Local zoning · Sonoma County

Sonoma County — Historic Preservation

Historic Preservation under the Sonoma County local zoning and planning code, with the controlling citations.

Last reviewed: July 6, 2026

Overview

This page explains how historic preservation works under Sonoma County’s zoning ordinance for unincorporated areas. The County uses combining “overlay” districts to recognize historic resources and require special design oversight without changing base zoning uses. The core tool is the HD Historic Combining District, administered with the County Landmarks Commission; some overlay districts with local design guidelines also trigger historic review. The zoning ordinance is Chapter 26 of the Sonoma County Code; all citations below use Chapter 26 sections.

Key rule: Exterior work (including demolition) on a designated historic structure, or any new building in a mapped historic district, requires County Landmarks Commission approval before a zoning permit can be issued. See § 26-68-020.

What the Sonoma County Zoning Ordinance Covers

The HD Historic Combining District purpose, designation, review triggers, decision standards and appeals. §§ 26-68-005, 26-68-010, 26-68-020, 26-68-025, 26-68-030, 26-68-040.
Where combining districts, including HD, are established and mapped in the official zoning database. §§ 26-02-100, 26-02-130.
Local guideline overlays (LG) that require concurrent Landmarks Commission review when historic resources are present (e.g., Penngrove Main Street; Russian River Corridor). §§ 26-90-080(b)(3), 26-90-090(b)(3).
Special nonconforming rules for authenticated historic structures. § 26-94-040(b).

The ordinance makes clear the Landmarks Commission’s scope is limited to design; it does not change underlying uses or other entitlements. § 26-68-020. For parallel processes like design review, development standards, signage, and parking, the base zoning still applies unless a mapped guideline or condition says otherwise.

District-by-District Guide (Historic-Related Overlays)

HD Historic Combining District

Purpose: Protect structures, sites, and areas important for local/state/national history or architecture; preserve unique, irreplaceable assets. § 26-68-005.
Where it applies: Wherever the HD overlay is mapped in the County’s official zoning database (unincorporated areas only). §§ 26-02-100, 26-02-130.
Typical permitted uses: Same as the underlying base district; HD adds a design-review layer only. § 26-68-020.
Key dimensional standards: Base-zone height, setbacks, coverage, etc., continue to apply unless additional standards are stated on the historic district’s sectional map. § 26-68-030(b).
Review triggers:
- Exterior alterations (including demolition) of a designated historic structure. § 26-68-020.
- New construction within a designated historic district. § 26-68-020.
- Minor alterations may be approved by staff consistent with adopted historic design guidelines. § 26-68-020.
Decision standards: Commission applies the article’s purpose and any standards delineated on the district’s map. § 26-68-030.
Appeals: Any interested person may appeal Commission decisions to the Planning Commission and then to the Board of Supervisors. § 26-68-040.

HD — Bodega Historic District

Purpose: Same as HD overlay; conformance with adopted Bodega Historic District Design Guidelines. §§ 26-68-005, 26-68-025.
Where it applies: Mapped HD overlay area in Bodega (unincorporated). § 26-02-130.
Typical permitted uses: Underlying zoning uses still control; HD adds design review. § 26-68-020.
Key dimensional standards: Base-zone standards unless map-specific standards exist; verify with guidelines. § 26-68-030(b).

HD — Freestone Historic District

Purpose: Same as HD overlay; conformance with adopted Freestone Historic District Design Guidelines. §§ 26-68-005, 26-68-025.
Where it applies: Mapped HD overlay area in Freestone (unincorporated). § 26-02-130.
Uses and dimensional standards: Same approach as Bodega HD district. §§ 26-68-020, 26-68-030(b).

HD — Occidental Historic District

Purpose: Same as HD overlay; conformance with adopted Occidental Historic District Design Guidelines. §§ 26-68-005, 26-68-025.
Where it applies: Mapped HD overlay area in Occidental (unincorporated). § 26-02-130.
Uses and dimensional standards: Same approach as Bodega HD district. §§ 26-68-020, 26-68-030(b).

LG/PNG Penngrove Main Street (Historic-Related)

Purpose: Preserve Penngrove Main Street’s historic resources and traditional character through local design guidelines. § 26-90-080(a).
Where it applies: Properties mapped LG/PNG in Penngrove (unincorporated). § 26-90-080(d).
Uses and dimensional standards: Follow underlying zoning; LG invokes design review. § 26-90-040(a).
Historic trigger: If a site is on the County Historic Resources Inventory or within HD, Landmarks Commission (or staff) must review concurrently with design review. § 26-90-080(b)(3).

