, by Environmental Health Services, and only about 16.3% of the county's soils have no severe limits for a conventional drain field56.

At a glance

Building permit
Required in unincorporated San Mateo County1
Zoning
Yes — a countywide Zoning Ordinance covers unincorporated land; cities zone separately3
Septic permits
Issued by San Mateo County Environmental Health Services5
Owner-builder
Allowed under state law with conditions; a permit and an owner-builder declaration are still required7
Driveway / encroachment permit
Required for a new or altered driveway in the county road right-of-way; $146–$7628
Floodplain development
FEMA flood zones outside Zone X need at least 1 foot of freeboard and, often, an Elevation Certificate9
Wells
A drilling permit from Environmental Health Services is required10
Bolthole Index score
35.44/10011

Who to call

Building permits

San Mateo County Planning and Building Department – Building Division

Building permit applications, plan review and inspections in unincorporated San Mateo County

(650) 599-7310

[email protected]

455 County Center, 2nd Floor, Redwood City, CA 94063

Zoning

San Mateo County Planning and Building Department – Planning Division

Zoning determinations, zoning-district information, rezoning and land-use review for unincorporated San Mateo County

(650) 363-1825

[email protected]

455 County Center, 2nd Floor, Redwood City, CA 94063

Septic permits

San Mateo County Environmental Health Services

Septic (OWTS) permits, site evaluations, and water-well drilling permits for San Mateo County

(650) 372-6200

Floodplain permits

San Mateo County Planning and Building Department – Floodplain Management

Floodplain development permits and Elevation Certificate review for unincorporated San Mateo County; reachable through the Planning Division at (650) 363-1825

Roads & driveways

San Mateo County Department of Public Works

Encroachment (driveway) permits for work within the county road right-of-way in unincorporated San Mateo County

Contact details are copied from each office’s official page and were checked against it on September 27, 2026.

Do you need a building permit in San Mateo County, California?

Yes. Unincorporated San Mateo County requires a permit before a building or structure is erected, constructed, enlarged, altered, repaired, moved, improved, removed, converted or demolished12. This mirrors state law: California requires a separate permit for each building or structure from the local building official before work starts, and code requirements vary by city and county12. The county's own guidance points applicants to pages 12–18 of its Building Ordinance to check whether specific work is exempt213. California lets an owner build their own home without a contractor license under limited conditions — for example, a homeowner improving a principal residence must have lived there for the 12 months before completion, and cannot have used the exemption on more than two structures in a three-year period — but this only removes the licensing requirement, not the permit714. If your parcel is inside a city rather than unincorporated territory, that city's own building department handles permitting instead2.

Who is the San Mateo County building department, and how do you reach them?

The Planning and Building Department's Building Division reviews and inspects construction projects that require building permits in unincorporated San Mateo County, from an office at 455 County Center, 2nd Floor, Redwood City1513. Reach the building counter at (650) 599-7310 or [email protected], and inspections at (650) 599-7311; the office is open Monday through Thursday, 8:00 am to 4:00 pm, closed for lunch from noon to 1:00 pm, and closed Friday through Sunday13. The county's Building Service Fee Schedule took effect April 1, 2026, and a separate Affordable Housing Impact Fee applies to residential projects: a single-family home adds up to 2,500 square feet at no impact-fee charge, while projects over 3,500 square feet of net new floor area pay the fee on the full total16. Zoning questions go to the Planning Division at (650) 363-1825, in the same building17.

Does San Mateo County have zoning?

Yes. The County Zoning Ordinance regulates growth and development across unincorporated San Mateo County, and the county's own GIS layer, labeled "Unincorporated SMC Zoning," is how staff and applicants confirm a parcel's zoning district318. Zoning inside incorporated cities is a separate matter entirely — the county does not provide zoning information for parcels within city limits, so a buyer near a city line should confirm with that city's planning department, not the county4. A single parcel can carry more than one zoning layer at once — a base district plus overlays such as S (development standards), CD (coastal zone) or DR (design review) — and must comply with each19. In one specific area, the Devonshire neighborhood's S-102 combining district, county code sets a 20,000-square-foot minimum building site, a 75-foot minimum average site width, and a 30-foot maximum building height (up to 36 feet case-by-case for remodels); those numbers apply only where S-102 is combined with a residential district, not countywide2021.

How do septic permits work in San Mateo County?

Septic systems are not handled by the building department — San Mateo County Environmental Health Services administers local oversight of onsite wastewater treatment systems (OWTS) under its Local Agency Management Program, and anyone installing an individual water supply or sewage disposal system needs a permit from Environmental Health first5222324. Inspection staff observe and approve the work whenever a system is installed, repaired, altered or destroyed25. Statewide, California's OWTS Policy lets counties run their own approved local program as long as it stays consistent with state standards, which is what San Mateo County does26. Soils matter here: only about 16.3% of San Mateo County's soils have no severe limitations for a conventional drain field, so most parcels will need Environmental Health's site evaluation before you can count on a standard system, and an alternative or engineered design is common6. Where there is no municipal sewer, the county states plainly that a septic system is the only approved way to dispose of sewage and wastewater on your own property27.

Can you live in an RV or tiny home on your land in San Mateo County?

