Portola Valley — Development Standards

Last reviewed: July 2, 2026

Overview

This page summarizes the Portola Valley Zoning Ordinance (Title 18) rules that control development setbacks, height, lot coverage/CAR, density, and FAR, and how those standards vary by district. It synthesizes the Town’s numeric standards and practical points you’ll need when planning a project in Portola Valley. Where the ordinance text was available in the uploaded materials I cite the controlling code § and the file excerpt; where our extract did not show a clear section number I note that and recommend verification with the Town.

(If you need the Town’s overall zoning map or overview first, see the Portola Valley zoning & planning overview.)

Key links (first natural mention of each)

• Portola Valley zoning & planning overview: Portola Valley zoning & planning overview
• For on-site vehicle requirements see Portola Valley parking.
• Design controls are reviewed under the Town’s design review processes.
• Special setbacks and corridor rules are in the Town’s overlay districts (Chapter 18.58).
• Accessory dwelling rules and limitations are summarized on the Portola Valley ADUs page — and state ADU law also applies; see California Building Standards Code and the state ADU law pages for statutory backstops.
• Landscaping and screening requirements are enforced per the Town’s landscaping and screening policies.
• If you expect to seek relief, consult the Town’s variances and exceptions rules.

District-by-district breakdown

Note: the ordinance organizes development standards into district tables. Below I cover the districts where the uploaded excerpts contain explicit development tables and numeric limits.

R-MF (Multi‑Family Residential) — R‑MF‑4 and R‑MF‑23

Purpose and where it applies

• The R‑MF districts regulate multi‑family housing at different densities; the ordinance distinguishes R‑MF‑4 (lower density) and R‑MF‑23 (higher density) and ties development standards to those sub-districts. See § 18.15.050 for the full table of standards.

Typical permitted uses

• Multi-family housing, accessory uses described in § 18.15.040, and accessory structures (subject to accessory rules). See § 18.15.040 and § 18.42.010.

Key dimensional standards (high‑decision items)

• Density: R‑MF‑4 Min 2 du/ac; Max 4 du/ac. R‑MF‑23 Min 20 du/ac; Max 23 du/ac. § 18.15.050.
• FAR (Floor Area Ratio): R‑MF‑4 scaled (e.g., 0.10–0.21 depending on slope/density band); R‑MF‑23 Max 0.55. § 18.15.050.
• Principal building height: typically max 34 ft / vertical 28 ft for R‑MF‑4; max 38 ft / 3 stories for R‑MF‑23 (vertical 34 ft). § 18.15.050.
• Setbacks: Front: 30 ft (unless special setbacks apply — Alpine Road corridor may be 75 ft); Interior side and rear vary by subdistrict (see table). § 18.15.050 and Chapter 18.58 for special setback lines.

Practical guidance

• Multi‑family projects must check the applicable density band and slope adjustments (FAR and CAR change with du/ac bands) and confirm building separation and LAR (landscape area ratio) before preliminary design. See § 18.15.050.

M‑U (Mixed‑Use) — M‑U1, M‑U2

Purpose and where it applies

• The M‑U districts are for mixed residential + local commercial/office near identified parcels (including specific supportive‑housing overlays for some Alpine Road parcels). See § 18.23.050.

Typical permitted uses

• Residential (multi‑unit), ground‑floor neighborhood commercial, accessory uses; accessory uses and parking are listed in § 18.23.040 and § 18.36.040.

Key dimensional standards

• Density: Min 3 du/ac, Max 6 du/ac. § 18.23.050.
• FAR (residential): Max 0.28 (residential); FAR non‑residential Max 0.22 (note: Supportive Housing Overlay may change these limits for specific parcels). § 18.23.050.
• Building height: Principal structure max 34 ft (vertical 28 ft). Accessory structures max 16 ft. § 18.23.050.
• Setbacks: Front 30 ft (but 75 ft along Alpine Road scenic corridor per Chapter 18.58); street side min 25–30 ft; interior side min 15 ft; rear min 25 ft. § 18.23.050 and § 18.58.020.

Practical guidance

• M‑U projects have additional design rules in § 18.23.060 (building transparency, mixed‑use circulation and residential building design rules) — those affect façade design and the location of entries. § 18.23.060.

R‑E (Estate Residential) — R‑E

Purpose and where it applies

• R‑E is the Town’s rural/estate residential district (large lot/sensitive terrain). Rules and accessory uses are described in § 18.12.040 and elsewhere.

