Portola Valley Zoning, Planning & Building Codes

Last reviewed: July 3, 2026

Overview

This page orients you to the Town of Portola Valley’s local zoning and planning framework as codified in the town municipal code (the zoning ordinance uses sections numbered in the 18.x series). The code establishes the town’s district map, combining/overlay districts, objective and discretionary development standards (setbacks, height, lot coverage, FAR where used), design-review processes, special chapters implementing state housing laws (ADUs and SB 9), and the permit paths (zoning permits, building permits, certificates of occupancy). The most relevant local provisions appear in chapters such as § 18.06.010, § 18.52.010, § 18.64.050, § 18.27.010, and the ADU rules collected in the accessory-dwelling provisions.

Note: this summary synthesizes the town code text fragments that were provided; readers should confirm with the town’s official code or staff for final, project‑level requirements.

How Portola Valley's code is organized

• The zoning rules are codified in town code sections using the 18.x numbering (the zoning map and district rules are introduced in § 18.06.010 and related sections). § 18.06.010 lists the principal zoning districts while § 18.06.020 establishes combining (overlay) districts such as density/acreage combiners and design-related overlays.

• Definitions live in Chapter 18.04 (useful for terms like “ADU,” “JADU,” “AMFA,” and “multifamily structure”) and the map is adopted by § 18.08.010. See the code’s definitions and map interpretation rules in § 18.04.010–§ 18.08.020.

• Procedural and review chapters: zoning permits and zoning-permit procedures are in § 18.62.010–§ 18.62.060 (application, issuance, appeals), while design and architectural/site review is in Chapter 18.64 (see § 18.64.045–§ 18.64.060). Conditional uses and appeals reference Chapters 18.72, 18.66, and 18.70 as appropriate.

• Special-topic chapters: floodplain rules appear in Chapter 18.32, planned‑unit development in Chapter 18.50, special setback lines in Chapter 18.58, and the SB 9 implementation rules in Chapter 18.27. ADU/JADU standards are in the ADU provisions within the code (definitions in Chapter 18.04 and ADU standards in the ADU chapter excerpts).

Inline links for quick navigation: the town’s subject pages for zoning, the town’s development standards and the town’s permitting/review topics are summarized on GoCodebook — see Portola Valley’s pages for Zoning, Development Standards, Parking, Design Review, Overlay Districts, ADUs, and the California Building Standards Code.

Zoning district families

Portola Valley’s base districts are explicitly enumerated in § 18.06.010; the code distinguishes several district “families” (bold below for quick scanning) and uses combining districts/overlays to refine density, design, hazards and other constraints:

• Residential districts: R-E (Residential Estate), R-1 (Single‑family residential), R-MF (Multi‑family residential), M-R (Mountainous residential). § 18.06.010 enumerates these base residential districts and Chapter 18.10 describes residential purposes and objectives.

• Commercial / professional / mixed-use: C-C (Community Commercial), A-P (Administrative‑Professional), and the M-U / MU (Mixed‑Use) district; the M‑U table (Table 18.23.050) gives district-specific density, FAR, height and setback rules for mixed-use parcels.

• Special and open districts: O-A (Open Area), P‑C (Planned Community), plus specialized combining districts such as D‑R (Design Review), F‑P (Floodplain) and S‑D (Slope Density). These combining/overlay districts are set out in § 18.06.020 and the special‑district chapters (e.g., Chapter 18.26 for O‑A).

• Historic and housing overlays: the code includes an H‑R (Historic Resource) combining district (Chapter 18.31) and recently references a Supportive Housing Overlay for specific Alpine Road parcels (noted in Table 18.23.050 and connected to the 2023–2031 Housing Element).

Practical note: base district rules set general permissions and density; the combining districts and P‑C or planned‑unit regimes frequently change allowed unit counts, setbacks or building‑envelope rules on a parcel‑by‑parcel basis (e.g., S‑D/slope density and P‑C rules). See § 18.28.080–.100 and § 18.50.050 for how dwelling counts/area are computed in special districts.

Citywide development standards

At a town‑wide level, Portola Valley’s code sets standards in multiple chapters; below are the orientation points and where to find the controlling rules.

• Setbacks and yards: required yard dimensions and measurement rules are in § 18.52.010 (defines front/side/rear yard measurement and exceptions) and special setback lines (scenic or corridor setbacks) are in Chapter 18.58 (for example, Skyline Blvd and Alpine Road special lines). Use the town’s Development Standards page for a practical view of these rules. § 18.52.010 and § 18.58.020 explain measurement and special setbacks.

