Hillsborough — Nonconforming Uses

Last reviewed: July 2, 2026

Overview

This page explains how the Town of Hillsborough treats nonconforming uses, nonconforming structures, and nonconforming zoning conditions under the local zoning code (Title 17). It synthesizes the Town's rules about when a nonconforming use must stop, what work is allowed on legally nonconforming buildings, rebuilding after disaster, and how accessory dwelling unit (ADU) rules interact with nonconformities. Key controlling provisions are cited so you can verify language in the code. Verify with the jurisdiction for parcel‑specific determinations.

What Hillsborough’s code says — core rules

• A use that was legal when established but that later fails to meet the zoning code is a legal nonconforming use (definition found in § 17.20.010) and is governed by Chapter 17.20 and related chapters.

• If a legal nonconforming use stops for 180 consecutive days, the use cannot resume and the property must thereafter comply with the current code; see § 17.20.040.

• Work allowed on nonconforming structures in the absence of disaster is limited:

  • Encroachments into setbacks may be altered or enlarged only if the encroachment does not extend further into the setback, the new portion within the setback is no taller than 22 feet, the fire chief and building official find no safety hazard, and the Architecture and Design Review Board approves that the work is not materially detrimental — § 17.20.020(A).
  • Garages may be completely reconstructed by a garage exception from the Architecture and Design Review Board if the board finds the replacement is beneficial and not detrimental — § 17.20.020(B).
  • Alterations that would raise an existing nonconforming building’s FAR, lot coverage, or accessory‑structure size are allowed only so long as the work does not increase the net amount of nonconforming floor area or footprint; see § 17.20.020(C) (cross‑references § 17.32.030(B) on FAR).
  • Nonconforming height may be altered or enlarged only within the existing building envelope and no new construction shall exceed the existing height unless the Architecture and Design Review Board recommends otherwise — § 17.20.020(D).

• Rebuilding after natural disaster: a legal nonconforming structure destroyed by fire, earthquake, or other natural disaster may be rebuilt to the same or a lesser degree of nonconformity; intentional removal disqualifies rebuilding — § 17.20.030.

• Special rules: certain older features (for example, night lighting of tennis courts installed before December 9, 2002) are treated as nonconforming structures and remain subject to Chapter 17.20 limits (including curfew hours) — § 17.20.050.

• ADUs and nonconforming conditions: the ADU chapter clarifies that the Town will not deny an ADU or JADU application because of a nonconforming zoning condition, a building‑code violation, or an unpermitted structure unless that condition presents a threat to public health and safety or is affected by the ADU construction — see § 17.52.020(B) and the ADU-specific nonconforming provisions in Chapter 17.52.

(For the ADU program’s setbacks, parking, height, and ministerial review rules see Chapter 17.52 — those rules explicitly address how ADUs interact with preexisting nonconforming conditions.)

District-by-district (Hillsborough-specific)

The Hillsborough code organizes primary residential zoning around the "RD" districts. The code also lists specific legal nonconforming uses that pre‑date the ordinance. Below are the district summaries that are explicitly defined in the retrieved materials.

RD-1 (Traditional Residential)

• Purpose: preserve the single‑family character of Hillsborough and limit density; maximum density is one dwelling per one‑half acre (exclusive of ADUs). § 17.16.010(A)(1).
• Typical permitted uses: single‑family dwellings, accessory structures, country club (listed specifically), public parks/playgrounds, town facilities where applicable; see use table in § 17.16.010(B).
• Key dimensional/approval notes that affect nonconforming situations:
  • General street‑line setback definition is 25 ft (the street‑line setback area is described in § 17.24.020), which is the baseline for setback nonconformity decisions.
  • Work that would further encroach into setbacks is limited by § 17.20.020(A) (see above).
• Where it applies: the code indicates RD-1 covers the Town’s single‑family neighborhoods and includes the allowed use table; see § 17.16.010(B) for specifics.

