Walnut — Overlay Districts

Last reviewed: July 3, 2026

Overview

Walnut’s municipal code implements two principal overlay classifications: the R-1 Rural Overlay (an "A" overlay applied to parcels with horse/animal and rural-lifestyle rules) and the Mixed Use / Housing Opportunity Overlay (MU/HOO) (three mapped MU/HOO areas designed to enable higher-density and mixed-use housing). The code explains where each overlay is mapped, what extra uses or incentives the overlay adds to the underlying base zone, and how new projects in the overlay are reviewed and regulated (see § 6.16.010 and § 6.20.010 – § 6.20.070) . For basic navigation to Walnut’s planning pages see the city overview page on Walnut zoning & planning overview.

R-1 Rural Overlay (the "A" overlay)

• Purpose: The R-1 Rural Overlay is created to allow and regulate the keeping of horses and similar domestic animals and to preserve rural/recreational uses in specified areas. The overlay is shown on the official zoning map with an "A" overlay and its rules take precedence over the base zone where they conflict (§ 6.16.010) .
• Typical permitted uses: household pets and, on sufficiently large lots, horses, donkeys, bovines and similar animals as accessory uses; accessory structures for animals are allowed with review (§ 6.16.020, § 6.16.040) .
• Key dimensional/process rules:
  • Animal allowances are tied to lot area (for example, one horse on lots ≥ 13,500 sq ft with additional animals allowed per larger lot thresholds) — see § 6.16.020(A) for the numeric thresholds and counts .
  • Accessory buildings for animals require Development Review Board approval and must meet submittal requirements (site plan, material/appearance notes) and cannot be closer than 35 ft to a habitable building (§ 6.16.040.D) .
  • The overlay’s additional requirements override the base zone where inconsistent (§ 6.16.010.B) .
• Where it applies: parcels specifically designated by City Council and marked on the zoning map as the "A" overlay (verify the map on file with the City Clerk) (§ 6.16.010.B, and the Zoning Map rules in § 6.08.040) .

Mixed Use / Housing Opportunity Overlay — MU/HOO (three mapped areas)

• Purpose: The MU/HOO overlay is intended to create opportunities for higher-density residential and mixed-use development in targeted areas to help meet the City’s housing obligations and to encourage affordable units and cohesive mixed-use nodes (§ 6.20.010) .
• How it works: MU/HOO is an additional zoning layer appended to the base zone. It does not eliminate underlying allowable uses but creates additional permitted uses, density ranges, and incentives; many development standards are expected to be set in a site-specific Specific Plan adopted by the City Council (§ 6.20.020, § 6.20.050) .

District-by-district breakdown (per § 6.20.020 / § 6.20.030):

• MU/HOO-1 (West Valley Specific Plan area)

  • Permitted uses: any use allowed by the underlying C‑1 and C‑3 zones plus multifamily residential where parcels meet size and specific-plan conditions (§ 6.20.030.A) .
  • Density: on parcels ≥ 1 acre: minimum 12 du/acre and maximum 36 du/acre; parcels < 1 acre: maximum 20 du/acre (§ 6.20.030.A.2) .
  • Standards & process: multifamily or mixed-use projects require a specific plan to establish setbacks, heights, parking ratios, architectural standards and affordability ratios; site plan and architectural review apply (§ 6.20.050, § 6.20.070) .

• MU/HOO-2 (Cornerstone Specific Plan area)

  • Permitted uses: any C‑3 uses plus integrated multifamily and retail/commercial; the overlay requires at least 2 acres of retail/commercial in the project mix to ensure mixed-use character (§ 6.20.030.B) .
  • Density: multifamily minimum 12 du/acre, maximum 28 du/acre (subject to specific plan); parcels < 1 acre capped at 20 du/acre (§ 6.20.030.B.2) .
  • Standards & process: specific plan required; incentives available (density bonus, relaxed standards) per § 6.20.060 .

• MU/HOO-3 (The Terraces at Walnut Specific Plan area)

  • Permitted uses: three sub-areas: Area 1 — uses permitted in R‑1 with a 16,800 sq ft minimum lot size; Area 2 — multifamily uses comparable to R‑3 subject to specific plan; Area 3 — retail/service commercial subject to specific-plan design standards (§ 6.20.030.C) .
  • Density: Area 2 multifamily minimum 12 du/acre up to 36 du/acre (subject to specific plan); <1 acre parcels still limited to 20 du/acre (§ 6.20.030.C.2) .
  • Standards & process: same specific-plan-driven approach; plan may reference adopted Specific Plan No. 2, No. 3 or No. 4 and objective design standards (§ 6.20.070) .

Overlay incentives and review

• Incentives permitted by the MU/HOO overlay include density bonuses, reduced/relaxed development standards (e.g., parking reductions, setback relaxations, height increases), financial incentives (fee waivers or reductions), and expedited processing for qualifying affordable projects (§ 6.20.060) .
• Projects that change land use or constitute new construction in MU/HOO are reviewed by the Planning Commission and are subject to site plan and architectural review under Chapter 6.84; specific plans may impose additional objective design standards (§ 6.20.070) . For City design-review procedures see Walnut Design Review.