Typical permitted uses

• Single‑family dwellings, accessory uses (including equestrian uses where allowed), and public parks/uses consistent with the General Plan. See § 18.12.040.

Key dimensional standards (summary)

• Many dimensional rules for accessory uses and lot coverage come from the general accessory structure rules (Chapter 18.42) and the district tables (Table 1 in the code). See § 18.42.010 for accessory structure yard/height coverage requirements and Table No. 2 for specific area/bulk regs.

Practical guidance

• Projects in R‑E should expect strict landscape and ASCC design review (see design review), and to be subject to slope, geologic, and special setback constraints. Check combining districts (e.g., 1A, 2A, slope density) in § 18.06.020.

One-table at-a-glance: most decision‑relevant numeric standards

ADUs (Accessory Dwelling Units) — short, Portola‑specific notes

• The Town’s Zoning Code includes an ADU regulatory subsection in the Title 18 extracts we reviewed; the code recognizes the state ADU exemptions and also imposes Town safety/geologic exceptions and capacity/AMFA considerations. The Town text in the uploaded excerpts requires verification of the local ADU section number in the full code; the ADU text excerpts in the files are present but the section header number for that ADU subsection was not visible in the extracted fragments I received. See the Town code excerpts that include ADU development‑standards language (uploaded material) and the state ADU law background for what the Town may not override.

What the uploaded excerpts do show (grounded text)

• The Town permits ministerial ADUs consistent with state law, and identifies safety exceptions (fire access/ingress‑egress, geologic restrictions) that can prohibit ADUs in specific parcels. The upload text spells out items such as: prohibition of ADUs where access is from a road with a single point of ingress/egress narrower than 18 ft; geologic exclusions where construction is prohibited per the Town’s Geologic Regulations; and numeric allowances for ministerially permitted small ADUs (e.g., a detached 800‑sf, 16 ft high ADU with 4 ft side/rear setbacks in some circumstances). These provisions appear in the Town excerpts I was given but the controlling local § number was not visible in the extract. See the local excerpt for the ADU policy language.

State backstops you should expect to apply

• State ADU law sets minimum allowances (e.g., detached ADU baseline 16 ft height, 4 ft side/rear setbacks; ministerial processing and limits on lot‑size and parking restrictions). The Town’s ADU provisions reference that state framework — so confirm Town text against Government Code requirements. See the Town ADU excerpt and the ADU handbook excerpts in the files.

Action item (ADUs)

• Because the file extract containing ADU development standards did not display a clear numbered § in the material I received, verify the controlling Town section number on the Town website or with Planning staff before relying on any single numeric limit. Verify ADU applicability when the parcel is in geologic setback or has special ingress/egress conditions. Not found in retrieved materials: a single explicit local § number for the ADU subsection — Verify with the jurisdiction.

Checklist — what an applicant must satisfy (preliminary)

• Confirm zoning district and any combining districts (e.g., design review D‑R, slope density 7.5M/15M etc.) — see § 18.06.020.
• Confirm numeric limits from the district table that applies (e.g., § 18.15.050 for R‑MF or § 18.23.050 for M‑U).
• Check special setback lines (Alpine, Portola, Skyline) in Chapter 18.58; these can override district setbacks. § 18.58.020.
• Verify FAR/CAR/AMFA/Adjusted AMFA calculations if parcel has slope, ground‑movement, or flood constraints (see Tables and AMFA computation references in Title 18). § 18.50.041 and related AMFA guidance.
• Confirm parking requirements and any allowable reductions; consult the Town’s parking page and the code.
• For projects subject to ASCC design review, prepare ASCC submittals and stake building footprints/story poles as required (§ 18.64.045).
• If proposing ADUs: check Town ADU rules and safety/geologic exceptions (verify local ADU section in Town code and State ADU law). Not found in retrieved materials: single local ADU § number — verify with the jurisdiction.

Risks & Ambiguities

Plain‑English Summary

Portola Valley’s zoning tables give you the hard numbers: each district (for example R‑MF‑4, R‑MF‑23, M‑U1/M‑U2) sets a density range, a FAR and CAR cap, a maximum building height, and minimum setbacks; scenic and geological special setback lines (Chapter 18.58) can increase required front or corridor setbacks (e.g., Alpine Road, Skyline), and ASCC design review and geologic or fire safety rules frequently constrain where you can place buildings. Check the district table that applies to your parcel (e.g., § 18.15.050 for multi‑family or § 18.23.050 for mixed‑use), then check overlay/special setback maps and AMFA/IAR computations.