• Height: building height rules and exceptions are in Chapter 18.54 (height measurement rules, exceptions and limits; e.g., exceptions for chimneys, towers, or PUD approvals). See § 18.54.030 for exceptions and related measurement provisions.

• Coverages / FAR / AMFA: floor area and lot‑coverage rules (including Portola Valley’s parcel‑specific Adjusted Maximum Floor Area or AMFA) are addressed in the definitions chapter and in Chapter 18.54 and in specialized tables (Table 18.23.050 for the M‑U district). The code defines AMFA as a parcel‑specific floor‑area cap that accounts for slope, ground‑movement potential and flooding maps. See the AMFA discussion in the SB 9 and ADU contexts for application.

• Parking: off‑street parking standards are in Chapter 18.60 (planning, dimensions and access). Planned unit developments and P‑C approvals reference § 18.60.110 for visitor/garage parking requirements. For a user‑friendly summary of how parking applies to small projects, see the town’s Parking page.

• Landscaping, screening, and lighting: the code requires landscape and screening buffers in many districts (see Table 18.23.050 for LAR/IAR in the M‑U district and Chapter 18.36 for utilities/lighting/landscape provisions). Also see the town’s Landscaping and Screening resource for practical rules.

• Fire / safety / ground movement constraints: development on parcels with mapped ground‑movement potential, floodplains, and wildfire concerns is constrained by specific chapters (e.g., Chapter 18.32 for floodplain; PUD and planned‑community rules limit units on high‑risk ground in § 18.50.060). SB 9 and ADU provisions also include fire‑safety checklists and home‑hardening requirements.

Design / discretionary review

• Two review tracks coexist: objective/ministerial review and discretionary/design review. The Architectural and Site Control Commission (ASCC) and staff reviews both apply depending on project type. Design‑guideline use and ASCC procedures are set out in Chapter 18.64 (see § 18.64.045–.050 for the design principles and guidelines). The code instructs the ASCC to apply design principles that preserve Portola Valley’s rural character.

• Many smaller, state‑mandated projects (ADUs that meet the state objective standards, SB 9 units that meet the town’s objective checklist) are processed ministerially (no discretionary hearing). Where the town retains discretionary review, it is governed by the standards in Chapter 18.64 and by the findings listed for discretionary approvals (see the ADU ministerial/discretionary split in the ADU chapter).

• Practical orientation: expect the ASCC on projects that propose visible exterior changes, new detached structures in sensitive corridors, or projects that request exceptions to special setbacks. The ASCC may require story poles, site staking, or landscape buffers before hearings. See § 18.64.045 for the ASCC’s principles and review tools.

Specific plans & overlays

• Portola Valley uses combining districts and special chapters to overlay additional rules on base districts: examples include the F‑P (Floodplain) combining district (Chapter 18.32), H‑R (Historic Resource) combining district (Chapter 18.31), S‑D (Slope Density) combining districts, and special setback lines (Chapter 18.58). The combining districts are listed in § 18.06.020.

• The code also integrates specific-area rules: the M‑U (Mixed‑Use) district’s Table 18.23.050 contains parcel‑specific notes tied to the Town’s 2023–2031 Housing Element (e.g., Supportive Housing Overlay standards for Alpine Road parcels). Those special standards modify FAR, CAR and other metrics for identified sites.

• Where parcels are in P‑C or planned developments, the general development plan and associated S‑D combining districts control unit counts, spacing and open space; see § 18.28.080–.100 and § 18.50.050 for P‑C and PUD rules.

For a quick tour of the overlays and historic rules, see the town’s Overlay Districts and Historic Preservation pages.

Building permits & review (practical permit path)

• Zoning permit is the first step for most changes in land use or structure. The code states “no structure shall be erected or structurally altered, nor shall the use of any land or structure be changed until a zoning permit has been issued by the town planner” and no building shall be occupied until a certificate of occupancy (if required) is issued — see § 18.62.010–§ 18.62.060 for the zoning‑permit application, investigation, issuance, fee and appeals process.

• Design/architectural review: where architectural and site plan review is required, the application is referred to the ASCC per § 18.62.040 and Chapter 18.64 sets the review criteria and possible requests for site demonstrations (story poles, staking).

• Conditional uses / variances / appeals: conditional uses require permits under § 18.02.100 and Chapter 18.72; appeals and the board of adjustment process reference Chapters 18.66 and 18.70 as appeal paths from staff denials.

• Ministerial vs. discretionary: many ADUs and SB 9 ministerial‑eligible projects are reviewed without public hearings (ministerial review by the planning & building director), provided they meet objective standards in the code (see the ADU ministerial rules and SB 9 objective checklist provisions). When an application is ministerial the director must approve if objective requirements are met; discretionary review applies if deviations or discretionary findings are required. See § 18.27.080 (SB 9 permit review process) and the ADU ministerial-review descriptions.

