Union City — Overlay Districts

Last reviewed: July 2, 2026

Overview

Union City's Zoning Code (Title 18) uses overlay and combining districts to add site- or policy-specific rules on top of a property's base zoning. Common overlays in the code are the Housing Element (HE) Overlay Zone, the Landmark and Historic Preservation (LHP) Overlay Zone, the Hillside Combining (-H) District, and the Civic Center Design Control District (CCDCD); each modifies base district regulations and, in some cases, imposes additional review requirements. For basic permit pathways and how overlays interact with base zoning and reviews, start with the City's zoning and development standards guidance (first natural mentions are linked). All statements below are drawn from the Union City Zoning Code (Title 18) as cited.

How to read this page

• Each district subsection names the chapter and gives the ordinance range that controls that overlay. Where the code defers to the base zone, the text says so and cites the applicable chapters.
• When the code text is not available in the retrieved materials for a detail you ask about, I flag it as "Not found in retrieved materials" and recommend "Verify with the jurisdiction."

Chapter-by-chapter overlay breakdown

Housing Element (HE) Overlay Zone

• Code reference: § 18.116.010 – § 18.116.030
• Purpose: Implement the City's adopted Housing Element and ensure certain sites allow a minimum 20 dwelling units per acre (i.e., meet Government Code requirements for sites demonstrating capacity for very low / low income households). § 18.116.010 – § 18.116.030 describes the overlay's purpose and effect.
• Typical permitted uses: Uses are those allowed by the site's base zoning district; the HE overlay does not create new use categories but modifies density/site-area rules that affect residential development capacity. The chapter explicitly applies the Title 18 base regulations "augmented by the maximum site area per dwelling unit regulations prescribed in this chapter." § 18.116.010 – § 18.116.030
• Key dimensional standard (decision-relevant):
  • Sites in the HE overlay that have an RM 1500 base zoning must allow 1,450 to 2,178 square feet of gross site area per dwelling unit, corresponding to 20–30 dwelling units per acre. The HE overlay therefore sets a maximum site area per unit of 2,178 sq ft where RM 1500 applies, superseding conflicting base provisions. § 18.116.010 – § 18.116.030; underlying RM table reference: § 18.32.060.
• Where it applies: On parcels identified for rezoning/implementation under the City's Housing Element (applied to specific sites; check the City map/rezoning ordinance). The chapter language makes HE a site-specific overlay that changes density/site-area metrics. § 18.116.010 – § 18.116.030
• Practical guidance: If you propose residential density increases, compare the site's base district (e.g., RM 1500) rules in § 18.32.060 with the HE overlay maximum 2,178 sq ft/unit in § 18.116; the HE overlay controls in conflict.

Landmark and Historic Preservation (LHP) Overlay Zone

• Code reference: § 18.106.100 – § 18.106.420
• Purpose: Preserve and manage changes to landmarks, historic properties, and historic districts by layering preservation policy and review requirements on top of the base zoning. § 18.106 sets the LHP overlay as an additional regulatory layer.
• Typical permitted uses: The LHP overlay generally preserves the base district uses (uses permitted in the underlying zoning remain allowed) but makes many exterior changes subject to additional review. The code explains that eligible projects (for example, second-story additions, exterior remodels, and accessory structures above certain sizes) are processed with site review and historic review criteria. See administrative-review references for specific project types. § 18.106 and the administrative review chapters.
• Key standards/controls:
  • The overlay imposes additional documentation, design, and review requirements for alterations within the overlay; many projects that are “minor” in other districts still require review if they affect historic resources (see site and administrative review rules). See Chapter 18.76 — Site Development Review for the procedure that applies to projects in historic areas. § 18.106.100 – § 18.106.420; § 18.76.010 – § 18.76.110.
• Where it applies: To properties and districts formally designated as landmarks or historic districts by the City (map/list maintained by the City). The code treats the overlay as a geographic designation added to parcels to trigger preservation rules. § 18.106.100 – § 18.106.420
• Practical guidance: Expect required design-level materials, and that exterior modifications may trigger site development review or historic-preservation review. Consult the City's historic preservation guidance and the Site Development Review procedures in § 18.76.

