Portola Valley — Nonconforming Uses

Last reviewed: July 2, 2026

Overview

This page summarizes how Portola Valley’s zoning ordinance treats nonconforming uses, nonconforming structures, and nonconforming lots under the town zoning code (chapters numbered in the 18.x series). It explains what may be continued, repaired, replaced, changed, or lost, and how the rules interact with special setbacks, design review, and conditional-use procedures. All rules below are grounded in the Portola Valley Municipal Code — relevant §§ are cited and the ordinance extracts used are referenced.

How Portola Valley treats nonconforming situations — the essentials

• Continuation: Any legally existing nonconforming structure or use may be continued unless another provision of the title says otherwise ( § 18.46.010 ).
• Repairs and maintenance: Routine repairs and maintenance are allowed to keep a nonconforming structure or a structure occupied by a nonconforming use in sound condition ( § 18.46.020 ).
• No enlargement/expansion: A nonconforming use may not be enlarged, extended, reconstructed or structurally altered to increase the extent of nonconformity except as expressly authorized ( § 18.46.070 ).
• Substitution/changes: The Planning Commission may authorize substitution of one nonconforming use for another or modifications in character/intensity/hours by conditional use permit following Chapter 18.72 procedures ( § 18.46.080 ).
• Cessation/abandonment: Time frames after which a use or structure loses its nonconforming status are strict — commonly 12 months, 6 months, or 90 days depending on the type of structure/use ( § 18.46.090 ).
• Damage / reconstruction: If involuntary damage equals or exceeds 50% of the structure’s current appraised value, reconstruction rules change — sometimes requiring full compliance with current zoning or ASCC approval (see § 18.46.030 and § 18.46.040 ). An independent appraiser retained by the owner and approved by the town determines the current appraised value ( § 18.46.030.E ).

Note: earthquake fault setbacks and creek-setback rules impose additional restrictions on reconstruction after damage; see § 18.46.050 and the creek setback chapter.

District-by-district breakdown (where nonconforming rules apply)

Below are the Portola Valley districts explicitly described in the zoning code excerpts I reviewed. For each I list the district purpose, typical permitted uses, key dimensional/development standards, and where it commonly applies. Always verify the exact parcel zoning on the town zoning map (Verify with the jurisdiction).

R-1 (Single‑Family Residential)

• Purpose: To promote single‑family rural-urban living, preserve visual open space and privacy. § 18.14.010.
• Typical permitted uses: Single‑family dwelling, allowed accessory uses, group homes of six or fewer, supportive or transitional housing as listed in the chapter. § 18.14.020.
• Key dimensional standards: R‑1 parcels are governed by the combining district parcel areas and yards shown in Table No. 1 (parcel-area / yards / height / max floor area / max impervious surface) in § 18.48.010. Examples: 20 ft front yard, 20 ft rear yard, side setbacks that vary by combining district and parcel size; height limits shown in the table.
• Where it applies: Town single‑family neighborhoods; nonconforming residential structures in R-1 follow the general nonconforming rules in Chapter 18.46.

R‑MF (Multi‑Family Residential)

• Purpose: To provide for multi‑family dwellings while protecting open space and privacy. § 18.15.010.
• Typical permitted uses: Principal multi‑family residential uses and specified conditional uses; accessory uses per other chapters. § 18.15.010–.040.
• Key dimensional standards: Development standards and design standards are incorporated within the R‑MF chapter and general Chapters 18.48–18.56 (yards, height, floor area). Nonconforming buildings in R‑MF are subject to Chapter 18.46.

D‑R (Development‑Restriction / Scenic / Resource; Skyline area)

• Purpose: Protect scenic corridors and natural resources along Skyline Boulevard; restrict grading, tree removal and disturbance. § 18.30.010–.050.
• Typical permitted uses: Uses are tightly restricted; special design and ASCC review apply. § 18.30.030 requires ASCC review for building permits.
• Key dimensional standards: Special limits on site disturbance, access and setbacks; nonconforming structures in D‑R remain governed by Chapter 18.46, but reconstruction in some cases may require additional ASCC review.

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

• Purpose and uses: These non‑residential districts carry landscaping and parking requirements and allow commercial/administrative uses when authorized. They are subject to the same nonconforming-use rules in Chapter 18.46, and special landscaping and impervious‑surface rules appear in Chapters 18.56 and related tables.
• Dimensional standards: Table No. 1, Chapters 18.48–18.56, and conditional-use provisions control bulk, coverage and impervious-surface allowances.

Accessory structures

• Detached accessory structures are generally required to conform to yard/height/coverage requirements (see Chapter 18.42), but repairs to nonconforming accessory structures are allowed under § 18.46.020.

Notes on district breakdown: The code organizes parcel-size combinations and dimensional rules in Table No. 1 under § 18.48.010; these are the numeric standards commonly used to assess whether a building or lot is nonconforming. For parcel‑specific limits (e.g., exact front setback or maximum floor area for a parcel), use Table No. 1 and the combining district tables in Chapters 18.48–18.56.

Quick decision table — most action‑relevant nonconforming standards

How these rules interact with other local processes and standards

• Design review: If reconstruction triggers architectural and site plan review (ASCC), the ASCC must approve design changes; see Chapter 18.64 for ASCC applicability and procedures. Design review is a common step when nonconforming buildings are rebuilt or altered.
• Conditional use / planning commission: Substitution or modification of a nonconforming use typically requires a conditional use permit from the Planning Commission under Chapter 18.72 (see § 18.46.080).
• Development standards and setbacks: Numeric setbacks, floor‑area and impervious‑surface standards used to judge nonconformity are in Table No. 1 and Chapters 18.48–18.56 — check the development standards for the parcel’s combining district.
• Parking: Any change of use or expansion that would affect parking must meet the off‑street parking standards in Chapter 18.60, unless a waiver or conditional use modification is granted.

