Hillsborough — Overlay Districts

Last reviewed: July 2, 2026

Overview

Hillsborough's Title 17 Zoning ordinance does not establish a separate "overlay district" or explicit "combining/overlay" chapter. The code sets out primary zoning districts, development standards (setbacks, height, coverage), and specialized chapters (ADUs, parking, design review) that operate on top of those base districts — but the specific term "overlay district" does not appear in the retrieved Title 17 materials. Verify parcel- or map-specific designations with the town because site-level restrictions can appear on the zoning map or in separate ordinances. § 17.12.010 and § 17.04.030 explain the primary zoning map and district framework — .

Important links you will see referenced below: the Hillsborough zoning overview, the town's Zoning and Land Use pages, Hillsborough Development Standards, parking, design review, ADUs, and the California Building Standards Code.

What the code says (short answer)

• The code establishes base zoning districts — Traditional Residential (RD‑1), Mixed Residential (RD‑2), and Governmental & Residential Mixed Use (RD‑3) — in § 17.12.010; it does not create a named overlay/combining district in the Title 17 material retrieved. Not found in retrieved materials: any Title 17 section titled or labeled "Overlay District", "Combining District", or similar. Verify with the town for any map notes or separate ordinances that might function as overlays — Not found in retrieved materials — .

District-by-district breakdown (what functions like an overlay would affect)

Note: Hillsborough applies standards across districts via chapters that sit "above" the base zone (setbacks, height envelopes, lot coverage, ADU rules, parking, design review). Where a project would expect an overlay to change allowed uses or standards, those changes in Hillsborough are implemented through code chapters or special permits rather than a labeled overlay. See the cited sections below while preparing an application.

RD‑1 — Traditional Residential

• Purpose: preserves single‑family character; maximum density one single‑family dwelling per one‑half acre (exclusive of ADUs) — § 17.16.010 — .
• Typical permitted uses: single‑family dwellings, accessory structures, country club (where applicable), public parks/playgrounds, town facilities (see the RD‑table in § 17.16.010(B)) — .
• Key dimensional standards that apply everywhere (not unique to RD‑1):
  • Front (street‑line) setback: 25 ft (the "street‑line setback area") — § 17.24.020(A) — .
  • Interior setback: 20 ft — § 17.24.020(C) — .
  • Building envelope/height: envelope starts at grade to 22 ft then slopes at 45° inward to a maximum of 32 ft measured to a warped plane — § 17.28.010 — .
  • Lot coverage / size controls: structural + hardscape generally ≤ 50% of net lot area; structural coverage table varies by lot size (see Chapter 17.32.020(B–C)) — .
• Where it applies: any parcel mapped RD‑1 on the town zoning map — § 17.12.010 and § 17.04.030 — .

RD‑2 — Mixed Residential

• Purpose: intended for townhomes / multifamily on limited town-owned land; minimum density 20 units/acre where applied — § 17.16.010(A)(2) — .
• Typical permitted uses: multifamily housing, public buildings/parks, town facilities, telecommunications structures (see table in § 17.16.010(B)) — .
• Key dimensional standards: base setbacks, height envelope, lot coverage and parking chapters apply as for RD‑1 (see 17.24, 17.28, 17.32, 17.36) — .
• Where it applies: only on parcels mapped RD‑2 — § 17.12.010 — .

RD‑3 — Governmental & Residential Mixed Use

• Purpose: to accommodate town facilities and limited residential units on certain town‑owned land; the code caps the potential number of dwelling units (e.g., maximum of 16 dwelling units on the land zoned in this district) — § 17.16.010(A)(3) — .
• Typical permitted uses: town facilities, public buildings, limited residential, telecommunications, and others as listed in § 17.16.010(B) — .
• Key dimensional standards: the same base development standards apply (setbacks, height envelope, coverage, parking) unless a town council action or specific conditional permit modifies them — see 17.24, 17.28, 17.32, 17.36 — .
• Where it applies: parcels mapped RD‑3 on the zoning map — § 17.12.010 — .

How overlay‑type outcomes are achieved in Hillsborough (practical synthesis)

• Instead of a labeled overlay layer, Hillsborough implements area‑specific controls via the zoning map and targeted rules in Title 17 (for example, the ADU standards in Chapter 17.52 and the building envelope/height rules in Chapter 17.28) — .
• Design and neighborhood fit are handled via the town's design review process and architecture/design board references in several chapters; this is the usual tool for site‑specific character controls that overlays perform elsewhere — see the design review cross‑references in Sections such as 17.20, 17.24 — .
• Parking exceptions or requirements that would commonly be part of an overlay are found in Chapter 17.36 and the ADU chapter; see Hillsborough parking and ADU rules for ministerial exceptions — .
• For historic or special protections, the code references historic inventories and creates specific processes (e.g., ADU exceptions for properties with identified historic resources), which functionally act as overlays for those parcels — see 17.52 (ADUs and historic exceptions) and nonconforming/historic references — .