Hillside Combining (-H) District

• Code reference: § 18.96.010 – § 18.96.080
• Purpose: Protect scenic, geotechnical, and open-space values of the City's Hillside area and ensure development responds to topography, seismic safety, drainage, and visual sensitivity. § 18.96.010 – § 18.96.080 sets the combining district's purpose and application.
• Typical permitted uses: Uses are those of the base residential districts when combined with the Hillside -H overlay, but any development in the -H district is subject to stricter siting, grading, and review rules; the code requires conditional use/permit or site development review for proposed development. § 18.96 states that base-district uses remain, but approvals are conditioned by the combining district provisions.
• Key dimensional/decision standards:
  • The Hillside area is defined geographically as "all portions of Union City north and east of Mission Boulevard" (the code gives that boundary) and imposes limits and procedures for grading, slope modification, and road grades. The -H regulations control conflicts with base district rules (the combining district rules prevail on conflict). § 18.96.010 – § 18.96.080.
  • Applications in the -H District require the use-permit and site development review procedures per Chapters 18.56 and 18.76, except where administrative review applies (see 18.72). § 18.96.
• Where it applies: To the City's Hillside area (geographic boundary described in the chapter). § 18.96.010 – § 18.96.080
• Practical guidance: For Hillside parcels expect mandatory geotechnical and visual analyses, stricter grading limits and potential requirements for scenic easements/transfer of development rights. See the site-review rules in § 18.76 for required submittals.

Civic Center Design Control District (CCDCD)

• Code reference: § 18.78.010 – § 18.78.110
• Purpose: Protect the public investment and ensure high-quality urban design around the Civic Center complex; the CCDCD layers design-control requirements on top of whatever base zoning exists in the area. § 18.78.010 – § 18.78.110
• Typical permitted uses: The code says "Uses permitted in any zoning district located within the CCDCD shall be permitted." In other words, the CCDCD does not change uses but adds design/submittal requirements and design standards. § 18.78.010 – § 18.78.110
• Key standards/controls:
  • CCDCD regulations are "in addition to" the underlying zone rules; applicants must submit additional materials (area map, building materials, signage, landscaping, fencing) and follow the underlying review procedures. § 18.78.010 – § 18.78.110.
  • Parking and screening requirements for parking/loading in the CCDCD refer to underlying rules (see off-street parking rules). For parking details consult the City's parking guidance and § 18.36/18.28 references.
• Where it applies: The geographic area immediately surrounding the Civic Center complex as defined in the CCDCD chapter; overlay maps/section references are in the chapter. § 18.78.010 – § 18.78.110
• Practical guidance: Expect added design documentation and stricter façade/landscaping/signage submittals; the approval process follows the underlying zone’s procedure augmented by CCDCD findings. § 18.78.010 – § 18.78.110.

Quick comparison table — key decision-relevant overlay standards

Checklist

• Confirm whether the parcel is inside an overlay or combining district (check the City zoning map / verify with planning staff). Verify any geographic descriptions in § 18.96 (Hillside) or the map references in the relevant overlay chapter. § 18.96.010 – § 18.96.080; § 18.116.010 – § 18.116.030.
• Compare overlay rules to the parcel’s base zoning — if they conflict, the overlay chapter controls (the HE overlay explicitly says its provisions take precedence). § 18.116.010 – § 18.116.030.
• Determine required discretionary procedures: administrative site review (Chapter 18.72) or full site development review (§ 18.76.010 – § 18.76.110) or use/variance permits (Chapters 18.56, 18.60, 18.52 for appeals).
• For historic properties (LHP), assemble historic/resource documentation and plan for additional design-level submittals; follow the LHP chapter's specific submittal/criteria. § 18.106.100 – § 18.106.420.
• For Hillside sites, include geotechnical, grading, and visual analyses; check road-grade and slope limits cited in § 18.96. § 18.96.010 – § 18.96.080.
• Confirm parking and loading standards referenced by the overlay (parking standards are cross-referenced in commercial and overlay chapters); consult the City's parking resource and § 18.28 / 18.36.
• If proposing an ADU, check accessory dwelling unit provisions (Chapter 18.34) and whether the overlay imposes any additional historic or design constraints; see ADUs and the code references where the overlay calls out ADU rules. Not every overlay changes ADU rules — verify with the jurisdiction.

