Portola Valley — Land Use

Last reviewed: July 2, 2026

Overview

Portola Valley's land-use rules relevant to zoning are codified in the town's zoning chapters (Chapters in the 18 range). The code organizes permitted principal uses, conditional uses, and accessory uses by district and ties dimensional standards to tables and combining districts. This page summarizes the use rules district‑by‑district, highlights the decision‑relevant numeric limits where the ordinance provides them, and points to the code sections you must check for parcel‑specific questions. See the town's rules on design review and development standards for related procedural and dimensional detail: Portola Valley Design Review and Portola Valley Development Standards.

How the code treats uses (baseline rules)

• A use is permitted only where the district regulations list it as a principal use, conditional use, or permitted accessory use; otherwise it is prohibited unless authorized through the procedures in the code (§ 18.02.100, § 18.02.110, § 18.02.120) .
• Conditional uses require a conditional use permit under Chapter 18.72 (§ 18.02.100) .
• Dimensional standards (setbacks, lot size, coverage, impervious limits) are established in the development standards tables and combining districts (see § 18.48.010, Chapter 18.50, § 18.52.010) . Refer to the town's parking rules separately at Portola Valley Parking.

District-by-district breakdown

Each subsection below states the district purpose, typical permitted uses (principal and conditional as summarized in the code), and where numeric development limits are set. For parcel‑ or project‑specific numbers (setbacks, minimum parcel area, slope density), the ordinance points you to tables and combining districts — see the citations.

O-A (Open Area)

• Purpose: Preserve open quality and scenic/natural characteristics in visually important sites (§ 18.26.010) .
• Typical principal (permitted) uses: those listed in § 18.26.020, which include general uses from § 18.36.010, agricultural uses, public parks/open space, and certain temporary uses (§ 18.26.020) .
• Conditional uses: listed in § 18.26.030, including larger agricultural buildings (barns), private/commercial recreation, residential planned unit development (PUD) where the O‑A is associated with residential/combing districts, and employee housing for qualified agricultural uses (§ 18.26.030) .
• Dimensional/other controls: accessory use rules (Chapter 18.42), parcel area and bulk requirements (Chapters 18.48–18.60), off‑street parking (Chapter 18.60), required conditions in § 18.26.050, and any special setback lines in Chapter 18.58 (§ 18.26.010) . Use the overlay mapping/combining districts to confirm allowed residential density in any given O‑A location.

R-E (Residential Estate)

• Purpose: Maintain a rural environment with larger parcels appropriate for single‑family dwellings and accessory equestrian uses (§ 18.12.010) .
• Principal permitted uses: single‑family dwellings (including small residential care/supportive/transitional housing), public buildings when conforming to the general plan, and the base list in § 18.36.010 (§ 18.12.020) .
• Conditional uses: crop/tree farming, nurseries (no retail), religious institutions and private schools on arterials, boarding stables and day care centers, wineries (with site and production limits), employee housing for agricultural uses, and PUDs as listed in § 18.12.030 (§ 18.12.030) .
• Accessory uses: equestrian facilities serving a single dwelling (subject to stable ordinance requirements), room rentals limited to incidental hosting of a single paying guest, and other accessory uses in Chapters 18.36 and 18.40 (§ 18.12.040) .
• Dimensional standards: parcel area, open area, and bulk are controlled by Chapters 18.42 and 18.48–18.60; some PUD flexibility exists (e.g., planning commission may authorize reduced net area per lot in certain cases) (§ 18.12.010, § 18.50.050) .

R-1 (Single‑Family Residential)

• Purpose: Support single‑family rural‑urban living with lot sizes to preserve open space and privacy (§ 18.14.010) .
• Principal permitted uses: single‑family dwellings (including certain group homes and small residential care/supportive/transitional housing) and the base list in § 18.36.010 (§ 18.14.020) .
• Conditional uses: listed in § 18.14.030 (see code for full conditional list) and subject to the conditional use permit process (§ 18.02.100) .
• Dimensional standards: required yards and minimum parcel areas are set in Tables 1 and 2 of § 18.48.010 and the yard rules in § 18.52.010; planned unit developments and slope density combining districts may change unit counts (§ 18.48.010, § 18.52.010, Chapter 18.50) .

M‑U (Mixed‑Use) — e.g., M‑U1, M‑U2

• Purpose: Mixed residential and non‑residential development at defined densities and FAR; the code sets a specific development standards table for these districts (§ 18.23.050) .
• Key decision‑relevant numeric standards (excerpted from Table 18.23.050; see the code table for full detail):

• Notes: The table explicitly references supportive housing overlay modifications for specific Alpine Road properties; always check overlay provisions (see Portola Valley Overlay Districts) and the full table in § 18.23.050 for parcel‑level modifications .

P‑C (Planned Community)

• Purpose and scope: P‑C districts are intended for unified development of large tracts with residences and supporting local facilities (parks, trails, schools). P‑C district establishment and build‑out are governed by a general development plan for each P‑C district (§ 18.28.050–18.28.080) .
• Permitted uses: can include principal and accessory uses from R‑1 and R‑E (if included in the approved general development plan) and horticulture/grazing; additional uses may be allowed by conditional use in the approved plan (§ 18.28.060) .
• Conditions: P‑C districts may only be established on large parcels (e.g., 60+ acres per § 18.28.070), require a single ownership or joint application, and must include an S‑D (combining) district that sets density (§ 18.28.070–18.28.080) .

