Building permits, zoning and septic in Santa Clara County, California

Yes: a building permit is required before you construct, enlarge, alter, move, replace, repair, improve, convert, demolish or change the occupancy of a building or structure in unincorporated Santa Clara County¹. A short list of small projects is exempt -- a one-story detached accessory structure up to 120 square feet, a fence up to 7 feet high, and a retaining wall up to 4 feet high measured from the footing -- but any retaining wall that supports a surcharge like a road, structure or hillside needs a permit regardless of height¹. All work performed under a county building or development permit must be inspected and approved, and it cannot be covered before a County Building Inspector approves it¹¹. An inspection must be approved within 12 months of permit issuance or a new permit is required; after an approved inspection, a 6-month gap without another approval requires a Permit to Complete¹². The county enforces the 2025 California building codes and the 2024 International Property Maintenance Code, with local amendments¹. A conditional exemption covers qualifying agricultural buildings under 10,000 square feet on a single parcel of at least 10 acres outside a FEMA Special Flood Hazard Area; it does not exempt grading, electrical or plumbing permits, and the application requires prior septic clearance from Environmental Health¹⁰.

Santa Clara County's Department of Planning and Development handles building permits for unincorporated land from 70 West Hedding Street, East Wing, 7th Floor, San Jose, CA 95110, at (408) 299-5700¹. Confirm jurisdiction and zoning before applying; a planning application may be required first¹. Municipal building-permit requirements are separate in Mountain View¹³, Milpitas¹⁴, Gilroy¹⁵, Campbell¹⁶, Town of Los Altos Hills¹⁷. Santa Clara County Department of Environmental Health separately handles OWTS permits where sewer is unavailable³. Gilroy requires written Health Officer approval before issuing a building permit for a building without public sewer¹⁵. Apply through the county Public Permit Portal; normal processing takes 4–6 weeks, depending on workload and complexity¹. Fees depend on project size, type and valuation; plan-check and PO-review fees are due at submission, with remaining building-permit and applicable inspection, encroachment, geologic-review and septic-system fees due before issuance¹.

Unincorporated Santa Clara County follows the county General Plan, Ordinance Code and Zoning Ordinance; Property Explorer identifies parcel jurisdiction, zoning and site constraints^1,18. Base setbacks are 25 feet front/rear and 5 feet side in R1/R1E/R2/A1, and 30 feet on all sides in A/AR/HS/RR, subject to exceptions⁸. Combining districts can change setbacks, and accessory structures have separate standards⁹. Building lot coverage is capped at 50% in R3; the -n3 Stanford Upper San Juan district caps single-family coverage at 20% and two-family/multifamily coverage at 35%, with qualifying ADU exemptions⁷. The -cv Coyote Valley district caps coverage at 7,500 square feet per legal lot, exempting qualifying ADUs and agricultural uses ancillary to onsite agriculture⁷. Municipal zoning applies inside San Jose¹⁹, Sunnyvale²⁰, Mountain View²¹, Milpitas²², Gilroy²³, Morgan Hill²⁴, Campbell²⁵, Town of Los Gatos²⁶, Los Altos²⁷, Town of Los Altos Hills²⁸. Santa Clara County Environmental Health remains the OWTS authority where sewer is unavailable, including Los Gatos and Los Altos Hills^3,29,30.

Septic systems in Santa Clara County -- called onsite wastewater treatment systems, or OWTS -- are permitted by the County Department of Environmental Health, which issues permits for new systems and repairs and inspects installation³. An occupied building must connect to an approved available sanitary sewer when the property abuts a street or alley containing one or the property line is within 300 feet³¹. Where sewer is unavailable, an occupied building must have a water-flush toilet connected to an approved OWTS; a conventional system requires approved plans, site testing, a septic tank and dual subsurface dispersal fields³². Cesspools are prohibited in Santa Clara County³². For new development, Environmental Health clearance comes before building-permit issuance; the OWTS construction permit is issued with the building permit and must be obtained before OWTS work begins, with required inspections scheduled^4,33. Only about 1% of county land is rated free of severe limits for a conventional drain field, so investigate early³⁴.

RVs, campers, trailers, boats and similar vehicles may not ordinarily be used as housing on residential lots in unincorporated Santa Clara County⁶. Temporary occupancy during dwelling construction requires approval, a primary-residence building permit issued before or with that approval, and use of the new home's approved septic system unless sewer is available⁷. Unincorporated Santa Clara County allows ADUs on legal residential or mixed-use lots with an existing or proposed single-family residence, adequate water and sewage service, compliant setbacks and fire/life-safety standards; planning review and building permits apply, with provisions varying by district and lot size³⁵. A qualifying JADU must be within the residence and no larger than 500 square feet; owner-occupancy of the main home or JADU is required³⁵. A movable tiny home may replace a standard ADU, with DMV registration, required certification and direct water, wastewater and electric connections; waste holding tanks are prohibited⁷. The 100-square-foot enclosed-space minimum applies to movable tiny-home ADUs, not every dwelling type⁷. The primary residence needs building-site approval before the ADU application, and ADU rentals must last at least 30 days⁷. Ask Planning and Development about primary-residence tiny-home approval: California requires an approved classification and location^1,36.

1. Search Property Explorer by parcel number or address to confirm jurisdiction, site constraints and zoning¹⁸.
2. Confirm the intended use and lot meet the applicable zoning, minimum-lot and setback rules^1,7.
3. Determine wastewater service: connect to an approved available sewer when required, or obtain Environmental Health clearance before the building permit and the OWTS construction permit at building-permit issuance where sewer is unavailable^4,31.
4. Obtain a Valley Water permit before covered private-well work begins, if needed³⁷. Submit application materials and plans through the Public Permit Portal to the Department of Planning and Development¹.
5. If you act as owner-builder, sign the declaration and accept responsibility for permits, code compliance and inspections; the exemption is from contractor licensing only, with eligibility depending on who performs the work and whether the improvements are intended for sale^5,38.
6. Request each required inspection separately, do not cover work before approval, and obtain final inspections to close every related permit¹¹.

Start with jurisdiction: a parcel inside a city follows that city's planning rules, while unincorporated land follows Santa Clara County zoning². Lot creation and building-site minima differ: R1/R1E/R2/A1 generally require 5,000 square feet for lot creation versus 3,750 for a building site, subject to table notes and combining districts⁷. RS requires 5 acres for lot creation versus 1 acre for a building site; OS/F generally requires 160 acres for lot creation with clustering exceptions, and SCA uses a 20–160 acre slope-density formula without clustering or minimum-lot reductions⁷. If you plan to split land, expect a tentative map, improvement plans, access and utilities for each proposed parcel, with additional requirements possible based on location and site conditions³⁹. Check the county flood map because development in a mapped Special Flood Hazard Area can require a floodplain development permit⁴⁰. Confirm driveway feasibility; county guidance requires at least 10 feet of unobstructed width and at least 8 feet of surfacing, with greater width possible when the fire marshal requires it⁹. Investigate septic suitability early because only about 1% of county land is rated without severe limits for a conventional drain field³⁴. If the parcel needs a private well, obtain the required Valley Water permit before covered well work begins³⁷.