Glenn County — Overlay Districts

Last reviewed: July 3, 2026

Overview

Glenn County treats overlay rules as combining districts in its Unified Development Code (Title 15). The two county-level overlays used across the unincorporated areas are the Flood Plain Management Zone (FP) and the Airport Hazard Zone (AVH); both layer extra standards onto the underlying base zone to protect public safety and infrastructure. The code that creates and controls these overlays is in Title 15 — Unified Development Code (the county zoning code) and the combining-district list is in § 15.30.020.

(Links: the Glenn County Zoning rules are the base; read the county Development Standards for dimensional requirements that interact with overlays. If your project touches parking, setbacks, design review, or variances see the county pages for Parking, Design Review, Nonconforming Uses, and Variances and Exceptions. For building-safety specifics consult the California Building Standards Code and for ADU-specific state rules consult California ADU law.)

How Glenn County labels overlays (official name)

• The county calls overlays “combining districts” in the Unified Development Code; the combining-district group is Division 15-3 Part 3 (see § 15.30.020). The combining/overlay districts in that list include FP and AVH.

District-by-district breakdown

FP — Flood Plain Management Zone (combining district)

• Purpose: The FP overlay aims to reduce flood losses, protect life and property, and implement the FEMA Flood Insurance Study and maps as minimum standards for special flood hazard areas (§ 15.54.010, § 15.54.040).
• Where it applies: The overlay applies to all areas of special flood hazard shown in the county’s adopted Flood Insurance Study and Flood Insurance Rate Maps (FIRMs) — the maps and study are adopted by reference and kept on file at the planning authority (§ 15.54.040, § 15.54.050).
• Typical permitted uses / approach: The FP chapter does not simply list “permitted uses” like a base zone; instead it restricts, conditions, or requires mitigation for development within the floodplain. Uses that are permitted must comply with the chapter’s required construction and elevation standards; some low‑risk uses may be allowed where they meet the development-permit rules in § 15.54.070. The overlay’s method is regulatory (limit hazardous uses, require floodproofing and elevation) rather than creating a separate use table (§ 15.54.030, § 15.54.070) .
• Key dimensional/technical standards to expect:
  • Development permit required before any construction in mapped special flood hazard areas (§ 15.54.070) — application must show elevations, foundation details and certifications.
  • Lowest floor elevation / floodproofing standards for new or substantially improved structures are set in § 15.54.100 (elevation certificates, floodproofing certifications, and special rules for Zone AO).
  • Subdivision and manufactured home layout standards are in § 15.54.120 and § 15.54.130 (expect minimum elevation and pad/anchoring requirements).
  • Floodway encroachment rules: developments that would increase base‑flood elevations or affect carrying capacity are restricted; technical certification is required and variances are tightly controlled (§ 15.54.160, § 15.54.180).
• Practical guidance: If a parcel falls within the FP overlay the applicant must provide elevation data, demonstrate compliance with the lowest-floor/floodproofing standards, and may need a Letter of Map Revision (LOMR) submission to FEMA if the project alters a watercourse (§ 15.54.090, § 15.54.070).

AVH — Airport Hazard Zone (combining district)

• Purpose: The AVH overlay protects airport operations and nearby properties by preventing “airport hazards” that could endanger aircraft or people; it is adopted to conform to FAA standards and state law and specifically names Glenn County airports (Willows and Orland) (§ 15.55.010).
• How it layers on parcels: The AVH is explicitly a zone “which may be combined with any other zone in this title,” meaning its controls sit on top of the underlying base zone (e.g., AE, R-1, C, etc.) and add height/use restrictions where airport surfaces project over land (§ 15.55.010).
• Zones / surfaces: The overlay divides airport-influence land into approach, transitional, horizontal, and conical zones that match the FAR Part 77 surfaces; the official airport zoning maps and approach maps are kept on file and made part of the chapter (§ 15.55.030).
• Typical permitted uses / restrictions:
  • Uses allowed on the parcel remain governed by the underlying zone, but the AVH layer can ban or condition uses that create hazards (tall structures, glare, smoke, dust, emissions, concentrated populations, or uses that attract birds). Precise use-limits are in § 15.55.050 (see the code for the full list).
• Key dimensional/technical standards:
  • Height limits: the overlay imposes maximum heights measured from airport reference elevation and according to surface slopes; e.g., at Willows Airport the horizontal and conical limits are 150 ft and approach slopes use 34:1 or 20:1 depending on runway — more detail is in § 15.55.040.
  • Variances & nonconforming: the AVH chapter contains procedures and criteria for variances and for handling existing nonconforming uses/structures in § 15.55.060 – § 15.55.070.
• Where it applies: The ordinance names the Willows and Orland airports and requires the airport zoning maps to be maintained and used in application review; any parcel within those mapped surfaces is subject to the AVH overlay rules (§ 15.55.010, § 15.55.030).