Not as a general rule. California treats RVs as units for temporary occupancy, not permanent dwellings, and limits RV occupancy to mobilehome parks or special occupancy parks unless a local ordinance says otherwise; we could not confirm a San Mateo County ordinance allowing full-time RV living on a private unincorporated parcel, so ask the Planning Division before relying on an RV for housing2817. A tiny home can be occupied only if it qualifies as one of a specific list of structure types — a HUD-code manufactured home, a California Residential or Building Code home, factory-built housing, an RV, a park trailer, or a camping cabin — and is sited where that type is allowed; a tiny home that fits none of those categories is a noncomplying structure29. One narrow local exception exists: tiny homes can count as housing units in projects funded through the county's Farm Labor Housing Loan Program, but only as rental housing for eligible farm laborers, not for a landowner's personal use30. We could not confirm a county-specific minimum dwelling floor area for unincorporated San Mateo County; state law lets a local jurisdiction, by its own ordinance, permit efficiency units as small as 150 square feet for up to two occupants, but whether San Mateo County has adopted that ordinance is unconfirmed — ask the Planning Division3117.

Building a home in San Mateo County: the steps, in order

  1. Confirm the parcel is unincorporated and pull its zoning district(s) through the county's GIS zoning layer1718.
  2. If the site will use a well or septic, contact Environmental Health Services early for a site evaluation2423.
  3. If the parcel is in a FEMA flood zone other than Zone X, plan for an Elevation Certificate at plan check, at framing inspection, and before occupancy32.
  4. Submit the building permit application to the Building Division, filing an owner-builder declaration if you're not hiring a licensed contractor13714.
  5. Pay the Building Service Fee Schedule charges and, for larger homes, the Affordable Housing Impact Fee16.
  6. Complete plan review and pass the required inspections, ending with a Final Inspection before occupancy1513.
  7. If you're building or altering a driveway onto a county road, get an encroachment permit from the Department of Public Works338.

What to check before you buy land in San Mateo County

San Mateo County is expensive and densely settled: the typical home value is about $1,595,764, population density runs around 1,619 people per square mile, and the nearest city of 100,000 or more is roughly 11 miles from the county's center343536. Only 4.6% of the county is federal land, and 51.6% of the land is at 15% slope or less, so terrain deserves a parcel-level review3738. Check septic suitability before you fall in love with a parcel — just 16.3% of soils here have no severe limits for a conventional drain field6. Ask the Floodplain Management team whether a parcel sits in a mapped flood zone, since anything but Zone X requires at least a foot of elevation above base flood399. The county gets about 28.7 inches of rain a year, with severe drought in roughly 31.9% of years4041. Budget for an effective property tax rate near 0.6%, a median tax bill around $9,167 a year, and a typical home insurance premium near $1,768424344. San Mateo County's Bolthole Index score is 35.44 out of 10011.

Watch-outs

  • We could not confirm whether unincorporated San Mateo County has adopted its own minimum dwelling floor-area ordinance; ask the Planning Division before assuming state minimums apply17.
  • Full-time RV living on your own unincorporated parcel is not established as allowed; California limits RV occupancy to mobilehome or special occupancy parks unless a local ordinance says otherwise, and none was confirmed here2817.
  • Most San Mateo County soils are not well suited to a conventional septic drain field — get a site evaluation from Environmental Health Services before you count on standard septic624.

Sources

  1. Apply for a Permit (2026 county census)
  2. Apply for a Permit, quoted and re-checked
  3. San Mateo County | Zoning (2026 county census)
  4. Get Zoning Information, quoted and re-checked
  5. Land Use, Septic & Wells (2026 county census)
  6. Share of soils without severe limits for a conventional septic drain field (USDA SSURGO): Bolthole Index county data
  7. California Contractors State License Board - Owner-Builder Overview (2026 county census)
  8. Driveway Permit, quoted and re-checked
  9. Flood Elevation Certificate, quoted and re-checked
  10. Land Use, Septic & Wells, quoted and re-checked
  11. Bolthole Index score (off-grid/homestead land score): Bolthole Index county data
  12. Do I need a building permit for my project? (California statewide rule), quoted and re-checked
  13. San Mateo County Planning and Building Department – Building Division (smcgov.org)
  14. Owner-Builder Overview, quoted and re-checked
  15. Building, quoted and re-checked
  16. Building Permit Fees, quoted and re-checked
  17. San Mateo County Planning and Building Department – Planning Division (smcgov.org)
  18. San Mateo County | Zoning, quoted and re-checked
  19. Get Zoning Information, quoted and re-checked
  20. Title 8 – Zoning & Development Code, quoted and re-checked
  21. Title 8 – Zoning & Development Code, quoted and re-checked
  22. Land Use, Septic & Wells, quoted and re-checked
  23. Land Use, Septic & Wells, quoted and re-checked
  24. San Mateo County Environmental Health Services (smcgov.org)
  25. Land Use, Septic & Wells, quoted and re-checked
  26. Water Quality Control Policy for Siting, Design, Operation and Maintenance of Onsite Wastewater Treatment Systems (OWTS Policy) (California statewide rule), quoted and re-checked
  27. Land Use, Septic & Wells, quoted and re-checked
  28. Information Bulletin 2016-01: Tiny Homes (California statewide rule), quoted and re-checked
  29. Information Bulletin 2016-01: Tiny Homes (California statewide rule), quoted and re-checked
  30. Farm Labor Housing Loan Program, quoted and re-checked
  31. California Health and Safety Code Section 17958.1 (California statewide rule), quoted and re-checked
  32. Flood Elevation Certificate, quoted and re-checked
  33. San Mateo County Department of Public Works (smcgov.org)
  34. Typical home value (Zillow): Bolthole Index county data
  35. Population density: Bolthole Index county data
  36. Distance to the nearest metro area: Bolthole Index county data
  37. Federal land share: Bolthole Index county data
  38. Share of land at 15% slope or less: Bolthole Index county data
  39. San Mateo County Planning and Building Department – Floodplain Management (smcgov.org)
  40. Annual precipitation: Bolthole Index county data
  41. Share of years in severe drought: Bolthole Index county data
  42. Effective property tax rate: Bolthole Index county data
  43. Median property tax bill: Bolthole Index county data
  44. Typical home insurance premium: Bolthole Index county data

