Contra Costa County — Overlay Districts

Last reviewed: July 6, 2026

Overview

In unincorporated areas of Contra Costa County, “overlay” or “combining” districts layer additional rules on top of base zoning. These districts can change uses, limit density, or impose technical standards where special conditions exist (e.g., hillsides, flood zones, airports). Overlays apply in addition to the base zone shown on the zoning map; when there’s a conflict, the overlay typically governs.

In unincorporated areas, if an overlay’s rule conflicts with the underlying zoning, the overlay’s rule controls. Some overlays expressly preserve the underlying minimum lot size. See § 84-72.408, § 814-2.406, § 84-86.206, § 84-88.204, § 82-28.608, and § 86-4.010

Use this page alongside the County’s broader zoning, development standards, and design review rules. Overlays may also interact with parking, historic preservation, nonconforming uses, and variances and exceptions.

Overlay Districts — District-by-District

SD-1 Slope Density and Hillside Development Combining District (Chapter 814-2)

• Purpose. Protect hillsides and ridgelines; adjust allowed residential density to terrain; minimize grading and erosion; and preserve scenic resources (§ 814-2.204, § 814-2.206) .
• Where it applies. May be combined with any planned unit district or agricultural district located in a General Plan residential area, or with any single-family or two-family residential district (§ 814-2.402) .
• Typical permitted uses. Uses allowed by the underlying district, plus one detached single-family dwelling per legal lot (§ 814-2.404) .
• Key dimensional/technical standards.
  • Density must be computed from the natural average slope using the County’s formula (§ 814-2.602, § 814-2.604) .
  • Cliffs and deep ravines are excluded from density calculations and must be precluded from further residential development (e.g., via scenic easement) (§ 814-2.610) .
  • Priority/Conflict: SD-1 controls where it conflicts, but the minimum lot size remains that of the base zone (§ 814-2.406) .

-T Combining District (Chapter 84-72)

• Purpose. Enable limited, low-intensity business or professional activities to co-exist within residential areas under additional controls.
• Where it applies. May be combined with any residential land use district (§ 84-72.404 intro) .
• Typical permitted uses.
  • By-right: the uses allowed under the combined underlying residential district (§ 84-72.404) .
  • With land use permit: small-scale commercial like art/antique/craft/photography studios, answering services, and professional offices for architects, attorneys, accountants, or engineers (§ 84-72.406) .
• Key dimensional/technical standards.
  • Priority/Conflict: -T controls over the base district, except that minimum lot size stays the same as the underlying district (§ 84-72.408) .
  • Rezoning to -T can be processed concurrently with a land use permit (§ 84-72.604) .

-K Kensington Combining District (Chapter 84-74)

• Purpose. Apply tailored regulations to the Kensington area to protect views, light/solar access, privacy, parking, neighborhood noise levels, and compatibility of bulk and scale (§ 84-74.204) .
• Where it applies. All land within a district combined with the Kensington (-K) designation (§ 84-74.202) .
• Typical permitted uses. Not found in retrieved materials.
• Key dimensional/technical standards. Not found in retrieved materials.

-CE Cannabis Exclusion Combining District (Chapter 84-86)

• Purpose. Categorically exclude commercial cannabis activities within mapped communities/areas of the county (§ 84-86.202, § 84-86.212) .
• Where it applies. All property in all zoning districts within designated unincorporated communities/areas, including Acalanes Ridge, Alamo, Bethel Island, Blackhawk, Bollinger Canyon, Contra Costa Centre, Knightsen, Sandmound Slough, and Saranap (§ 84-86.204) .
• Typical permitted uses. All uses allowed in the underlying zoning district remain allowed (§ 84-86.210) .
• Key dimensional/technical standards.
  • Prohibits commercial cannabis activities regardless of underlying district (§ 84-86.212) .
  • Priority/Conflict: -CE controls over the base district (§ 84-86.206) .