Risks & Ambiguities

Plain-English Summary

Union City’s overlays (for housing implementation, historic preservation, hillsides, Civic Center design, etc.) do not usually change what you can use your land for; they add or change how dense you may be and impose extra design, documentation, or review requirements. The HE overlay is the clearest example: it forces certain parcels to allow 20–30 du/acre (i.e., 1,450–2,178 sq ft per unit where RM 1500 applies), while LHP and -H add design, historic, and environmental/grade controls — read the overlay chapter and then compare to the parcel’s base zone before preparing plans. § 18.116; § 18.106; § 18.96.

Source References

• Union City Zoning Code — Title 18 (general): § 18.04.010 – § 18.04.210 — Union City Zoning Code (Title 18).
• Housing Element (HE) Overlay Zone: § 18.116.010 – § 18.116.030 (purpose and site-area density rules; HE takes precedence on conflict).
• Landmark and Historic Preservation (LHP) Overlay Zone: § 18.106.100 – § 18.106.420 (historic overlay rules and review).
• Hillside Combining (-H) District: § 18.96.010 – § 18.96.080 (geographic boundary and hillside development controls).
• Civic Center Design Control District (CCDCD): § 18.78.010 – § 18.78.110 (additional design submittals and findings).
• Site Development Review (procedures): § 18.76.010 – § 18.76.110 (applies to projects, including overlays; submittal/fee/approval rules).
• Cross-references used in the code for base zoning and RM tables: § 18.32.060 (RM site-area per dwelling unit table; HE overlays reference this table).

For the City’s general planning and zoning material, consult the Union City zoning & planning overview: Union City zoning & planning overview. For design or aesthetic review requirements see the City’s design review page and the City’s historic preservation resource. For ADU-related ministerial standards consult ADUs and the California Building Standards Code for building-related rules.

Retrieved passages

• CBC § 4 (§ 4) High relevance show source text
• Union City Zoning Code (§ 2) High relevance show source text
• Union City Zoning Code (chapter a) High relevance show source text
• Union City Zoning Code (§ 2) High relevance show source text
• Union City Zoning Code (§ 2) High relevance show source text
• Union City Zoning Code (§ 2) Medium relevance show source text
• Union City Zoning Code (Chapter 18.56) Medium relevance show source text
• Union City Zoning Code (§ 4) Medium relevance show source text
• Union City Zoning Code (§ 2) High relevance show source text
• Union City Zoning Code (§ 5) High relevance show source text
• Union City Zoning Code (Chapter 18.40) High relevance show source text
• Union City Zoning Code (Chapter 18.112) Medium relevance show source text
• Union City Zoning Code (§ 4) Medium relevance show source text
• Union City Zoning Code (§ 2) Medium relevance show source text
• Union City Zoning Code (§ 2) Medium relevance show source text
• Union City Zoning Code (Title 18) Medium relevance show source text
• Union City Zoning Code (§ 2) Medium relevance show source text
• Union City Zoning Code (Chapter 18.30.) Medium relevance show source text

Cited sections

• Union City Zoning Code — Title 18 (general): **§ 18.04.010 – § 18.04.210** — Union City Zoning Code (Title 18). (Title 18)
• **Housing Element (HE) Overlay Zone**: **§ 18.116.010 – § 18.116.030** (purpose and site-area density rules; HE takes precedence on conflict). (§ 18.116.010)
• **Landmark and Historic Preservation (LHP) Overlay Zone**: **§ 18.106.100 – § 18.106.420** (historic overlay rules and review). (§ 18.106.100)
• **Hillside Combining (-H) District**: **§ 18.96.010 – § 18.96.080** (geographic boundary and hillside development controls). (§ 18.96.010)
• **Civic Center Design Control District (CCDCD)**: **§ 18.78.010 – § 18.78.110** (additional design submittals and findings). (§ 18.78.010)
• **Site Development Review (procedures)**: **§ 18.76.010 – § 18.76.110** (applies to projects, including overlays; submittal/fee/approval rules). (§ 18.76.010)
• Cross-references used in the code for base zoning and RM tables: **§ 18.32.060** (RM site-area per dwelling unit table; HE overlays reference this table). (§ 18.32.060)
• UnionCity_ZoningCode.md

• Official Union City code library