RD-2 (Mixed Residential)

• Purpose: accommodate townhomes and multifamily buildings on certain town‑owned land; minimum allowed density 20 units/acre. § 17.16.010(A)(2).
• Typical permitted uses: multifamily housing, public parks, some town facilities, and accessory uses listed in the uses table § 17.16.010(B).
• Key dimensional/approval notes:
  • ADUs and two‑unit projects are subject to the ADU and two‑unit chapters (Chapters 17.52 and 17.54); nonconforming conditions for ADUs follow the ADU rules (Town will not deny ADUs due solely to nonconforming zoning conditions that do not threaten health or safety) — § 17.52.020(B).
  • Any project proposing a change of use or new construction will be held to chapter‑specific standards and may trigger correction of some nonconformities as described in the applicable chapter (see 17.54 for two‑unit projects).
• Where it applies: specific town‑owned parcels identified in the code; see § 17.16.010(A)(2).

RD-3 (Governmental & Residential Mixed Use)

• Purpose: accommodate town facilities and limited residential units on specified town land; maximum units identified in the code (example: up to 16 dwelling units on land zoned RD‑3). § 17.16.010(A)(3).
• Typical permitted uses: town facilities, limited residential, public buildings, public parks, and other uses listed in § 17.16.010(B).
• Key dimensional/approval notes: RD‑3 projects that create new dwellings are subject to the Town’s density bonus, ADU, and two‑unit project rules where applicable; nonconforming structures on a lot redeveloped under RD‑3 will be addressed under the specific chapter that governs the project (e.g., 17.54, 17.52, design review).
• Where it applies: town‑owned land identified by the code.

Note: the retrieved materials do not present a full list of every Hillsborough zoning district (for example commercial district designations named "C‑" were not found in the provided excerpts). Verify the zoning map or full Title 17 for any district not summarized above. Not found in retrieved materials: an exhaustive list of all zoning district codes and the full dimensional schedule for each district.

Quick table — decision‑relevant rules and code references

Practical guidance / synthesis (plain English, applied)

• If you own a house in Hillsborough with an older feature that doesn’t meet today’s code (for example, a setback encroachment, an oversized garage, or a historic accessory building), it may be a legal nonconforming structure — you can usually repair, maintain, and in many cases remodel it so long as you do not extend the specific nonconformity (see § 17.20.020).

• If the nonconforming use (for example, a small commercial use in a residential district) stops operating for 180 days, the Town requires the property to convert to a conforming use before resuming operation. Document continuous operation if you want to preserve a nonconforming commercial or institutional use. § 17.20.040.

• When planning an ADU on a property with nonconforming site conditions, the ADU chapter protects applicants from being blocked just because the lot has a preexisting nonconforming condition — the Town may only require correction when the nonconformity is a health/safety threat or is affected by the ADU construction (Chapter 17.52).

• For setback disputes, remember the Town defines a 25‑foot street‑line setback area and limits how far into setbacks a nonconforming structure can be further altered — consult § 17.24.020 and § 17.20.020(A) early in design.

Checklist — what an applicant must satisfy (before applying)

• Confirm whether the existing feature/use is a legal nonconforming use or structure (collect historic permits, certificates of occupancy). Verify under § 17.20.010 and the Town’s list of legal nonconforming uses.
• If the nonconforming use stopped, confirm continuous use history (to avoid the 180‑day abandonment rule in § 17.20.040).
• If proposing alterations that affect setbacks, get pre‑application review with Building & Planning and note the 22‑ft limitation for new portions in setback areas and required findings by Design Review and safety officials (§ 17.20.020(A)).
• For ADUs, follow Chapter 17.52’s ministerial checklist and note that nonconforming zoning conditions are generally not a ground for denial absent health/safety impacts — see § 17.52.020(B).
• Provide any required design review submittals (see the Town’s Hillsborough Design Review process) and consult the Hillsborough Development Standards and Hillsborough Parking rules if required.
• Check for overlay or historic district status (see Hillsborough Overlay Districts and Hillsborough Historic Preservation) — these can change what is permitted for nonconforming features.
• Verify building code compliance with the California Building Standards Code for any structural repairs or reconstruction.

