Humboldt County — Overlay Districts

Last reviewed: July 3, 2026

Overview

Overlay districts in Humboldt County (officially called Combining Zones) are additional zoning designations placed on top of a property's primary zone to modify permitted uses, development standards, or procedure in the county’s unincorporated areas. The Combining Zone rules operate alongside the principal zone rules and — where specified — supersede them; the combining-zone program and the list of named overlays are codified in the Humboldt County Zoning Regulations (Combining Zone chapter) and the coastal/inland tables of combining-zone sections. See § 15.1–15.3 for purpose and applicability and the combining-zone tables for coastal/inland designators.

Note: this page covers only overlay/combining-zone rules that apply in the unincorporated areas of Humboldt County; incorporated cities inside the county have separate codes.

How the code treats overlays (quick legal points)

• A Combining Zone modifies the regulation of the principal zone where applied; otherwise the principal zone controls. § 15.1–§ 15.2.
• The code publishes separate combining-zone tables for Coastal (e.g., § 313‑16.3, § 313‑21.1) and Inland (e.g., § 314‑16.1, § 314‑21) areas — use the table appropriate to the map designation.
• Where multiple overlays apply, the most restrictive regulation controls unless a specific overlay (e.g., STMP) states a different conflict rule; the STMP combining zone is explicitly given precedence over other regulations where it applies. § 34.5.3.

For practical guidance on development standards you may need, consult Humboldt County’s development standards page (setbacks, lot coverage, and similar) and the county’s parking, design review, and development standards guidance while preparing applications.

District-by-district breakdown (selected, high‑value overlays)

Note: the code lists many combining zones. Below are the most commonly encountered overlays in unincorporated Humboldt County and what the zoning ordinance text establishes for each. Where the ordinance text in the retrieved files contains district-level standards, those items are shown and cited. Where the ordinance text in the retrieved materials does not state a required numeric standard or use list, the entry says "Not found in retrieved materials" and you should Verify with the jurisdiction.

AP — Airport Safety Review (coastal § 313‑16.3; inland § 314‑16.1)

• Purpose: Maintain compatibility of land uses with airports (safety, height, density). § 313‑16.3 / § 314‑16.1.
• Typical permitted uses: Varies by subarea (clear, approach, transitional, beneath flight track); many residential or high‑occupancy uses require a Special Permit (SP) in approach/clear zones. See the AP matrix for exact use-permit triggers. § 16.3.3 / AP matrix.
• Key dimensional/operational standards: No structure, tree, or object allowed to exceed FAA-derived height limits (see local code reference to Section 331). Buildings over 35 ft may be allowed only with a Special Permit. Maximum density in an approach zone is 1 unit per 3 acres unless a Special Permit or Director approval provides an exception. § 16.3.4.1–16.3.4.3.
• Where it applies: Parcels mapped with the AP designator on the zoning maps; also to lands listed in the Humboldt County Airports Master Plan technical report. § 16.3.2.

F — Flood Hazard Areas (coastal § 313‑21.1; inland § 314‑21)

• Purpose: Reduce flood risk to life/property and protect floodplain functions. § 313‑21.1 / § 314‑21.
• Typical permitted uses: Varies; certain structures or uses may be prohibited or require flood‑risk mitigation and floodplain permitting. Specific allowed/conditional uses are set in the overlay-specific subsections (see code). Not all numeric standards are printed in the retrieved snippets. Verify with the county for the full flood-plain use table. Not found in retrieved materials for detailed construction limits.
• Key standards shown in the code: Flood overlays add required development standards in addition to the principal zone (see flood combining zone section for elevation, foundation, or setback requirements where present). Verify with county for V zones, AE zones, and local flood elevation references. Not found in retrieved materials for specific base flood elevations in the code excerpt.
• Where it applies: Parcels mapped with the F designator or areas otherwise identified on the zoning map. § 313‑21.1 / § 314‑21.

G — Alquist‑Priolo Fault Hazard (coastal § 313‑22.1; inland § 314‑22.1)

• Purpose: Prevent construction of structures for human occupancy across known active faults; ensure geologic setback and investigation. § 313‑22.1 / § 314‑22.1.
• Typical permitted uses: Many uses allowed but require site investigation, setbacks, or special permits before development. Specific triggers and mitigation measures are in the overlay subsection. Not found in retrieved materials for exact required investigation reports or setback distances — Verify with the jurisdiction.
• Where it applies: Properties mapped with the G designator. § 313‑22.1 / § 314‑22.1.

D — Design Review (coastal § 313‑19.1; inland § 314‑19)

• Purpose: Control exterior design, materials, and site layout to protect scenic and neighborhood character. § 313‑19.1 / § 314‑19.
• Typical permitted uses: The overlay does not change allowed uses but requires discretionary design review approval for certain projects (new construction, additions, nonresidential façades). See the Design Review combining-zone subsection for permit triggers. Not all triggers are present in the retrieved excerpt; Verify with county.
• Where it applies: Parcels shown with D on zoning maps. If your project triggers design review, consult the county’s design review guidance.