Most decision‑relevant standards (quick table)

Checklist — what an applicant should confirm before assuming an overlay will apply

• Confirm the parcel's base zone on the official Hillsborough zoning map (zoning map on file with the city clerk) — § 17.04.030 — .
• Check whether the parcel is within RD‑1, RD‑2, or RD‑3 and apply the uses table in § 17.16.010 — .
• Verify applicable setbacks: 25 ft street‑line and 20 ft interior as baseline — § 17.24.020 — .
• Confirm building envelope/height limits (22 ft then 45° slope to 32 ft max) — § 17.28.010 — .
• Check lot‑coverage calculations in Chapter 17.32 before site layout — .
• If proposing or impacted by ADUs, read Chapter 17.52 and the ADU exceptions for historic resources — Hillsborough ADUs — .
• Review design review triggers and process on the town's design review page — verify whether design review or architecture board approval is required — .
• Confirm parking requirements and any ADU parking exceptions in Chapter 17.36 — parking — .
• Ask planning staff whether any parcel‑specific restrictions (map notes, easements, private CC&Rs, or separate ordinances) act like overlays — Verify with the jurisdiction.

Risks & Ambiguities

Plain‑English summary

Hillsborough's zoning code uses base zones (RD‑1, RD‑2, RD‑3) and townwide chapters (setbacks, height envelope, lot coverage, ADU rules, parking, design review) to control development; Title 17 as retrieved does not include a labeled "overlay district" mechanism — parcel‑specific restrictions or special permit requirements are the tools the town uses instead. Confirm parcel status with planning staff before designing a project — Not found in retrieved materials for any overlay chapter — .

Source References

• Hillsborough Zoning Ordinance, Title 17 — Zoning districts (RD‑1, RD‑2, RD‑3): § 17.12.010 —
• Uses permitted and district table: § 17.16.010 —
• Setback locations and distances (street‑line 25 ft; interior 20 ft): § 17.24.020 —
• Building envelope / height limitations (22 ft start; slope to 32 ft max): § 17.28.010 —
• Residential structure size and lot coverage (structural + hardscape ≤ 50% and structural tables): Chapter 17.32 / § 17.32.020 —
• ADU rules / ministerial standards and exceptions: Chapter 17.52 / § 17.52.020 —
• Parking rules and ADU parking exceptions: Chapter 17.36 —
• Zoning map and ordinance short title: § 17.04.030 and § 17.04.020 —
• Nonconforming uses and references to design review/variance processes: Chapter 17.20 and Chapter 17.40 —

(Not found in retrieved materials: any Title 17 section explicitly titled "Overlay District", "Overlay", or "Combining District".)
(If you need the live Municode link or the town's zoning map, ask and I will retrieve the current URLs and map notes or flag any map‑level overlays the town maintains.)

Retrieved passages

• Hillsborough Zoning Code (Title 17) Medium relevance show source text
• Hillsborough Zoning Code (Section 65915) Medium relevance show source text
• Hillsborough Zoning Code (Section 17.16.020) Medium relevance show source text
• Hillsborough Zoning Code (title shall) Medium relevance show source text
• Hillsborough Zoning Code (§ 9) Medium relevance show source text
• Hillsborough Zoning Code (section shall) Medium relevance show source text
• Hillsborough Zoning Code (§ 2) Medium relevance show source text
• CBC § 3 (§ 3) Medium relevance show source text
• Hillsborough Zoning Code (Chapter 2.12) Medium relevance show source text
• California Fire Code Medium relevance show source text
• Hillsborough Zoning Code (Section 801.5) Medium relevance show source text
• Hillsborough Zoning Code (Section 21155) Medium relevance show source text
• California Fire Code Medium relevance show source text
• Hillsborough Zoning Code (section are) Medium relevance show source text
• Hillsborough Zoning Code (section 66333) Medium relevance show source text
• Hillsborough Zoning Code (Section 17.24.030) Medium relevance show source text
• California Fire Code Medium relevance show source text
• Hillsborough Zoning Code (Section 15.24.020) Medium relevance show source text

Cited sections

• Hillsborough Zoning Ordinance, Title 17 — Zoning districts (RD‑1, RD‑2, RD‑3): **§ 17.12.010** — (Title 17)
• Uses permitted and district table: **§ 17.16.010** — (§ 17.16.010)
• Setback locations and distances (street‑line 25 ft; interior 20 ft): **§ 17.24.020** — (§ 17.24.020)
• Building envelope / height limitations (22 ft start; slope to 32 ft max): **§ 17.28.010** — (§ 17.28.010)
• Residential structure size and lot coverage (structural + hardscape ≤ 50% and structural tables): **Chapter 17.32** / **§ 17.32.020** — (Chapter 17.32)
• ADU rules / ministerial standards and exceptions: **Chapter 17.52** / **§ 17.52.020** — (Chapter 17.52)
• Parking rules and ADU parking exceptions: **Chapter 17.36** — (Chapter 17.36)
• Zoning map and ordinance short title: **§ 17.04.030** and **§ 17.04.020** — (§ 17.04.030)
• Nonconforming uses and references to design review/variance processes: **Chapter 17.20** and **Chapter 17.40** — (Chapter 17.20)
• Hillsborough_ZoningCode.md

• Official Hillsborough code library