Table — Quick reference: overlay decision-relevant standards and uses

Practical interactions with other code topics

• Development standards for MU/HOO projects are frequently established in a site-specific Specific Plan; confirm the applicable Specific Plan and its adopted standards before preparing plans (§ 6.20.050) . See the city’s Walnut Development Standards page when preparing submittals.
• MU/HOO projects commonly seek density bonuses or parking reductions — the overlay expressly contemplates density bonus incentives (cross-reference Chapter 6.100 for density-bonus mechanics) (§ 6.20.060) . Check Walnut Parking rules when estimating required stalls.
• New construction inside MU/HOO is subject to site plan/architectural review under Chapter 6.84 — applicants should plan for concurrent review and expect objective design standards from adopted specific plans (§ 6.20.070) . For process details consult Walnut Design Review.
• Interaction with ADU rules: the ADU chapter explains how ADU standards (setbacks, lot coverage, FAR, etc.) apply and lists higher lot-coverage allowances for MU/HOO areas for ADU calculations (for example, MU/HOO-1 ADU lot coverage 80%) — see the ADU development-standards section and the ADU page for local ADU rules and state law context (§ 6.08.210 and ADU subsections) . For the state building code interface see California Building Standards Code and for local ADU rules see Walnut ADUs.

Checklist

• Confirm overlay mapping for the property on the official zoning map (zoning map on file with the City Clerk) (§ 6.08.040) .
• If inside the R-1 Rural Overlay, demonstrate lot area thresholds and animal/accessory structure compliance and include animal-structure siting per § 6.16.020 / § 6.16.040 .
• If inside MU/HOO, determine which MU/HOO sub-area applies (MU/HOO-1, MU/HOO-2, MU/HOO-3) and use the applicable density ranges and required Specific Plan items (§ 6.20.020, § 6.20.030, § 6.20.050) .
• Prepare a Specific Plan (or confirm which adopted Specific Plan applies) where required; the Specific Plan must set setbacks, heights, parking ratios, affordability ratios where noted (§ 6.20.050) .
• Prepare materials for site plan & architectural review (Chapter 6.84) and expect Planning Commission review for land‑use changes in MU/HOO (§ 6.20.070) .
• If requesting incentives (density bonus, parking reductions), document affordable-unit commitments and reference Chapter 6.100 for bonus calculations (§ 6.20.060) .
• For ADU proposals, confirm overlay-related lot-coverage and setback rules in the ADU section; ADU ministerial processing rules and time limits apply (§ 6.08.210 and ADU subsections) .
• Verify required public notices, any applicable conditional-use/permit requirements, and whether other approvals (e.g., specific-plan adoption by City Council) are needed — Verify with the jurisdiction.

Risks & Ambiguities

Plain-English Summary

Walnut uses two mapped overlays: the R‑1 Rural Overlay (A) to protect rural/animal uses on certain large lots, and the MU/HOO overlay (three mapped MU/HOO areas) to permit denser housing and mixed-use development where a Specific Plan establishes detailed standards. MU/HOO projects can get density and development incentives but must follow the specific-plan and design-review process described in the code (verify exact map coverage and plan details with the City) (§ 6.16.010, § 6.20.010–§ 6.20.070) .

Source References

• Walnut Municipal Code — R‑1 Rural Overlay (A overlay): § 6.16.010, § 6.16.020, § 6.16.040 .
• Walnut Municipal Code — Mixed Use / Housing Opportunity Overlay (MU/HOO): § 6.20.010, § 6.20.020, § 6.20.030, § 6.20.040, § 6.20.050, § 6.20.060, § 6.20.070 .
• Walnut Municipal Code — Zoning map and map interpretation: § 6.08.040 (zoning map) .
• Walnut Municipal Code — ADU/Accessory Housing (overlay interactions with ADU rules, development standards): § 6.08.210 and the ADU development-standards subsections referenced in the ADU chapter (lot coverage, setbacks, ministerial timing) .
• For city practice pages referenced in text: Walnut zoning & planning overview, Walnut Zoning, Walnut Development Standards, Walnut Parking, Walnut Design Review, Walnut ADUs, California Building Standards Code.

Retrieved passages

• Walnut Zoning Code (§ 6.16.040.) High relevance show source text
• Walnut Zoning Code (§ 6.20.020.) High relevance show source text
• Walnut Zoning Code (§ 6.20.040.) High relevance show source text
• Walnut Zoning Code (§ 6.20.040.) Medium relevance show source text
• Walnut Zoning Code Medium relevance show source text
• Walnut Zoning Code Medium relevance show source text
• Walnut Zoning Code (Chapter 2-5) Medium relevance show source text
• Walnut Zoning Code (§ 6.12.060.) Medium relevance show source text
• CBC § 310 (section may) Medium relevance show source text
• Walnut Zoning Code Medium relevance show source text
• CFC § 150 Medium relevance show source text
• Walnut Zoning Code Medium relevance show source text
• Walnut Zoning Code Medium relevance show source text
• Walnut Zoning Code Medium relevance show source text

Cited sections

• Walnut Municipal Code — **R‑1 Rural Overlay (A overlay)**: **§ 6.16.010**, **§ 6.16.020**, **§ 6.16.040** . (§ 6.16.010)
• Walnut Municipal Code — **Mixed Use / Housing Opportunity Overlay (MU/HOO)**: **§ 6.20.010**, **§ 6.20.020**, **§ 6.20.030**, **§ 6.20.040**, **§ 6.20.050**, **§ 6.20.060**, **§ 6.20.070** . (§ 6.20.010)
• Walnut Municipal Code — **Zoning map and map interpretation**: **§ 6.08.040** (zoning map) . (§ 6.08.040)
• Walnut Municipal Code — **ADU/Accessory Housing** (overlay interactions with ADU rules, development standards): **§ 6.08.210** and the ADU development-standards subsections referenced in the ADU chapter (lot coverage, setbacks, ministerial timing) . (§ 6.08.210)
• For city practice pages referenced in text: Walnut zoning & planning overview, Walnut Zoning, Walnut Development Standards, Walnut Parking, Walnut Design Review, Walnut ADUs, California Building Standards Code.
• Walnut_ZoningCode.md

• Official Walnut code library