Quick decision table — most decision‑relevant overlay rules

Checklist

• Confirm whether your parcel is inside an overlay on the official county zoning / special zone maps (verify maps on file with the planning authority) — § 15.30.020.
• If in FP, obtain a development permit for any construction; provide elevation data, foundation design, lowest‑floor elevations, and required certifications (§ 15.54.070, § 15.54.100) .
• If in FP, check whether your project requires a LOMR or other FEMA filing when altering watercourses; plan for the county’s requirement to submit technical data (§ 15.54.090, § 15.54.040) .
• If in AVH, confirm applicable airport surface (approach, conical, etc.) and the height limit that applies to your lot; measure heights relative to the airport reference elevation listed in § 15.55.040 .
• Confirm whether proposed uses are restricted by the overlay (e.g., uses that attract wildlife or generate smoke/glare) — see § 15.55.050 (AVH) and § 15.54.030 (FP).
• If an overlay standard would render a project infeasible, review the county variance criteria and process (§ 15.54.180 for FP; § 15.55.070 for AVH) and the Variances and Exceptions guidance.

Risks & Ambiguities

Plain‑English Summary

In unincorporated Glenn County overlays are called combining districts. The two overlays you’ll encounter are the FP floodplain overlay (which forces elevation, floodproofing, and special permitting in FEMA‑mapped flood zones — § 15.54.040–070) and the AVH airport hazard overlay (which caps building heights measured to airport reference elevations and restricts hazardous uses near Willows and Orland airports — § 15.55.010–040) — check the county maps and talk to planning before you design.

Source References

• Unified Development Code (Title 15 — Unified Development Code), Title and applicability: § 15.01.010 – § 15.01.030.
• Combining districts list and map authority: § 15.30.020 (shows FP and AVH are combining districts).
• Flood Plain Management Zone (FP): § 15.54.010 – § 15.54.220 (purpose, FEMA map adoption § 15.54.040, development permit § 15.54.070, standards § 15.54.100, floodway § 15.54.160, variances § 15.54.180) .
• Airport Hazard Zone (AVH): § 15.55.010 – § 15.55.080 (purpose § 15.55.010, zones § 15.55.030, height limits § 15.55.040, use restrictions and variances § 15.55.050–070) .

(If you need the county ordinance text excerpts or the official maps in hand, request the planning authority’s copy of the Flood Insurance Study / FIRMs and the airport zoning maps for Willows and Orland; the code requires those be kept on file — § 15.54.040, § 15.55.030.)

Retrieved passages

• Glenn County Zoning Code (§ 2) High relevance show source text
• Glenn County Zoning Code (§ 2) High relevance show source text
• Glenn County Zoning Code (§ 2) High relevance show source text
• Glenn County Zoning Code (§ 2) Medium relevance show source text
• Glenn County Zoning Code (§ 2) Medium relevance show source text
• Glenn County Zoning Code (§ 2) Medium relevance show source text
• Glenn County Zoning Code (Chapter 15.745) Medium relevance show source text
• Glenn County Zoning Code (§ 2) Medium relevance show source text
• Glenn County Zoning Code (§ 3) Medium relevance show source text
• Glenn County Zoning Code (Section 15.54.040) Medium relevance show source text
• Glenn County Zoning Code (chapter and) Medium relevance show source text
• Glenn County Zoning Code (Section 15.54.100.C.2) Medium relevance show source text
• Glenn County Zoning Code (§ 2) Medium relevance show source text
• Glenn County Zoning Code (chapter is) Medium relevance show source text

Cited sections

• Unified Development Code (Title 15 — Unified Development Code), **Title and applicability**: **§ 15.01.010 – § 15.01.030**. (Title 15)
• Combining districts list and map authority: **§ 15.30.020** (shows **FP** and **AVH** are combining districts). (§ 15.30.020)
• Flood Plain Management Zone (FP): **§ 15.54.010 – § 15.54.220** (purpose, FEMA map adoption **§ 15.54.040**, development permit **§ 15.54.070**, standards **§ 15.54.100**, floodway **§ 15.54.160**, variances **§ 15.54.180**) . (§ 15.54.010)
• Airport Hazard Zone (AVH): **§ 15.55.010 – § 15.55.080** (purpose **§ 15.55.010**, zones **§ 15.55.030**, height limits **§ 15.55.040**, use restrictions and variances **§ 15.55.050–070**) . (§ 15.55.010)
• GlennCounty_ZoningCode.md