• Practical sequence: (1) pre‑application / inquiry to planning and building; (2) zoning permit and application checklist per § 18.62.020; (3) referrals to ASCC or P&Z when required; (4) building permit submittal and concurrent code compliance checks (structural, fire, septic/sewer); (5) final inspections and certificate of occupancy.

State housing law in Portola Valley

Portola Valley’s local code integrates state housing law in several explicit ways. Below is a short, practical synthesis with the controlling local code references.

ADUs & JADUs (local rules that implement state law)

• Portola Valley permits ADUs and JADUs consistent with state law but adds local procedural standards. The code allows one ADU and one JADU on parcels under 3.5 acres and up to two ADUs on larger parcels (with one detached and one internal) — see the ADU number limits and the state‑exemption language in the ADU chapter. The code explicitly adopts the state exemption that certain ADUs are ministerial and not subject to many local lot‑coverage/AMFA/size/setback limits (subject to specific safety exceptions). See the ADU provisions for floor‑area maxima (e.g., 800–1,500 sq ft ranges depending on setbacks and parcel size) and internal ADU conversion rules. § 18.04.152, the ADU chapter sections, and the ADU ministerial/discretionary provisions are the controlling code excerpts.

• ADU parking and driveway rules: internal ADUs and JADUs may not require dedicated parking; external ADUs typically require one dedicated parking space unless waived under the code’s exceptions (see the ADU parking rules and § 18.60.020 for dimensions). ADU utilities/undergrounding, fire‑sprinkler and building‑code compliance are addressed in the ADU chapter.

• For practical detail and state‑law crosswalk, Portola Valley’s ADU rules explicitly reference compliance with the California Building Code and state ADU statutes; see the local ADU definitions and building‑code references in the ADU chapter and Chapter 18.04. See the town’s ADU page for step‑by‑step ministerial pathways.

(See also the statewide summary of ADU law and the California Building Standards Code on the GoCodebook state pages: California ADU law and California Building Standards Code.)

SB 9 (ministerial duplex/lot split law)

• Portola Valley implements SB 9 in Chapter 18.27. The chapter establishes objective standards for SB 9 residential development (eligibility tied to Chapter 17.13 lot‑split rules), sets AMFA rules for resulting parcels, defines setbacks, minimum side/rear setbacks of 4 ft for SB 9 units (with special additional restrictions when local setbacks are not met), height limits (e.g., 16–24 ft caps depending on setback compliance), and ministerial review procedures. The code requires the town to process SB 9 applications ministerially and to notify owners within 300 feet when an application is filed. See § 18.27.010–§ 18.27.080 for full details.

Density bonus, rent rules, and rent control

• Portola Valley code chapters excerpted in the retrieved materials discuss affordable/supportive housing overlays and the town’s housing element site designations, but the sample files do not include a local rent‑control ordinance or a local density‑bonus implementation chapter text in the retrieved excerpts. Verify local density‑bonus implementation and rent‑control status with Planning staff or the full municipal code (not found in the retrieved materials). Not found in retrieved materials — verify with the jurisdiction.

Information gaps / what to verify with the town

• The retrieved excerpts give a deep view of many chapters (ADU chapter, SB 9 chapter, district lists, setbacks, ASCC design standards, PUD rules). However, the full code text, the zoning map, fee schedules, and any recent ordinances beyond the provided excerpts should be confirmed with the official municipal code or the Portola Valley Planning & Building Department. Where I note “not found in retrieved materials,” please check the town’s online municipal code or contact staff for the latest ordinance and fee schedule.

Source References

• Portola Valley Municipal Code — Districts established § 18.06.010
• Combining/overlay districts § 18.06.020 (list of combining districts)
• Yards / setback measurement § 18.52.010
• Special setback lines (Skyline, Alpine, Portola Rd) § 18.58.020
• Design review principles and guidelines § 18.64.045–.050
• Zoning permit procedure and issuance § 18.62.010–.060
• Mixed‑use development standards (Table 18.23.050) — M‑U district standards (setbacks, FAR, height) § 18.23.050
• ADU / JADU local standards, sizing, parking & ministerial/discretionary rules (ADU chapter excerpts) (ADU provisions; see ADU text and definitions in Chapters 18.04 and ADU chapter excerpts)
• SB 9 implementation chapter (standards and ministerial review) § 18.27.010–.080
• Planned unit development / P‑C rules and dwelling‑count computation § 18.50.050–.060