Written September 27, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.

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County locator

San Mateo County in California

35
County map
San Mateo County highlighted among the California counties · colored by Index score

How San Mateo County scores

Seclusion13100% ev.
Self-Sufficiency60100% ev.
Admin Boringness41100% ev.
Durability40100% ev.
Property Autonomy56100% ev.
Carry Cost44100% ev.

Evidence strength: 100%. This reports direct-source completeness and fallback use; it is separate from the score and is not a confidence interval. How it works →

$1596kTypical home
0.6%Property tax
$12,311Land / acre
28.7"Annual rain
31.9% of yrsSevere drought
0.7 / yr (+0.4)Mid-century 100°F days
63.8 daysMid-century dry spell
2.08" (+7.6%)Mid-century 1-day rain
1.07×Wildfire change factor
100%Forward climate coverage
$1,768Home insurance / yr
3.4% / yrInsurance growth
0.6%Nonrenewal rate
county median (2+ published ZIPs)Insurance basis
6,410,169People within 2 hr
722,806Radius comparison (15 mi)
1,619.1People / sq mi
4.6%Federal land
51.6%Land at 15% slope or less
16.3%Septic soil without severe limits
31,843 acWorkable land screen
175.7 tonsBiomass / forest ac
57.1°FAvg temp

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Answers from the rulebook for San Mateo County

What the ordinances and state agencies actually say — one answer per question, each quoted from the official source and independently re-checked.

San Mateo County rules

  • Building permitRequired

    Buildings and structures in unincorporated San Mateo County that are erected, constructed, enlarged, altered, repaired, moved, improved, removed, converted, or demolished.

    • The County page directs applicants to pages 12-18 of the Building Ordinance to determine whether particular work is exempt from a permit.
    • The County states that incorporated cities and towns administer their own permitting; this claim is limited to unincorporated areas.
    “Needed if a building or structure will be erected, constructed, enlarged, altered, repaired, moved, improved, removed, converted, or demolished.”
  • InspectionsRequired

    Construction projects in unincorporated San Mateo County that require building permits.

    • The type and timing of required inspections depend on the building permit type.
    • Inspections generally include initial inspections and a Final Inspection once all work under the permit is complete, before occupancy or use of the impacted area.
    • Each inspection must be scheduled separately.
    “We review and inspect all construction projects that require building permits in the unincorporated areas of San Mateo County.”
  • Certificate of occupancyLimited

    Certificate-of-occupancy issuance for development in FEMA-designated flood zones in unincorporated San Mateo County, excluding Moderate to Low Risk Areas designated Zone X.

    • Applicants in all FEMA-designated flood zones except Zone X must demonstrate compliance with applicable flood-development standards.
    • Habitable and utility areas must be at least one foot above the base flood elevation.
    • Areas below the base flood elevation are limited to garage and/or crawlspace purposes constructed according to currently adopted and enforced building regulations.
    • An Elevation Certificate must be provided at plan check, during construction at framing inspection, and completed and approved at final inspection or before issuance of the Certificate of Occupancy.
    • Additional regulations apply under Chapter 35.5, Flood Hazard Areas, of the Zoning Regulations.

    minimum elevation above base flood elevation: >= 1 foot (applies to habitable and utility areas) · Elevation Certificate stages: plan check; framing inspection; final inspection or before Certificate of Occupancy

    “The Elevation Certificate (EC) is a three step process that must be completed before a certificate of occupancy can be issued.”
  • County-wide zoningPresent (with conditions)

    County zoning ordinance and zoning districts in unincorporated San Mateo County.

    • The County Zoning Ordinance regulates growth and development in the county's unincorporated territory.
    • The county's zoning information page identifies an Unincorporated SMC Zoning layer and states that development must comply with each applicable zoning-district regulation.
    • The County Ordinance Code page states that the replacement ordinance is not yet effective in the coastal zone while under Coastal Commission review.
    “Put a check mark in the check box labeled Unincorporated SMC Zoning to display Zoning Districts.”
  • Local zoningVaries (with conditions)

    Aggregate local zoning across San Mateo County, combining county zoning for unincorporated areas with zoning administered by incorporated municipalities; this claim does not attribute municipal ordinances to San Mateo County.