LG/RRC Russian River Corridor (Historic-Related)

Purpose: Preserve and enhance the area’s built environment; ensure compatible new development. § 26-90-090(a).
Where it applies: Properties mapped LG/RRC in the Russian River Corridor (unincorporated). § 26-90-090(d).
Uses and dimensional standards: Follow underlying zoning; LG invokes design review. § 26-90-040(a).
Historic trigger: If a site is listed in Appendix B (Historic Resources), the County Historic Resources Inventory, or in HD, Landmarks Commission (or staff) review is required concurrently with design review. § 26-90-090(b)(3).

Decision-Relevant Standards and Triggers

What you want to do	Do you need Landmarks Commission sign-off?	Notes	Code Reference
Alter exterior of a designated historic structure	Yes	Includes demolition; staff may approve “minor” alterations per adopted guidelines	§ 26-68-020
Build a new structure within a mapped historic district (HD)	Yes	Commission approval required before zoning permit	§ 26-68-020
Demolish a structure in a historic district	Yes	Commission must act within 6 months of application	§ 26-68-020
Follow adopted district guidelines (Bodega, Freestone, Occidental)	Yes	Mandatory conformance	§ 26-68-025
Rely on base zone uses and dimensional standards	Generally yes	HD does not add use controls; additional map-specific standards may apply	§§ 26-68-020, 26-68-030(b)
Historic resource in LG/PNG or LG/RRC	Yes, concurrent with design review	Landmarks Commission/staff review runs with design review	§§ 26-90-080(b)(3), 26-90-090(b)(3)
Appeal a Landmarks Commission decision	Available	Appeal to Planning Commission; further appeal to Board of Supervisors	§ 26-68-040
Repair a legal nonconforming historic structure beyond usual 20% cap	Potentially allowed	If in HD or listed and certified historic; must be an authentic replica	§ 26-94-040(b)

Process and Roles

Mapping: The County formally maps the HD overlay through standard zoning amendment procedures; boundaries are in the official zoning database. §§ 26-68-010, 26-02-130.
Review authority: The Landmarks Commission is the decision-maker for HD-related design approvals; it applies article purposes and any map-specific standards. § 26-68-030.
Scope: The Commission’s jurisdiction is design review only; it does not decide uses or other zoning entitlements. § 26-68-020.
Local Guidelines areas: Projects in certain LG overlays must undergo design review and, where historic resources are present, concurrent Landmarks Commission or staff review. §§ 26-90-040(a), 26-90-080(b)(3), 26-90-090(b)(3).

Practical Notes

The HD overlay is an “extra layer” on your base zoning, not a replacement; expect added design scrutiny, not different allowed uses. § 26-68-020.
Expect your submittal to address conformance with any adopted historic district guidelines (Bodega, Freestone, Occidental) and any map-specific standards. § 26-68-025; § 26-68-030(b).
If your building is legal but nonconforming, and it’s historic, you may have more flexibility for repairs than typical nonconforming structures. Check § 26-94-040(b) and coordinate with Nonconforming Uses.
For site planning matters like landscaping and screening, signage, and parking, use the base-zone standards unless a historic guideline or approval sets objective alternatives.

Checklist

Confirm if your parcel is mapped with the HD overlay in the official zoning database (unincorporated areas only). § 26-02-130.
Determine if your site is listed on the County Historic Resources Inventory or within LG areas that invoke historic review (Penngrove Main Street; Russian River Corridor). §§ 26-90-080(b)(3), 26-90-090(b)(3).
If in HD or otherwise historic, prepare a design package addressing applicable historic district guidelines (Bodega, Freestone, Occidental). § 26-68-025.
File for the appropriate design review permit; coordinate for concurrent Landmarks Commission review where required. §§ 26-68-020, 26-90-040(a).
If demolition is proposed in HD, plan for Commission action within six months of a complete application and build that into your schedule. § 26-68-020.
If the structure is legal nonconforming and historic, document qualifications for the § 26-94-040(b) repair/reconstruction flexibility.
If an approval is denied, consider appeal timelines and grounds to the Planning Commission, then Board. § 26-68-040.