-SG Solar Energy Generation Combining District (Chapter 84-88; cross-refs in Chapter 88-30)

• Purpose. Allow commercial solar facilities on designated agricultural lands with added environmental and end-of-life standards (§ 84-88.202, § 84-88.404; § 88-30.614, § 88-30.616) .
• Where it applies. Only when combined with agricultural districts A-2, A-3, A-20, A-40, or A-80 (§ 84-88.202) .
• Typical permitted uses.
  • All uses allowed in the underlying ag zone continue (§ 84-88.402) .
  • Commercial solar energy facilities require a land use permit and must meet the Chapter 88-30 standards (§ 84-88.404) .
• Key dimensional/technical standards.
  • Habitat avoidance: keep commercial arrays at least 75 ft from creeks and 50 ft from other aquatic habitat unless the County issues a land use permit with protective findings (§ 88-30.614) .
  • Site restoration: removal to three feet below finished grade and a restoration security/bond are required (§ 88-30.616) .
  • Priority/Conflict: -SG controls over base zoning (§ 84-88.204) .

Floodplain/Flood Hazard Overlay (Article 82-28; FEMA FIS and State flood laws)

• Purpose. Minimize flood risk and qualify the County for the National Flood Insurance Program; restrict hazardous uses and require flood damage reduction standards (§ 82-28.206, § 82-28.208) .
• Where it applies. All land in a “flood hazard zone” within the Sacramento–San Joaquin Valley portion of unincorporated County; mapping on file with the County (§ 82-28.1402, § 82-28.1404) .
• Typical permitted uses. Governed by base zoning, but development must comply with floodplain standards (§ 82-28.606) .
• Key dimensional/technical standards.
  • Areas of Special Flood Hazard per FEMA’s Flood Insurance Study for Unincorporated Areas, with freeboard: 2 ft in the Bay-Delta Estuarine Region; 1 ft elsewhere (§ 82-28.604) .
  • Variances are rare and subject to detailed hardship and safety criteria (§ 82-28.1202, § 82-28.1204) .
  • “Greater restriction prevails” rule with other regulations (§ 82-28.608) .

Airport Land Use and Height Overlay (Division 86-4—Buchanan Field)

• Purpose. Protect airspace and public safety in the vicinity of Buchanan Field with height and land-use limits (§ 86-4.012, § 86-4.014, § 86-4.016) .
• Where it applies. Outside the airport boundaries and within ~2 miles of the landing area, per the adopted Airport Zoning Plan map (§ 86-4.012) .
• Typical permitted uses. Governed by base zoning; overlay restricts hazardous uses (e.g., radio interference, glare, wildlife attractants) (§ 86-4.016) .
• Key dimensional/technical standards.
  • Height limits vary by zone. Example: In Approach Zones 1–4, max height is 20 ft at 1,000 ft from runway ends; increases by 5 ft for every additional 200 ft, capped at 150 ft. Other approach/turning/transition zones have mapped limits (§ 86-4.014) .
  • “More stringent rule governs” for conflicts (§ 86-4.010) .

Overlay Quick Reference

Practical Notes

• Overlays stack: A parcel can be in, for example, the SD-1 and the Floodplain overlay; you must meet both sets of rules. Check the County’s zoning & planning overview and parcel mapping with staff for confirmation. Verify with the jurisdiction for parcel-specific applicability.
• Overlays often trigger additional review. For instance, commercial solar in -SG needs a land use permit with environmental safeguards; expect coordination with landscaping and screening and potential design review conditions (§ 84-88.404; § 88-30.614, § 88-30.616) .
• State laws still apply. For example, California Building Standards Code and California ADU law may constrain local discretion even inside overlays. Always reconcile these with County rules.