    • The County source expressly identifies its zoning controls as Unincorporated SMC Zoning.
    • Municipal parcels may be subject to the applicable municipality's zoning regulations rather than the county's unincorporated-area zoning regulations.
    • Within unincorporated areas, applicable parcels may have one, two, or several zoning districts and must comply with each applicable district regulation.
    • The replacement county ordinance is not yet effective in the coastal zone while under Coastal Commission review.
    “Zoning information for properties within the unincorporated County is provided by our Planning GIS program. Detailed instructions are also provided on our website. Zoning information is not provided for properties within city limits; please contact your city's Planning Department for more information.”
  • Zoning districtsPublished

    Zoning districts and related zoning layers for unincorporated San Mateo County parcels.

    • A parcel may have one, two, or several zoning districts.
    • Each zoning layer represents a distinct chapter or section in the County Zoning Regulations.
    • Development must comply with the regulation for each applicable district.
    • The County identifies S districts as containing development standards, R districts as primarily residential, RM, TPZ, and PAD districts as rural, CD as applying to all Coastal Zone areas, and DR as requiring design review standards.

    example zoning districts: RM; TPZ; R-1/S-101; R-1/S-17/DR/CD

    “Put a check mark in the check box labeled Unincorporated SMC Zoning to display Zoning Districts.”
  • Minimum lot sizeSpecified

    Parcels in any single-family residential district combined with the County S-102 Combining District (Devonshire) in unincorporated San Mateo County.

    • The S-102 standards apply only in a single-family residential district with which S-102 is combined.
    • A parcel may not be divided if the resulting building site would be less than the minimum required to maintain conformity with the district building-floor-area requirements.

    minimum building site area: 20000 sq ft · minimum average building site width: 75 ft

    “minimum building site area shall be 20,000 sq. ft.”
  • Building heightSpecified

    Buildings in any single-family residential district combined with the County S-102 Combining District (Devonshire) in unincorporated San Mateo County.

    • The S-102 standards apply only in a single-family residential district with which S-102 is combined.
    • For remodeling costing less than 50 percent of total replacement value, the maximum may increase to 36 feet, determined case-by-case by the Director of Planning and Building.
    • Chimneys, pipes, mechanical equipment, antennae, and other common facilities may extend beyond 28 feet to a maximum of 36 feet as required for safety or efficient operation.
    • Attached or detached downhill-slope garages allowed to extend into the front setback are subject to a 28-foot maximum and additional plate-height and story restrictions.

    maximum building height: 30 ft (Remodeling costing less than 50 percent of total replacement value may increase to 36 feet case-by-case.) · downhill-slope garage maximum height: 28 ft

    “maximum building height shall be 30 feet.”
  • Tiny homesLimited

    Tiny homes used as housing units in projects participating in the San Mateo County Farm Labor Housing Loan Program.

    • Project units must be located in San Mateo County.
    • Project units must be rented to eligible very-low-income farm laborers or farm laborers and their families meeting the program's agricultural-work criteria.
    • All project units must be used as rental housing for farm laborers for the duration of the loan term.
    • All projects must comply with applicable Planning and Building and Environmental Health requirements.
    • All applicable permit requirements apply.
    • The program is subject to funding availability and execution of a loan agreement.
    • The document states it was updated and published on 2025-10-22; this is not treated as an effective date.

    farm-labor agricultural employment: > 20 hours per week average (Eligible farm laborers must also earn at least half their income from agriculturally related work.) · maximum rent and utility allowance: <= 30 percent of gross income (The document states allowances must not exceed 30% of gross income.)

    “A housing unit can be a single-family home, mobile home, tiny home, or modular building.”
  • Who permits septicCounty

    Onsite wastewater treatment systems in San Mateo County.

    • San Mateo County Environmental Health administers local OWTS oversight through the County LAMP.
    • The LAMP operates under the State Water Resources Control Board OWTS Policy and was approved by the San Francisco Bay Regional Water Quality Control Board.
    “As such, it is intended to allow the County to continue providing local oversight of OWTS”
  • Septic permitRequired

    Installation of an individual sewage disposal system in San Mateo County.

    • Environmental Health reviews the application for safety to neighboring properties and surrounding areas.
    • Community members and/or the County Board of Supervisors may also need to approve installation of new systems.
    “All people who install individual water supplies or sewage disposal systems must have a permit from Environmental Health.”
  • Septic inspectionRequired

    Individual sewage disposal systems that are installed, repaired, altered, or destroyed in San Mateo County.

    • Environmental Health observes and approves the work.
    • Review includes the proposed location, soil testing, plans, construction, and safe destruction verification.
    “Inspection staff will observe and approve the work when you need to install, repair, alter or destroy an individual sewage disposal system.”
  • Off-grid sanitationLimited

    Sewage disposal on property where no municipal sewer system exists in San Mateo County.

    • If an area lacks a municipal sewer system, sewage and wastewater must be disposed of on the property.
    • The County page states that the only approved system in San Mateo County is a septic system.
    • A permit from Environmental Health is required for installation of an individual sewage disposal system, and Environmental Health observes and approves installation, repair, alteration, or destruction work.
    “If you live in an area of San Mateo County that does not have a municipal sewer system, you must dispose of sewage and wastewater on your own property. In San Mateo County, the only approved system is a septic system.”
  • Well permitRequired

    Drilling a water well in San Mateo County.

