Local zoning · Portola Valley

Portola Valley — Design Review

Design Review under the Portola Valley local zoning and planning code, with the controlling citations.

Last reviewed: July 2, 2026

Overview

Portola Valley’s local zoning code centralizes design review through the Architectural and Site Control Commission (ASCC) and a separate D‑R (Design Review) combining district. The ASCC process (called “architectural and site plan review” in the code) sets application triggers, required submittals, and guiding principles intended to preserve the town’s rural character and limit grading, tree loss and visual impacts. Key rules and triggers are in § 18.64.010 and the related subparts; supporting combining‑district rules are in § 18.30.010 .

Note: this page covers only what the Portola Valley zoning/land‑use ordinance says about design/architectural/site plan review (not Title 24 or other building code topics). For building-code compliance see California Building Standards Code.

How Portola Valley structures its design review (what the code says)

The ordinance uses the term “architectural and site plan review” and assigns review authority to the Architectural and Site Control Commission (ASCC), with staff and the Planning & Building Director performing ministerial or staff discretionary reviews in some cases § 18.64.020, § 18.64.030 .
The basic purpose is stated as preserving Portola Valley’s visual character, avoiding indiscriminate clearing/excessive grading and protecting public safety and property values § 18.64.010(B) .
Some projects are expressly exempted from the chapter’s architectural/site review (notably SB 9 dwelling units are treated under the town’s SB 9 objective checklist, not ASCC) per § 18.64.015 .
The code specifies the minimum submittals (scaled site plan, elevations, lighting plan, planting plan, grades/drainage certified by an engineer, trash/recycling enclosures, staking of perimeter, and other items as required) in § 18.64.040 .
The ASCC reviews against the town’s adopted design guidelines and guiding principles (compatibility with natural terrain, minimizing disturbance, preservation of vegetation, appropriate massing and materials) in § 18.64.045–§ 18.64.050 .

District‑by‑district breakdown (where design review interacts with local districts)

Below are the districts/combining districts that the ordinance ties to design review or where the ASCC commonly applies rules. For each I cite the controlling code where available; where the retrieved materials lack a specific item I mark that gap.

D‑R (Design Review) combining district

Purpose: Preserve natural qualities, adapt development to site conditions, and protect visual character along major corridors, stormwater/runoff and soil stability objectives § 18.30.010 .
Typical permitted uses: Not found in retrieved materials (the D‑R is a combining district applied in addition to base zoning; base‑zone uses are controlled by the underlying district). Verify with the jurisdiction and the zoning map.
Key dimensional/approval standards: The combining district creates special review expectations (site adaptation, limits on grading/tree removal). Specific numeric standards are not listed in the retrieved D‑R text; rely on the ASCC findings and design guidelines § 18.30.010 and § 18.64.050 .
Where it applies: Shown on the Town Zoning Map and applied as a combining district per § 18.06.030; parcels with D‑R retain their base zone but are subject to additional ASCC review requirements .

M‑U (Mixed Use)

Purpose: Mixed‑use development standards and design controls for pedestrian‑oriented building form are set out in Chapter 18.23.
Typical permitted uses: Mixed residential and nonresidential uses allowed per the M‑U district (full use list not contained in retrieved excerpts). Verify with the full district text.
Key dimensional/design standards: Ground‑floor nonresidential facades must have minimum transparency requirements (40% of ground‑floor street‑facing nonresidential facades between 2.5 and 6 feet must be transparent) and other design/site rules; see § 18.23.060.D–E .
Where it applies: M‑U locations are set on the zoning map; ASCC/design review will consider the M‑U design standards where applicable § 18.23.060 .

C‑C (Community Commercial) and A‑P (Administrative‑Professional)

Purpose: Commercial and administrative/professional uses with landscaping and frontage standards to protect visual character.
Typical permitted uses: Not fully reproduced in retrieved materials — see the underlying district chapters for the use list.
Key standards linked to design review: Parcels in C‑C must maintain at least 30% natural vegetative cover or landscaping; A‑P requires 40% (landscaped or natural cover) within the parcel § 18.56.020.E . ASCC will use landscaping requirements as part of site review.
Where it applies: C‑C and A‑P zoning districts on the zoning map; landscaping percentages are explicit in § 18.56.020 .

R‑1, R‑E/5A and other residential districts

Purpose: Standard single‑family/residential district controls; ASCC review applies to specific building thresholds (see triggers below). The combining districts list identifies multiple residential parcel‑size combining districts (e.g., 1A, 2A, 5A) in § 18.06.020 .
Typical permitted uses: Single‑family dwellings and accessory uses (full use tables are in the base district chapters — not fully reproduced in the retrieved snippets). Verify the base zone chapter for the parcel.
Key dimensional standards relevant to design review: Special setback lines (S) and corridor setbacks are enforced in the code; for example, Skyline Boulevard and Alpine Road special setbacks and Portola Road setback rules are in § 18.58.020.D and D.3 (Portola Road rules) — note ASCC may allow limited reductions where visibility is minimized § 18.58.020 .
Where it applies: All residentially zoned parcels as shown on the zoning map; ASCC review is triggered by the thresholds in § 18.64.010 .