Risks & Ambiguities

Plain‑English summary

If something on your Hillsborough property was legal when it was built but no longer complies with today’s zoning, it can usually stay — but you can’t let the use lapse for 180 days or expand the illegal part; limited repairs and some remodeling are allowed if they don’t worsen the nonconformity. The Town also limits what you can do inside setback areas, lets you rebuild after a disaster to the same or smaller nonconformity, and protects ADU applicants from being blocked simply by nonconforming site conditions unless there’s a health/safety problem (see § 17.20.020, § 17.20.030, § 17.20.040, and Chapter 17.52).

Information Gaps

• Full dimensional schedules (side/rear/front setbacks by district, maximum lot coverage percentages, FAR by district) are not contained in the retrieved excerpts — verify in the Town’s full Title 17 or the Development Standards table. Not found in retrieved materials.
• A complete list of all zoning district names and the Town zoning map were not included in the materials returned. Not found in retrieved materials.
• Specific procedures or forms to document continuous operation for nonconforming uses (for the 180‑day rule) are not included; contact the Planning Department. Not found in retrieved materials.

Source References

• Hillsborough Municipal Code, Title 17 — Nonconforming uses and structures: § 17.20.020, § 17.20.030, § 17.20.040, § 17.20.050.
• Hillsborough Municipal Code — Uses permitted and legal nonconforming uses, RD districts: § 17.16.010 (RD‑1, RD‑2, RD‑3 and legal nonconforming uses such as Hillsborough Racquet Club).
• Hillsborough Municipal Code — ADU chapter and nonconforming zoning condition protections: Chapter 17.52 (including § 17.52.020 and § 17.52.030) and ADU ministerial/exception rules.
• Setback rules: Chapter 17.24 including § 17.24.020 (street‑line setback definition).

Retrieved passages

• Hillsborough Zoning Code (Section 17.32.030) High relevance show source text
• Hillsborough Zoning Code (§ 16) High relevance show source text
• Hillsborough Zoning Code (§ 16) High relevance show source text
• CBC § 3 (Section 65852.2) High relevance show source text
• Hillsborough Zoning Code (§ 66333) High relevance show source text
• CBC § 66321 (§ 66321) High relevance show source text
• California Fire Code High relevance show source text
• Hillsborough Zoning Code (§ 66314) High relevance show source text
• Hillsborough Zoning Code (§ 3) Medium relevance show source text
• California Fire Code Medium relevance show source text
• CBC § 65852.2 (Section 65852.2) Medium relevance show source text
• CBC § 66314 (§ 66314) Medium relevance show source text
• Hillsborough Zoning Code (Section 26001) Medium relevance show source text
• Hillsborough Zoning Code (Section 17.16.020) Medium relevance show source text

Cited sections

• Hillsborough Municipal Code, Title 17 — Nonconforming uses and structures: **§ 17.20.020**, **§ 17.20.030**, **§ 17.20.040**, **§ 17.20.050**. (Title 17)
• Hillsborough Municipal Code — Uses permitted and legal nonconforming uses, RD districts: **§ 17.16.010** (RD‑1, RD‑2, RD‑3 and legal nonconforming uses such as Hillsborough Racquet Club). (§ 17.16.010)
• Hillsborough Municipal Code — ADU chapter and nonconforming zoning condition protections: Chapter **17.52** (including **§ 17.52.020** and **§ 17.52.030**) and ADU ministerial/exception rules. (chapter and)
• Setback rules: Chapter **17.24** including **§ 17.24.020** (street‑line setback definition). (§ 17.24.020)
• Hillsborough_ZoningCode.md

• Official Hillsborough code library