    • Before obtaining a drilling permit from Environmental Health Services, the applicant may first need Planning and Building approval or determination regarding a Coastal Development Permit or Coastal Development Exemption.
    • The permit is non-transferable and authorizes only the recorded water-well driller.
    • At least 2 full working days’ notice is required before drilling begins.
    • At least 2 full working days’ notice is required for pump-test, annular-seal, and final inspections.
    • Permit and inspection fees may apply; the cited procedure states the drilling permit fee covers site examination, annular well-seal verification, and processing time, while pump-test verification requires an additional fee.
    “Once you have received approval from the Planning and Building Department or determine that no CDP or CDX is needed, you’ll need a drilling permit from Environmental Health Services.”
  • Driveway accessRequired

    Replacing or constructing a new driveway within the right-of-way of San Mateo County unincorporated districts.

    • An encroachment permit from the San Mateo County Department of Public Works is required.
    • Replacing an existing driveway to the same grade and dimensions has a listed fee of $146.
    • A new driveway, or widening or regrading an existing driveway, has a listed fee of $762.

    existing driveway remove and replace to same grade and dimensions: 146 USD · new driveway or widening and/or regrading existing driveway: 762 USD

    “Replacing or constructing a new driveway within the right-of-way of San Mateo County's unincorporated districts requires an encroachment permit from the Department of Public Works.”
  • Building in a floodplainRequired

    Development in FEMA-designated flood zones and construction or other development within floodplains in unincorporated San Mateo County.

    • Applicants in all FEMA-designated flood zones except Moderate to Low Risk Areas designated Zone X must demonstrate compliance with development standards.
    • Habitable and utility areas must be at least one foot above the base flood elevation.
    • Areas below the base flood elevation are limited to garage and/or crawlspace purposes constructed according to currently adopted and enforced building regulations.
    • New construction must be anchored against movement by floodwaters, resistant to flood forces, constructed with flood-resistant materials, and flood-proofed or elevated so that the first floor of living space and all mechanical and services are at least one foot above the elevation of the 100-year flood.
    • These standards apply to new structures and substantial improvements of existing structures.
    • Most other types of development within the floodplain, including grading, cut and fill, riprap, and bank stabilization, also require a floodplain development permit.
    • The County defines substantial improvement as reconstruction, rehabilitation, or an addition whose cost exceeds 50% of the structure's value, using $300.00 per square foot as replacement cost.

    minimum elevation above base flood elevation: >= 1 foot · substantial improvement threshold: > 50 percent of structure value (Replacement cost uses $300.00 per square foot) · Zone X exception: Zone X (Moderate to Low Risk Areas designated Zone X are excepted from the NFIP compliance process described)

    “Additionally, most other types of development within the floodplain also require a floodplain development permit, such as grading, cut and fill”
  • Permit feesPublished

    Building permit and development-related fees administered by San Mateo County for unincorporated areas.

    • The Building Service Fee Schedule is identified as effective April 1, 2026.
    • Affordable Housing Impact Fees apply only to residential and non-residential development of certain types and sizes.
    • Projects up to and including 3,500 square feet of net new gross floor area are exempt from the Affordable Housing Impact Fee; projects over 3,500 square feet pay the fee on the total net new gross floor area.
    • The source states that various exemptions, waivers, and modifications may apply.

    fee schedule effective date: 2026-04-01 · single-family detached home, 1 unit housing impact fee for first 2,500 square feet: 0 USD per square foot ($5.00 per square foot over 2,500 square feet) · single-family detached home, 2 to 4 units housing impact fee for first 2,500 square feet: 5 USD per square foot ($12.50 per square foot over 2,500 square feet) · single-family detached home, 5 or more units housing impact fee: 15 USD per square foot · non-residential projects exempt threshold: <= 3500 square feet of net new gross floor area (Projects generating in excess of 3,500 square feet pay on the total net new gross floor area)

    “Building Service Fee Schedule Fee Schedule (effective April 1, 2026)”

California rules that apply here

  • Owner-builder exemptionAvailable (with conditions)

    Exemption from California contractor-licensing chapter for an owner-builder who builds or improves a structure on the owner’s property; this does not itself establish exemption from local building permits, inspections, or other code requirements.

    • For work personally performed by the owner or performed by the owner’s employees, none of the improvements may be intended or offered for sale, and employee compensation must be wages as their sole compensation.
    • For work directly contracted to licensed trade contractors, the owner must directly contract with licensees duly licensed for the respective trades.
    • For single-family residential structures under the licensed-contractor arrangement, no more than four structures may be intended or offered for sale in a calendar year; this limitation does not apply if the owner contracts with a general contractor for construction.
    • For a homeowner improving a principal residence or its appurtenances, the work must be performed before sale, the homeowner must have actually resided in the residence for the 12 months before completion, and the homeowner must not have used this exemption on more than two structures more than once during any three-year period.
    • A nonprofit corporation may qualify when assisting an owner-builder participating in a mutual self-help housing program.
    • Sale or offering for sale within one year after completion creates a rebuttable presumption that the structure was undertaken for sale; sale or offering for sale of five or more structures within one year creates a conclusive presumption.
    • This is a contractor-licensing exemption and should not be treated as a building-permit exemption.

    single-family structures intended or offered for sale: <= 4 structures per calendar year (Does not apply if the owner contracts with a general contractor for construction.) · prior residence occupancy: >= 12 months before completion (Applies to the principal-residence homeowner exemption.) · owner-builder exemption use: <= 2 structures during any three-year period (The statute states the homeowner has not availed himself or herself of the exemption on more than two structures more than once during any three-year period.) · sale presumption period: 1 year after completion (Sale or offering for sale creates a rebuttable presumption; five or more structures creates a conclusive presumption.) · conclusive-presumption threshold: >= 5 structures within one year after completion (Structures sold or offered for sale by the owner-builder.)