Key decision‑relevant standards and triggers (quick reference table)

Topic / Trigger	What the code requires	Code reference
Buildings or additions ≥ 400 sq ft or two stories — ASCC referral	Architectural and site plan review required for building permits for buildings or additions of 400 sq ft or larger or two stories or more	§ 18.64.010. A.1
All commercial buildings	All building permits for commercial buildings referred for ASCC review	§ 18.64.010. A.2
Parcels fronting arterials / major corridors	Building permits on parcels fronting arterial roads as shown on General Plan are subject to review	§ 18.64.010. A.3
Uncovered parking	Zoning permits for uncovered parking are referred to ASCC	§ 18.64.010. A.14
Tennis / paddle courts	Zoning permits for tennis and paddle tennis courts require review	§ 18.64.010. A.6
SB 9 small‑lot duplex units	Exempt from Chapter 18.64 ASCC process; handled ministerially under SB 9 checklist	§ 18.64.015
Minimum design submittals	Site plan, elevations, lighting plan, planting plan, grades/drainage cert., trash/recycling enclosure, staking, and other data as required	§ 18.64.040
Design guidelines requirement	Applications should be prepared using Town Design Guidelines; ASCC uses the Guidelines in review	§ 18.64.045
M‑U facade transparency	40% ground‑floor street‑facing transparency required (2.5–6 ft band)	§ 18.23.060.D

How review is assigned (types of review)

Ministerial review is done by the Planning & Building Director (no public hearing/notice required), but the applicant must still notify adjacent neighbors on an approved form. ADUs that meet state ministerial criteria follow this path § 18.36.040 / types of review .
Staff discretionary review is performed by the Director in consultation with an ASCC member for certain ADUs and similar projects; the Director may refer projects to the full ASCC § 18.36.040 (Types of Review) .
ASCC (full commission) discretionary review occurs at a noticed public meeting for projects the Director/staff refer or for matters specifically required by the code § 18.36.040 .

Checklist — what applicants must provide for an ASCC/substantive design review

A scaled site plan showing parcel dimensions, existing & proposed structures (location, size, height, uses), yards/open spaces, walls and fences, parking and circulation, access points (pedestrian/vehicular/equestrian), signs, loading areas and easements § 18.64.040.A.1–8 .
Architectural drawings or sketches: floor plans and all exterior elevations § 18.64.040.B .
Exterior lighting plan (fixture type, location, intensity and control method) § 18.64.040.A.9 .
Planting/landscaping plan consistent with town landscape guidelines and native plant list § 18.64.040.A.12 and Portola Valley Landscaping and Screening.
Existing and proposed grades and a drainage plan certified by a civil engineer or licensed surveyor § 18.64.040.A.13 .
Trash and recycling enclosure details compliant with § 18.37.010, if applicable § 18.64.040.A.14 and see Portola Valley Parking for parking relationships.
On‑site staking of the perimeter of proposed structures and, when required, story poles, balloons or ridge strings to demonstrate bulk § 18.64.040.D .
Any additional specialized reports requested by staff (e.g., geotechnical for grading, health‑department approval for septic‑dependent ADUs) § 18.36.040 .
If the proposal is in an overlay (for example D‑R or S setback corridors), include any overlay‑specific materials; see Portola Valley Overlay Districts and § 18.30.010 .

Risks & Ambiguities

Issue	Why it matters	What to verify
SB 9 exemption for design review	SB 9 dwelling units are processed under an objective checklist rather than ASCC review; relying on ASCC process could delay an SB 9 project	Verify whether your project is an SB 9 qualifying lot and follow § 18.64.015
ADU ministerial vs discretionary	ADUs may be ministerial, staff discretionary, or ASCC depending on size, height, grading, and impacts; incorrect assumption leads to wrong notice/timeline	Check § 18.36.040 for ADU review assignment and findings required for discretionary approval
Noticing & appeal steps (ASCC notice mechanics)	Some ADU and discretionary reviews require applicant‑provided neighbor notices in specific formats; missing notice can void decisions	Confirm the exact noticing requirements and forms referenced by § 18.36.040 and § 18.64.085 (18.64.085 exists in the code but full text was not in the retrieved excerpts; Verify with the town)
Parcel‑specific overlay or special setback (e.g., Portola Road, Skyline)	Special setback rules can be stricter than base district setbacks and ASCC may require additional planting or envelope limits § 18.58.020	Verify whether your parcel lies inside an S setback or other special overlay on the zoning map § 18.06.030
Use lists and dimensional numbers per base zone	This guide summarizes ASCC interactions, but full permitted‑use lists and numbers (FAR, lot coverage, numeric setbacks for each base district) are in other chapters not fully reproduced here	Review the underlying district chapter and Portola Valley Development Standards; Verify with planning staff

Plain‑English summary

Portola Valley requires architectural and site plan review for a broad set of projects (notably additions ≥400 sq ft, two‑story buildings, commercial buildings, projects on arterial corridors, and other items listed in the code). The ASCC (or staff under delegated authority) uses a town design guidelines checklist plus required plans (site plan, elevations, planting, lighting, drainage) to decide if a project fits the town’s rural, low‑impact character. See § 18.64.010–§ 18.64.050 for triggers, submittals and design principles .