Cross‑cutting programmatic rules you must check

• Uses not listed are prohibited unless authorized by the code process (§ 18.02.120) .
• Accessory uses and ADU treatment: accessory uses are defined at § 18.02.110 and the code separately addresses accessory structures and ADUs — consult the town ADU guidance at Portola Valley ADUs and the code chapters referenced in the definitions (§ 18.04.030, § 18.04.151) .
• Parking requirements are in Chapter 18.60; see the town's parking summary at Portola Valley Parking for typical ratios and what the code requires in different districts (§ 18.26.010, § 18.12.010, etc., reference Chapter 18.60) .
• Design and site/architectural review: some use and building changes trigger architectural and site plan review (referral to Architectural & Site Control Commission) — see § 18.62.040 and Chapter 18.64 and the town's design review page Portola Valley Design Review .
• Special setbacks, frontages along scenic corridors (e.g., Alpine Road), slope density combining districts (S‑D), and impervious surface limits can materially change what you can build (§ 18.58, Chapter 18.50, § 18.56.010–011) .

Checklist

• Confirm the property's zoning district on the town zoning map and identify any overlay/combining districts (S‑D, Supportive Housing Overlay) and special setback lines (Chapter 18.58) — verify with the jurisdiction.
• Determine whether the proposed use is listed as a principal, conditional, or accessory use in the applicable district (§ 18.02.100–120) .
• If conditional, prepare a Conditional Use Permit application consistent with Chapter 18.72 and the district's conditional use list (e.g., § 18.12.030, § 18.26.030) .
• Pull dimensional standards: required lot area, setbacks, height, coverage, FAR from § 18.48.010, Table 18.23.050 (for M‑U), and Chapter 18.50 for slope/combining district calculations (§ 18.48.010, § 18.23.050, Chapter 18.50) .
• Prepare site plan, parking calculations (Chapter 18.60), and any landscape/impervious surface calculations (Chapters 18.56, 18.48) and submit per the zoning permit rules (§ 18.62.020–040) .
• Check for design review triggers; if required, follow procedures in Chapter 18.64 and the town's design review guidance Portola Valley Design Review (§ 18.62.040) .
• For ADUs, consult the town ADU guidance and State ADU law links: Portola Valley ADUs and California ADU law.

Risks & Ambiguities

Plain‑English summary

Portola Valley’s zoning code organizes what you can and cannot do by district: each district (for example R‑1, R‑E, O‑A, M‑U, P‑C) lists permitted principal uses, conditional uses (which need a CUP), and accessory uses; dimensional limits are found in development tables and overlays that can change parcel‑specific rules (§ 18.02.100–120, § 18.48.010, § 18.23.050) .

Source References

• Portola Valley Zoning Code: Definitions and Use categories — § 18.02.100–120 (conditional, accessory, uses not listed) .
• R‑E district use list and conditional uses — § 18.12.010–040 .
• R‑1 district use list — § 18.14.010–020 .
• O‑A district purpose, principal and conditional uses — § 18.26.010–030 .
• P‑C (Planned Community) permitted uses and conditions — § 18.28.050–080 .
• Mixed‑use development standards (Table 18.23.050) — § 18.23.050 (development standards table, incl. density, FAR, setbacks) .
• Planned unit development & slope density combining districts — Chapter 18.50 (incl. § 18.50.050, § 18.50.060) .
• Yards and measurement rules — § 18.52.010 and Table references in § 18.48.010 (Tables 1 & 2) .
• Impervious surface & landscaping limits — Chapter 18.56 (§ 18.56.010–011) .
• Cannabis rules (personal vs. commercial, limits) — Chapter 18.39 (§ 18.39.030–060) .
• Zoning permit procedures and referral to architectural/site review — § 18.62.020–040 and § 18.62.040 referring to Chapter 18.64 .

If you need the exact text for any of the above sections or the full numeric tables for a parcel, request the specific § or the parcel APN and I will extract the exact code lines and table rows for you. Where the code points to other chapters (e.g., special setback lines in Chapter 18.58, stable ordinance Chapter 6.12), those texts were referenced in the code snippets and should be read for parcel decisions; if you want I can pull those excerpts next.

Retrieved passages

• Portola Valley Zoning Code (Section 18.54.050.) High relevance show source text
• Portola Valley Zoning Code (§ 1) High relevance show source text
• Portola Valley Zoning Code (§ 4) High relevance show source text
• Portola Valley Zoning Code (§ 3) High relevance show source text
• Portola Valley Zoning Code (title could) High relevance show source text
• Portola Valley Zoning Code (§ 1) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.72.) High relevance show source text
• Portola Valley Zoning Code (§ 1) Medium relevance show source text

Cited sections

• Portola Valley Zoning Code: Definitions and Use categories — § **18.02.100–120** (conditional, accessory, uses not listed) .
• R‑E district use list and conditional uses — § **18.12.010–040** .
• R‑1 district use list — § **18.14.010–020** .
• O‑A district purpose, principal and conditional uses — § **18.26.010–030** .
• P‑C (Planned Community) permitted uses and conditions — § **18.28.050–080** .
• Mixed‑use development standards (Table **18.23.050**) — § **18.23.050** (development standards table, incl. density, FAR, setbacks) .
• Planned unit development & slope density combining districts — Chapter **18.50** (incl. § **18.50.050**, § **18.50.060**) .
• Yards and measurement rules — § **18.52.010** and Table references in § **18.48.010** (Tables 1 & 2) .
• Impervious surface & landscaping limits — Chapter **18.56** (§ **18.56.010–011**) .
• Cannabis rules (personal vs. commercial, limits) — Chapter **18.39** (§ **18.39.030–060**) .
• Zoning permit procedures and referral to architectural/site review — § **18.62.020–040** and § **18.62.040** referring to Chapter **18.64** .
• PortolaValley_ZoningCode.md

• Official Portola Valley code library