    “This chapter does not apply to any of the following: (1) An owner who builds or improves a structure on his or her property”
    3 more reviewed findings on this topic
    • Conditional — California Contractors State License Law exemption for qualifying owner-builders, including qualifying projects in San Mateo County.
      “An owner-builder is exempt from licensure, but there are limitations.”
    • Conditional — Owners who build or improve structures on their own property, and homeowners improving their principal residence or appurtenances, subject to Business and Professions Code section 7044.
      “(a) This chapter does not apply to any of the following: (1) An owner who builds or improves a structure on his or her property”
    • Available (with conditions) — California contractor-licensing requirements for an owner who builds or improves a structure on the owner’s property; this is not stated as an exemption from building permits, inspections, or other code requirements.
      “This chapter does not apply to any of the following: (1) An owner who builds or improves a structure on his or her property”
  • Building code adoptedAdopted (with conditions)

    California Building Standards Code, California Code of Regulations, Title 24, including the 2025 California Building Code and related parts, for buildings and structures subject to the state code.

    • The 2025 California Building Standards Code applies to buildings and structures with a permit application date on or after January 1, 2026.
    • The applicable local building department or enforcing agency determines how the permit application date is established in a specific jurisdiction.
    • The code includes multiple parts, including the California Building Code, California Residential Code, Existing Building Code, Electrical Code, Mechanical Code, Plumbing Code, Energy Code, Wildland-Urban Interface Code, Fire Code, and Green Building Standards Code.

    effective date: 2026-01-01 · permit application date: >= 2026-01-01

    “The 2025 California Building Standards Code (CBSC), California Code of Regulations (CCR), title 24, will become effective on January 1, 2026, as a result of the 2024 Triennial Code Adoption Cycle. [...] The 2025 CBSC applies to all buildings and structures with a permit application date on or after January 1, 2026.”
    One more reviewed finding on this topic
    • Adopted — California statewide building standards, including residential construction subject to Title 24 of the California Code of Regulations.
      “Except as otherwise specifically provided by law, the building standards adopted and submitted by the department for approval [...] shall be adopted by reference”
  • Minimum dwelling sizeSpecified

    Efficiency units permitted by a California city, county, or city and county.

    • The local jurisdiction must adopt an ordinance permitting the efficiency unit.
    • Occupancy is limited to no more than two persons.
    • The unit may have partial kitchen or bathroom facilities as specified by the local ordinance.
    • All other applicable minimum standards under Health and Safety Code Part 1.5 continue to apply.

    minimum floor area: >= 150 square feet · maximum occupancy: <= 2 persons

    “Notwithstanding Sections 17922, 17958, and 17958.5, a city, county, or city and county may, by ordinance, permit efficiency units for occupancy by no more than two persons which have a minimum floor area of 150 square feet and which may also have partial kitchen or bathroom facilities, as specified by the ordinance.”
  • SetbacksSpecified

    Qualifying SB 9 housing developments in single-family residential zones, including development of up to two primary residential units, subject to the cited statutory eligibility requirements and local ministerial review.

    • The parcel must be located in a single-family residential zone.
    • The project must involve no more than two residential units.
    • Objective standards may be applied only if they do not physically preclude the statutory housing objectives, subject to the stated exceptions.
    • No setback may be required for an existing structure or a structure constructed in the same location and to the same dimensions as an existing structure.
    • For SB 9 projects, side and rear setbacks may not exceed four feet; a local agency may apply a lesser setback, such as 0–4 feet.
    • The local agency cannot apply existing side and rear setbacks applicable in the single-family residential zones.
    • The four-foot side and rear setback standards are not subject to modification.
    • The fact sheet cites Government Code Sections 65852.21(b)(2)(B) and 66411.7(c)(3).

    maximum side setback: <= 4 feet (A local agency may choose to apply a lesser setback, including 0–4 feet.) · maximum rear setback: <= 4 feet (A local agency may choose to apply a lesser setback, including 0–4 feet.)

    “SB 9 establishes an across-the-board maximum four-foot side and rear setbacks.”
    One more reviewed finding on this topic
    • District specific (with conditions) — Building setbacks, side and rear yard requirements, and property line requirements under California's State Housing Law framework.
      “building setback, side and rear yard requirements, and property line requirements are hereby specifically and entirely reserved to the local jurisdictions”
  • Living in an RVTemporary only (with conditions)

    Occupancy of recreational vehicles as residential units in California.

    • RVs are not intended for occupancy as permanent dwellings.
    • Unless a local ordinance allows otherwise, RV occupancy generally is limited to mobilehome parks or special occupancy parks governed by the Mobilehome Parks Act or Special Occupancy Parks Act.
    • Applicable state or local approval and enforcement requirements depend on the RV's location and classification.

    maximum gross area: <= 400 square feet (Measured at maximum horizontal projections; internal living room area must be less than 320 square feet excluding specified built-in equipment and bath/toilet rooms.)