STMP — Samoa Town Master Plan (coastal § 313‑34.5, also shown as 34.5)

• Purpose: Provide comprehensive, area‑specific development rules for the Samoa community (STMP Land Use Plan). § 34.5.1 / § 313‑34.5.
• Typical permitted uses: The STMP combining zone contains its own land‑use map and reserved permitted uses; the principal permitted use in STMP is determined by the land use designations shown on the certified STMP Land Use Map. § 34.5.3.
• Key standards: STMP regulations are “in addition to” principal zone rules and where conflicts arise the STMP regulations take precedence (i.e., STMP is controlling within its mapped area). Recordation/parcel map conditions and certain subdivision prerequisites are specified for the STMP overlay. § 34.5.2–34.5.4.
• Where it applies: A discrete set of APNs described in the STMP/LUP and shown on Exhibit 25; consult the STMP map in the zoning code for exact boundaries. § 34.5.2.

R — Streams and Riparian Corridor Protection (coastal § 313‑33.1; inland § 314‑38.1 / WR)

• Purpose: Protect stream corridors and riparian habitat through setbacks and restricted disturbance. § 313‑33.1.
• Typical permitted uses: Limited disturbance; often allowed accessory uses with mitigation. Specific allowed uses, setback widths, and mitigation obligations are specified in the combining-zone subsection — not all numeric setbacks are shown in the retrieved snippets. Verify with the county for setback distances and buffer treatments.

Quick reference table — key overlays and code anchors

Checklist — what an application must address when an overlay applies

• Identify all combining zones mapped over the parcel on the county zoning map; cite each overlay designation (e.g., AP, F, D). Verify against the county zoning map and staff. § 15.2.
• For each overlay, include the overlay‑specific required studies (e.g., geologic report for G, flood study for F, airport/height analysis for AP) as described in the combining‑zone subsection. Verify exact submittal requirements with staff. Not all required submittals are in the retrieved materials — Verify with the jurisdiction.
• If the overlay imposes discretionary review (Design Review, Special Permits), prepare the corresponding design packet and responses to applicable findings (see § 16.3.4 and the Design Review subsection).
• Confirm whether the overlay changes numeric development standards (setbacks, lot-size, density) or simply adds procedural requirements; where STMP applies, expect STMP rules to control. § 34.5.3.
• Cross-check overlay requirements with the county’s development standards and parking rules; provide plans that address both overlay and principal‑zone rules.

Risks & Ambiguities

Plain‑English summary

If your parcel in an unincorporated part of Humboldt County has one or more overlay (Combining Zone) flags on the zoning map — like AP (Airport), F (Flood), G (Fault), D (Design Review), or STMP (Samoa Town Master Plan) — those overlays add extra rules or special permits on top of the normal zoning rules; some set required studies (geologic, flood), some limit building height or density (AP), and some (like STMP) can override the regular zone rules within their mapped boundary. Always check the combining‑zone subsection that corresponds to each overlay shown on your parcel and verify the parcel mapping with county staff.

Source References

• Combining zone purpose and applicability: § 15.1–15.3 (Combining Zones general rules).
• Coastal combining-zone table (maps combining-zone codes to code subsections, e.g., § 313‑16.3 AP, § 313‑21.1 F, § 313‑34.5 STMP).
• Inland combining-zone table (e.g., § 314‑16.1 AP, § 314‑21 F).
• Airport Safety Review details and AP matrix / development standards: § 16.3.1–16.3.4 (includes height, density, special‑permit rules).
• Samoa Town Master Plan combining‑zone text and applicability: § 34.5.1–34.5.4 (STMP precedence and parcel list / Exhibit 25).
• For code‑level zone tables and principal zone designations (RS, RM, MC, TPZ, etc.): § 313‑2.1–313‑7.3 (table of principal zones referenced in the combining-zone chapter).

Also consult these county web pages for practical application guidance while preparing a submittal: Humboldt County zoning & planning overview, Humboldt County Zoning, Humboldt County Land Use, Humboldt County Development Standards, Humboldt County Parking, Humboldt County Design Review, Humboldt County Historic Preservation, Humboldt County Signage, Humboldt County Variances and Exceptions, Humboldt County Landscaping and Screening, California Building Standards Code, and California ADU law.

Retrieved passages

• Humboldt County Zoning Code (§ 1) Medium relevance show source text
• Humboldt County Zoning Code (§ 1) Medium relevance show source text
• Humboldt County Zoning Code Medium relevance show source text
• Humboldt County Zoning Code Medium relevance show source text
• Humboldt County Zoning Code (Section CZ) Medium relevance show source text
• Humboldt County Zoning Code (section is) Medium relevance show source text
• Humboldt County Zoning Code Medium relevance show source text

Cited sections

• Combining zone purpose and applicability: **§ 15.1–15.3** (Combining Zones general rules). (§ 15.1)
• Coastal combining-zone table (maps combining-zone codes to code subsections, e.g., **§ 313‑16.3 AP**, **§ 313‑21.1 F**, **§ 313‑34.5 STMP**). (§ 313)
• Inland combining-zone table (e.g., **§ 314‑16.1 AP**, **§ 314‑21 F**). (§ 314)
• Airport Safety Review details and AP matrix / development standards: **§ 16.3.1–16.3.4** (includes height, density, special‑permit rules). (§ 16.3.1)
• Samoa Town Master Plan combining‑zone text and applicability: **§ 34.5.1–34.5.4** (STMP precedence and parcel list / Exhibit 25). (§ 34.5.1)
• For code‑level zone tables and principal zone designations (RS, RM, MC, TPZ, etc.): **§ 313‑2.1–313‑7.3** (table of principal zones referenced in the combining-zone chapter). (§ 313)
• HumboldtCounty_ZoningCode.md