(Helpful internal links: the town’s pages on design review, development standards, parking, overlay districts, ADUs, and the California Building Standards Code are commonly consulted with nonconforming questions.)

Checklist — what an applicant must gather (minimum)

• Proof of legal existing use/structure (historic permits, certificates of occupancy, dated photographs, tax/utility records). (Verify with the jurisdiction.)
• If repair/reconstruction follows damage, independent appraisal showing current appraised value if damage is disputed (owner retains appraiser; appraiser must be approved by town). § 18.46.030.E.
• Site plan showing pre‑damage vs proposed footprint, heights, impervious surfaces and how the proposal would or would not enlarge nonconformity. § 18.46.030 / § 18.46.040.
• If substitution or intensification is proposed, a conditional use permit application per Chapter 18.72 and findings showing similar or lesser intensity ( § 18.46.080 ).
• If size of reconstruction exceeds fifty percent or is in a special setback (fault or creek), engineering, geologic or creek‑study reports as required by Chapters 18.46, 18.58, or 18.59; ASCC design materials if applicable. § 18.46.050 and Chapter 18.64.
• Parking impact assessment and evidence that off‑street parking meets Chapter 18.60 (or a conditional use / modification to deviate).

Risks & Ambiguities

Plain‑English summary

If your home or business in Portola Valley was built or used in a way that no longer matches the zoning rules, you can usually keep that use or structure — but you cannot expand it and there are strict rules if it’s damaged or removed. Small repairs are allowed; big rebuilds (or voluntary demolitions) and changes of use typically require town review, possible conditional‑use permits, ASCC design approval, and in many cases must meet current standards. Key controlling rules are in Chapter 18.46 (nonconforming uses/structures) and the parcel‑specific development standards in Chapters 18.48–18.56.

Source References

• Portola Valley Municipal Code — Chapter 18.46 (Nonconforming Structures and Uses) — see § 18.46.010 et seq.
• § 18.46.020 (Repairs to nonconforming structure) and related procedural text.
• § 18.46.030 (Replacement after involuntary damage; appraisal requirement) and § 18.46.040 (Voluntary demolition).
• § 18.46.050 (Earthquake fault setbacks and reconstruction rules).
• § 18.46.060–.080 (Conditional uses, prohibition on expansion, substitution rules via Planning Commission under Chapter 18.72).
• § 18.46.090 (Cessation/abandonment timelines: 12 months, 6 months, 90 days).
• § 18.48.010 (Table No. 1 — Basic area, open space, bulk and density regulations: parcel area, yards, height, floor area, impervious surface).
• Chapter 18.64 (Architectural and Site Plan Review — ASCC applicability) which is referenced for design approvals.
• Chapter 18.42 (Accessory structures rules, which interact with nonconforming rules) and Chapter 18.59 (creek setbacks/reconstruction).
• Parking and off‑street parking references (Chapter 18.60 and district cross‑references).

If you need direct wording from any specific § or want a parcel-level read (compute whether a particular building is nonconforming), I can pull the exact ordinance language used for the parcel and list the application steps the town will expect. Verify all parcel‑specific conclusions with the Town of Portola Valley planning staff. Verify with the jurisdiction.

Retrieved passages

• Portola Valley Zoning Code (title for) High relevance show source text
• Portola Valley Zoning Code (§ 4) High relevance show source text
• Portola Valley Zoning Code (§ 1) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.64.) High relevance show source text
• Portola Valley Zoning Code (Chapter 18.60.) High relevance show source text
• Portola Valley Zoning Code (§ 2) Medium relevance show source text
• Portola Valley Zoning Code (Chapter 18.72) Medium relevance show source text
• Portola Valley Zoning Code (title taking) Medium relevance show source text

Cited sections

• Portola Valley Municipal Code — **Chapter 18.46 (Nonconforming Structures and Uses)** — see **§ 18.46.010** et seq. (Chapter 18.46)
• **§ 18.46.020** (Repairs to nonconforming structure) and related procedural text. (§ 18.46.020)
• **§ 18.46.030** (Replacement after involuntary damage; appraisal requirement) and **§ 18.46.040** (Voluntary demolition). (§ 18.46.030)
• **§ 18.46.050** (Earthquake fault setbacks and reconstruction rules). (§ 18.46.050)
• **§ 18.46.060–.080** (Conditional uses, prohibition on expansion, substitution rules via Planning Commission under Chapter 18.72). (§ 18.46.060)
• **§ 18.46.090** (Cessation/abandonment timelines: 12 months, 6 months, 90 days). (§ 18.46.090)
• **§ 18.48.010** (Table No. 1 — Basic area, open space, bulk and density regulations: parcel area, yards, height, floor area, impervious surface). (§ 18.48.010)
• **Chapter 18.64** (Architectural and Site Plan Review — ASCC applicability) which is referenced for design approvals. (Chapter 18.64)
• **Chapter 18.42** (Accessory structures rules, which interact with nonconforming rules) and **Chapter 18.59** (creek setbacks/reconstruction). (Chapter 18.42)
• Parking and off‑street parking references (Chapter **18.60** and district cross‑references).
• PortolaValley_ZoningCode.md
• 2025 California ADU handbook.md

• Official Portola Valley code library