Source References

Portola Valley Municipal Code, Chapter 18.64 (Architectural and Site Plan Review) — applicability, purpose, triggers, exemptions (SB 9), referrals, submittal requirements: § 18.64.010 – § 18.64.050 .
Portola Valley Municipal Code, Chapter 18.30 (D‑R Design Review Combining District) — purpose of D‑R: § 18.30.010 .
Portola Valley Municipal Code, Chapter 18.36 (Accessory Dwelling Units) — review types, ministerial vs discretionary ADU thresholds and findings for ADU discretionary approvals: § 18.36.040 (ADU review excerpts) .
Portola Valley Municipal Code, Chapter 18.23 (M‑U design standards) — ground‑floor transparency and M‑U design rules: § 18.23.060 .
Portola Valley Municipal Code, Chapter 18.56 (Landscaping) — landscaping percentages for C‑C and A‑P: § 18.56.020 .
Portola Valley Municipal Code, Chapter 18.58 (Special setback lines) — Portola Road, Skyline, Alpine Road setback rules and ASCC flexibilities: § 18.58.020 .
Portola Valley Municipal Code, Chapter 18.06 (Combining districts and zoning map) — combining districts including D‑R and application via the zoning map § 18.06.020–§ 18.06.030 .
For building‑code work and separate plan review: California Building Standards Code (state Title 24 guidance — not covered by town design review) .

Sources

Retrieved passages

Portola Valley Zoning Code (§ 1) High relevance
Portola Valley Zoning Code (§ 1) High relevance
Portola Valley Zoning Code (§ 2) High relevance
Portola Valley Zoning Code (Chapter 18.72) Medium relevance
Portola Valley Zoning Code (title taking) Medium relevance
Portola Valley Zoning Code (Section 18.37.010) Medium relevance
Portola Valley Zoning Code (Section 18.64.085) Medium relevance
CBC § 18.64.085 (Section 18.64.085) Medium relevance

Cited sections

Official Portola Valley code library

Frequently asked questions

Do I always need ASCC review for a home addition in Portola Valley?

If your addition is 400 sq ft or larger, or will create a second story, ASCC (architectural and site plan) review is required per § 18.64.010.A.1. Smaller additions may still be referred at the Town’s discretion; verify with the Town Planner or Director before submitting .

What triggers design review for commercial projects?

All commercial building permits are subject to architectural and site plan review under § 18.64.010.A.2; the ASCC evaluates site layout, landscaping, lighting, building materials and compatibility with the rural context .

Are ADUs subject to ASCC review in Portola Valley?

ADU review depends on size, height and other characteristics. Some ADUs are ministerial; others require staff discretionary or full ASCC review. See the ADU review assignment and required findings in § 18.36.040; ministerial ADUs must still meet objective standards and state ADU law where applicable .

What submittals will the ASCC require?

The code lists required materials including a scaled site plan, elevations, an exterior lighting plan, a planting plan, certified grades/drainage, trash/recycling enclosure details, and staking or story poles to show bulk § 18.64.040 .

Is my parcel’s special setback (e.g., Portola Road, Skyline) relevant to design review?

Yes. Special setback lines and scenic corridor setbacks are in § 18.58.020; ASCC may allow limited reductions only if visibility is minimized. Check whether your parcel is subject to S setback mapping on the zoning map § 18.06.030 .

Does the ASCC apply numeric standards or only subjective aesthetics?

The ASCC applies both: it enforces objective submission requirements and numeric overlay/setback rules where present (for example S setbacks in § 18.58.020) and also applies design principles and the Town Design Guidelines when making discretionary findings § 18.64.045–050 .

If I’m building on an arterial street, do I automatically get ASCC review?

Yes — building permits for structures on parcels fronting arterial roads identified in the General Plan are subject to architectural and site plan review § 18.64.010.A.3 .

Are SB 9 duplexes/rear units reviewed by the ASCC?

No. The code explicitly exempts SB 9 dwelling units from the ASCC chapter; SB 9 projects are handled by the Planning & Building Director under the town’s SB 9 objective checklist § 18.64.015 .

Will the ASCC require a planting/landscape palette?

Yes — the code requires a planting plan consistent with the Town’s landscaping guidelines and native plant list as part of the submittals § 18.64.040.A.12; C‑C and A‑P districts also have minimum vegetative cover requirements § 18.56.020 .

How are appeals handled if the ASCC denies a project?

If a zoning permit or certificate of occupancy is withheld for noncompliance, the applicant is advised of appeal procedures to the Board of Adjustment per the ordinance (see the zoning permit and referral procedures in § 18.62.040–§ 18.62.090) .

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