Checklist

• Confirm your parcel’s base zone and all mapped overlays in unincorporated areas (Zoning).
• Read the overlay’s purpose, applicability, and priority/conflict rules (e.g., SD-1 § 814-2.406; -T § 84-72.408; -SG § 84-88.204; -CE § 84-86.206) .
• Identify allowed uses and whether a land use permit is required (e.g., -T § 84-72.406; -SG § 84-88.404) .
• If in SD-1, run the average slope calculation and check the density table; exclude cliffs/ravines as required (§ 814-2.604, § 814-2.610) .
• If in a Flood Hazard area, verify FEMA FIS panel, freeboard, and any floodway limits (§ 82-28.604, § 82-28.606) .
• If near Buchanan Field, measure proposed structure heights against mapped approach/turning/transition zone limits (§ 86-4.014) .
• Cross-check unrelated standards that still apply (setbacks, height, parking, signage) and whether design review is triggered by your proposal.
• If an overlay renders your existing use/structure out of compliance, review nonconforming uses procedures. Consider variances and exceptions; note Flood variances are unusually strict (§ 82-28.1202, § 82-28.1204) .

Risks & Ambiguities

Plain-English Summary

If your property in unincorporated Contra Costa County sits in a mapped overlay, that layer can change what you can build and how. Hillside parcels face slope-based density in SD-1; flood zones require extra elevation; properties near Buchanan Field face height caps; certain communities bar commercial cannabis; agricultural lands with -SG can host commercial solar only with strict environmental and restoration standards. Start by confirming every overlay on your parcel, then design to the most restrictive rule.

Source References

• § 814-2.202, § 814-2.204, § 814-2.206, § 814-2.402, § 814-2.404, § 814-2.406, § 814-2.602, § 814-2.604, § 814-2.610, § 814-2.612
• § 84-72.404, § 84-72.406, § 84-72.408, § 84-72.604
• § 84-74.202, § 84-74.204
• § 84-86.202, § 84-86.204, § 84-86.206, § 84-86.210, § 84-86.212
• § 84-88.202, § 84-88.204, § 84-88.206, § 84-88.402, § 84-88.404; § 88-30.614, § 88-30.616
• § 82-28.604, § 82-28.606, § 82-28.608, § 82-28.1202, § 82-28.1204, § 82-28.1402, § 82-28.1404, § 82-28.1406, § 82-28.1408
• § 86-4.010, § 86-4.012, § 86-4.014, § 86-4.016

Information Gaps

• Detailed development standards for the -K Kensington combining district: Not found in retrieved materials.
• Any additional overlay districts beyond those listed here: Not found in retrieved materials.

Retrieved passages

• Contra Costa County Zoning Code (chapter and) Medium relevance show source text
• Contra Costa County Zoning Code (§ III) Medium relevance show source text
• Contra Costa County Zoning Code (Chapter 814-2) Medium relevance show source text
• Contra Costa County Zoning Code (§ 4) Medium relevance show source text
• Contra Costa County Zoning Code (article are) Medium relevance show source text
• Contra Costa County Zoning Code (article are) Medium relevance show source text
• Contra Costa County Zoning Code (Section 82-28.1202) Medium relevance show source text
• Contra Costa County Zoning Code (Article 84-84.4.) Medium relevance show source text

Cited sections

• § 814-2.202, § 814-2.204, § 814-2.206, § 814-2.402, § 814-2.404, § 814-2.406, § 814-2.602, § 814-2.604, § 814-2.610, § 814-2.612 (§ 814-2.202)
• § 84-72.404, § 84-72.406, § 84-72.408, § 84-72.604 (§ 84-72.404)
• § 84-74.202, § 84-74.204 (§ 84-74.202)
• § 84-86.202, § 84-86.204, § 84-86.206, § 84-86.210, § 84-86.212 (§ 84-86.202)
• § 84-88.202, § 84-88.204, § 84-88.206, § 84-88.402, § 84-88.404; § 88-30.614, § 88-30.616 (§ 84-88.202)
• § 82-28.604, § 82-28.606, § 82-28.608, § 82-28.1202, § 82-28.1204, § 82-28.1402, § 82-28.1404, § 82-28.1406, § 82-28.1408 (§ 82-28.604)
• § 86-4.010, § 86-4.012, § 86-4.014, § 86-4.016 (§ 86-4.010)
• ContraCostaCounty_ZoningCode.md

• Official Contra Costa County code library