    “RVs are not intended for occupancy as a permanent dwelling. [...] Unless otherwise allowed by a local ordinance, RVs generally may be occupied only in mobilehome parks or special occupancy parks”
  • Camping on your landLimited

    Camping in units operated by the California Department of Parks and Recreation statewide.

    • Camping is confined to areas designated for that purpose.
    • Occupancy by the same persons, equipment, or vehicles is generally limited to 30 days in any calendar year in that unit.
    • The Department may establish shorter or longer occupancy limits.
    • When a shorter seasonal limit applies, the camper must vacate the campsite and may not reregister in the unit until 48 hours have expired, measured from 12:00 noon on the checkout day to 12:00 noon on the second day following.
    • A district superintendent may permit one-night camping in a day-use area or portion of one, subject to Department-established fees and vehicle limitations; occupants must vacate by 9:00 a.m. the following morning.
    • California State Parks' current reservation policy states that each campground has a consecutive-night limit, requires a 48-hour absence after that limit, and generally has a 30-night annual maximum, subject to individual park policies.

    general annual occupancy limit: 30 days per calendar year per unit (The Department may establish shorter or longer limits of occupancy.) · return interval after shorter seasonal limit: 48 hours (Measured from 12:00 noon of the checkout day to 12:00 noon of the second day following.) · one-night camping in day-use area: 1 night (Only if permitted by the district superintendent; occupants must vacate by 9:00 a.m. the following morning.)

    “Occupancy by the same persons, equipment, or vehicles of any camping facility is limited to a total of 30 days in any calendar year in that unit.”
    One more reviewed finding on this topic
    • Allowed (with conditions) — Temporary camping in California special occupancy parks, including parks containing recreational vehicles, tents, or camping cabins.
      ““Special occupancy park” means a recreational vehicle park, temporary recreational vehicle park, incidental camping area, or tent camp.”
  • Manufactured homesAllowed (with conditions)

    Occupancy of manufactured homes inside or outside mobilehome parks in California.

    • The manufactured home must satisfy applicable federal standards and California Manufactured Housing Act and Title 25 requirements.
    • Installation and approval for occupancy are governed by the Mobilehome Parks Act.
    • HCD or a local enforcement agency with assumed Mobilehome Parks Act authority is responsible for ensuring compliance with statutory construction and maintenance requirements.
    • Local agency approvals may be necessary for the project.

    minimum width for a new manufactured home: >= 8 body feet (The statutory definition also includes units at least 40 body feet in length.) · minimum erected floor area for a new manufactured home: >= 320 square feet

    “MHs may be occupied outside or inside of mobilehome parks and installation and approval for occupancy is governed by the Mobilehome Parks Act (MPA), HSC Sections 18200, et seq., and Title 25, CCR Sections 1000, et seq.”
  • Accessory dwellingsAllowed (with conditions)

    ADUs and junior ADUs subject to California State ADU Law.

    • Approval is ministerial and without discretionary review or a hearing.
    • Development standards must be objective and knowable in advance.
    • The local permitting agency must determine application completeness and provide written notice within 15 business days.
    • If an application is incomplete, the agency must identify missing items and explain how to complete it.
    • Local site, building, health, safety, fire, utility, and other applicable requirements continue to apply.

    written completeness determination: <= 15 business days (Measured from the permitting agency's receipt of the application.) · final written determination after appeal: <= 60 business days (Applies after receipt of the written appeal.)

    “A permit application for an accessory dwelling unit shall be considered and approved ministerially without discretionary review or a hearing [...] A permitting agency shall determine whether an application to create or serve an accessory dwelling unit is complete and provide written notice of this determination to the applicant not later than 15 business days after the permitting agency received the application.”
  • Mandatory utility hookupSewer (with conditions)

    Certain existing OWTS in California Tier 3 impaired-water-body areas that commit to connect to a centralized wastewater collection and treatment system regulated through waste discharge requirements.

    • The OWTS must have been constructed and operating, or permitted, on or before the date the nearby water body was added to OWTS Policy Attachment 2.
    • The owner must commit by legally binding document to connect to a centralized wastewater collection and treatment system regulated through waste discharge requirements.
    • The owner must sign the legally binding document within 48 months after the nearby water body's initial listing on Attachment 2.
    • The specified connection date may not extend beyond nine years after the date the nearby water body is added to Attachment 2.
    • The rule is an exception to Section 10 requirements for qualifying existing or permitted systems; it is not a general statewide requirement that every property connect to public sewer.

    deadline to sign connection commitment: 48 months (Measured from the date the nearby water body is initially listed on Attachment 2.) · maximum time to complete connection: <= 9 years (Measured from the date the nearby water body is added to Attachment 2.)

    “The owner must sign the document within forty-eight months of the date that the nearby water body is initially listed on Attachment 2. The specified date for the connection to the centralized community wastewater collection and treatment system shall not extend beyond nine years following the date that the nearby water body is added to Attachment 2.”
  • Subdividing landRegulated (with conditions)

    Division of land in California that falls within the statutory definition of subdivision, including division for sale, lease, or financing.