Risks & Ambiguities

Issue	Why it matters	What to verify
“Minor alterations” not defined	Staff may approve “minor” changes; unclear threshold can affect timeline/route	Ask staff whether your scope qualifies as minor per the adopted guideline for your district. § 26-68-020.
Map-specific standards	Extra standards may be embedded on the sectional district map	Confirm if any numeric limits or features are mapped for your HD area. § 26-68-030(b).
LG overlay triggers	Some LG areas force concurrent historic review	Check LG/PNG and LG/RRC boundaries and Inventory status before assuming a ministerial path. §§ 26-90-080(b)(3), 26-90-090(b)(3).
Nonconforming “historic” qualification	Extra repair flexibility depends on formal certification and authenticity	Verify if your structure meets all § 26-94-040(b) criteria and what evidence is required.
Signage in HD	Signs often shape historic character	Whether special sign criteria apply in your district is Not found in retrieved materials; consult Signage and any local guideline.
Base-zone vs. HD conflicts	Dimensional/architectural asks may clash with base-zone standards	Early design review consult and, if needed, variances. Verify with the jurisdiction.

Plain-English Summary

If your property in unincorporated Sonoma County is designated historic or sits inside a mapped historic district, you’ll keep your normal zoning uses, but any exterior work (or new construction) must pass a Landmarks Commission design check for historic compatibility. Some local guideline overlays also trigger a concurrent historic review. Plan early for HD guidelines and Commission timelines, and coordinate with design review so you don’t redo plans later. §§ 26-68-020, 26-68-025, 26-90-040, 26-90-080(b)(3), 26-90-090(b)(3).

Information Gaps

Numeric design standards within the Bodega, Freestone, and Occidental guidelines: Not found in retrieved materials. Verify with the jurisdiction.
Any Countywide, HD-specific sign standards or objective architectural metrics beyond district guidelines: Not found in retrieved materials.
The detailed procedures/criteria for initiating HD designation (beyond “normal zoning procedures”): Not found in retrieved materials.

Source References

§ 26-02-020 (Zoning ordinance purpose; lists Article 68 as open space zoning).
§ 26-02-100 (Combining districts enumerated; includes HD).
§ 26-02-130 (Official zoning database).
§§ 26-68-005, 26-68-010, 26-68-020, 26-68-025, 26-68-030, 26-68-040 (HD Historic Combining District purpose, designation, review triggers, guidelines, standards, appeals).
§§ 26-90-040, 26-90-080(b)(3), 26-90-090(b)(3) (Local Guideline overlays; concurrent historic review triggers).
§ 26-94-040(b) (Nonconforming historic structures—repair flexibility).

Sources

Retrieved passages

Sonoma County Zoning Code (Article 68.) High relevance
Sonoma County Zoning Code (chapter to) High relevance
Sonoma County Zoning Code (Chapter 26) High relevance
Sonoma County Zoning Code (Chapter 26) High relevance
Sonoma County Zoning Code Medium relevance
Sonoma County Zoning Code (Section 26-24-280) Medium relevance
Sonoma County Zoning Code (Section 26-88-015) Medium relevance
Sonoma County Zoning Code (section including) Medium relevance

Cited sections

Official Sonoma County code library

Frequently asked questions

What is the HD Historic Combining District in unincorporated Sonoma County?

It’s an overlay that protects historic structures and districts by requiring design-focused review of exterior work and new construction; it does not change base zoning uses. See §§ 26-68-005 and 26-68-020.

Do I need Landmarks Commission approval to replace windows or siding on a historic property?

Yes, if the structure is designated or lies within an HD district. Exterior alterations require approval; “minor” changes may be approved by staff under adopted guidelines. § 26-68-020.

How long can the County take to act on a demolition request in a historic district?

For demolition-only requests within an HD district, the Landmarks Commission must act within six months of the application date. § 26-68-020.

Where are County-designated historic districts with adopted guidelines?

Bodega, Freestone, and Occidental have adopted historic district design guidelines; projects must conform to them. § 26-68-025.

Does the HD overlay change what I’m allowed to use my property for?

No. The Landmarks Commission’s jurisdiction is limited to design; base-zone uses and entitlements remain in place. § 26-68-020.

How do I appeal a Landmarks Commission decision?

Any interested person may appeal to the Planning Commission, then to the Board of Supervisors, following the ordinance’s appeal procedures. § 26-68-040.

I’m in Penngrove Main Street/Russian River Corridor—does historic review still apply?

If your site is a listed historic resource or in HD, the Landmarks Commission (or staff) must review your project concurrently with design review. §§ 26-90-080(b)(3), 26-90-090(b)(3).

Can I repair a nonconforming historic building beyond the standard 20% repair cap?

Possibly. If the structure meets the ordinance’s historic criteria and the work is an authentic replica, the 20% cap can be waived for nonconforming commercial/industrial buildings. § 26-94-040(b).

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