Source References

• Portola Valley Title 18 — R‑MF development standards: § 18.15.050 (Table 18.15.050)
• Portola Valley Title 18 — M‑U development standards: § 18.23.050 (Table 18.23.050) and design standards § 18.23.060.
• Portola Valley Title 18 — Special setback lines (scenic; Portola/Alpine/Skyline): Chapter 18.58 (notably § 18.58.020 and § 18.58.030).
• Portola Valley Title 18 — Height exceptions: § 18.54.030.
• Portola Valley Title 18 — Accessory structures (yards/height/coverage): § 18.42.010 and related accessory rules.
• Portola Valley Title 18 — SB9 standards (lot split / two‑unit rules): § 18.27.060 (SB 9 Development Standards).
• Portola Valley Title 18 — Definitions, slope/density combining districts and AMFA/IAR computation references: §§ 18.06.020, 18.50.041 and Table computations.
• Town ADU excerpts and local ADU policy language (excerpt in uploaded materials; verify local §): local ADU development‑standards text in extracted file (ADU text appears in the provided materials but the specific local subsection number was not clear in extracted fragments) — verify with the Town.
• State ADU and ADU handbook citations (background on state minimums and constraints): “2025 California ADU handbook” excerpts in uploaded materials (state law citations summarized).

Retrieved passages

• California Building Code High relevance show source text
• Portola Valley Zoning Code (Chapter 18.58) High relevance show source text
• Portola Valley Zoning Code (§ 1) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.54.040) High relevance show source text
• CBC § 66314 (§ 66314) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.64) High relevance show source text
• Portola Valley Zoning Code (§ 66314) High relevance show source text
• Portola Valley Zoning Code (§ 66317) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.72) High relevance show source text
• Portola Valley Zoning Code (section of) High relevance show source text
• Portola Valley Zoning Code (Section 21155) High relevance show source text
• Portola Valley Zoning Code (section shall) High relevance show source text
• Portola Valley Zoning Code (Section 18.36.020) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.74) High relevance show source text
• Portola Valley Zoning Code (Section 6) High relevance show source text
• Portola Valley Zoning Code (§ 9) Medium relevance show source text
• Portola Valley Zoning Code (§ 1) Medium relevance show source text
• Portola Valley Zoning Code (§ 7) Medium relevance show source text
• Portola Valley Zoning Code (§ 2) Medium relevance show source text
• Portola Valley Zoning Code (TITLE 18) Medium relevance show source text
• Portola Valley Zoning Code (chapter that) Medium relevance show source text
• Portola Valley Zoning Code (Section 18.43.030.A.) High relevance show source text
• Portola Valley Zoning Code High relevance show source text

Cited sections

• Portola Valley Title 18 — R‑MF development standards: § **18.15.050** (Table 18.15.050) (Title 18)
• Portola Valley Title 18 — M‑U development standards: § **18.23.050** (Table 18.23.050) and design standards § **18.23.060**. (Title 18)
• Portola Valley Title 18 — Special setback lines (scenic; Portola/Alpine/Skyline): Chapter **18.58** (notably § **18.58.020** and § **18.58.030**). (Title 18)
• Portola Valley Title 18 — Height exceptions: § **18.54.030**. (Title 18)
• Portola Valley Title 18 — Accessory structures (yards/height/coverage): § **18.42.010** and related accessory rules. (Title 18)
• Portola Valley Title 18 — SB9 standards (lot split / two‑unit rules): § **18.27.060** (SB 9 Development Standards). (Title 18)
• Portola Valley Title 18 — Definitions, slope/density combining districts and AMFA/IAR computation references: §§ **18.06.020**, **18.50.041** and Table computations. (Title 18)
• Town ADU excerpts and local ADU policy language (excerpt in uploaded materials; verify local §): local ADU development‑standards text in extracted file (ADU text appears in the provided materials but the specific local subsection number was not clear in extracted fragments) — verify with the Town.
• State ADU and ADU handbook citations (background on state minimums and constraints): “2025 California ADU handbook” excerpts in uploaded materials (state law citations summarized).
• PortolaValley_ZoningCode.md
• 2025 California ADU handbook.md

• Official Portola Valley code library