    • A parcel map is generally required unless a final or parcel map is otherwise required or the preparation is waived by local ordinance.
    • Local ordinances may require a tentative map and may establish additional area, improvement, design, drainage, road, sanitary-disposal, water-supply, environmental-protection, and related requirements.
    • Certain railroad-right-of-way and governmental or public-utility conveyances are excepted from the parcel-map requirement described in Government Code section 66428(a).
    “A parcel map shall be required for subdivisions as to which a final or parcel map is not otherwise required by this chapter, unless the preparation of the parcel map is waived by local ordinance as provided in this section.”
  • Permit processPublished (with conditions)

    Construction, alteration, repair, movement, improvement, removal, conversion, or demolition of a building or structure in California.

    • A separate permit for each building or structure must be obtained from the building official before the work.
    • Code requirements vary by city and county; the applicable local building department must be consulted.
    “no building or structure may be erected, constructed, enlarged, altered, repaired, moved, improved, removed, converted or demolished unless a separate permit [...] has first been obtained”
  • Campground & park staysLimited

    Occupancy and use of manufactured homes and mobilehomes in California mobilehome parks and other locations subject to HCD jurisdiction.

    • HCD administers titling and registration for manufactured homes and mobilehomes.
    • HCD-inspected mobilehome parks are subject to health and safety enforcement where local government has not assumed enforcement.
    • Manufactured/mobilehome park regulations address construction, use, maintenance, and occupancy.
    • Separate local land-use, building, fire, health, and utility requirements may apply.
    “MHs may be occupied outside or inside of mobilehome parks and installation and approval for occupancy is governed by the Mobilehome Parks Act (MPA), HSC Sections 18200, et seq., and Title 25, CCR Sections 1000, et seq.”
    2 more reviewed findings on this topic
    • Limited — RV and trailer camping at Silver Strand State Beach Campground in the San Diego Coast District.
      “Camping Stay Limits: Applies to persons, equipment, or vehicles and any combination thereof [...] Maximum stay of 30 days per calendar year [...] Maximum 7 consecutive days during peak season (May 15 – September 15) [...] Maximum 14 consecutive days during non-peak season”
    • Limited — Occupancy and use of recreational vehicles in California special occupancy parks and designated RV sections of mobilehome parks.
      “Unless otherwise allowed by a local ordinance, RVs generally may be occupied only in mobilehome parks or special occupancy parks governed by the Mobilehome Parks Act”
  • county zoning authorityGeneral

    California county legislative bodies' authority to adopt zoning ordinances regulating buildings, structures, land uses, lots, yards, open space, lot coverage, intensity of use, parking, loading, and setbacks within county jurisdiction, including unincorporated areas.

    • The authority is exercised pursuant to Government Code Chapter 4, Zoning Regulations.
    • The statute separately authorizes city legislative bodies; incorporated municipalities may exercise their own zoning authority.
    • Government Code Section 65850 also lists authority to regulate signs and billboards, building and structure location, height, bulk, number of stories, and size, lot and open-space size and use, lot coverage, intensity of land use, offstreet parking and loading, and building setback lines.
    • The cited section states it was amended by Stats. 2017, Ch. 376, Sec. 1, effective January 1, 2018.
    “The legislative body of any county or city may, pursuant to this chapter, adopt ordinances that do any of the following:”
  • county building authorityGeneral

    California counties administering and enforcing state building standards through county building departments, including residential construction in unincorporated areas.

    • Each county must maintain building standards and state building regulations in the office of the building official responsible for administration and enforcement of state building standards.
    • The statewide Title 24 standards apply subject to statutory exceptions and any authorized local amendments or local requirements.
    • The cited HCD bulletin concerns the 2019 California Building Standards Code and its July 1, 2021 supplement; later code editions may supersede those particular edition dates.
    “These codes shall be maintained in the office of the building official responsible for the administration and enforcement of state building standards”

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.

Living off-grid in San Mateo County, California

Is San Mateo County a good place to live off-grid or homestead?

San Mateo County scores 35/100 on the Bolthole Index, a marginal county profile. Its strengths: workable self-sufficiency basics (28.7″/yr rainfall). Watch-outs: about 722,806 people within 15 miles and elevated current hazard exposure.

Do you need a building permit in San Mateo County, California?

San Mateo County generally requires a residential building permit, and it enforces county zoning. Onsite septic is permitted by San Mateo County Environmental Health Services. Owner-builders may act as their own contractor to build their home. These answers are quoted from official sources and independently re-checked. Rules change and cities within the county differ — always confirm with the county before you buy or build.

Can you live in an RV or tiny home on your land in San Mateo County?

Living in an RV on your own land in San Mateo County is allowed on a temporary basis only: Statewide rule. Occupancy of recreational vehicles as residential units in California. RVs are not intended for occupancy as permanent dwellings. Unless a local ordinance allows otherwise, RV occupancy generally is limited to mobilehome parks or special occupancy parks governed by the Mobilehome Parks Act or Special Occupancy Parks Act. A tiny home is limited to specific cases. Confirm with the county before relying on it.

How much does land cost in San Mateo County, California?

Land in San Mateo County runs about $12,311 per acre, based on the latest county data.

What is the water situation in San Mateo County?

San Mateo County gets about 28.7" of rain a year, with severe drought in roughly 31.9% of years.

How remote is San Mateo County?

A typical private-land location has about 722,806 people within 15 miles and 9,988,219 within 100 miles. These radius catchments are the published fallback where road routing is unavailable.

Off-grid gear

Going off-grid in San Mateo County means bringing your own water and power. The kit we’d start with:

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How San Mateo compares in California

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