Local zoning · Windsor

Windsor — Overlay Districts

Q: What level of permit/review applies to changes in a Historic overlay area?

In the -HO overlay, alterations are subject to the Minor Use Permit process (and may be referred to the Commission at the Director’s discretion), demolition is subject to a Conditional Use Permit, and interior renovations or re-roofs that require Building Permits may be handled administratively by the Director. Also comply with Chapter 17.24 for standards. § 17.18.050.E.2–E.3; § 17.18.050.F.

Q: Do I always need CEQA review for work in an overlay?

The -HO overlay notes new development is subject to the permitting process of the underlying zone and “will be subject to environmental review consistent with CEQA” where required; CEQA applicability depends on the nature/scale of the project. § 17.18.050.E.1.

Overlay Districts under the Windsor local zoning and planning code, with the controlling citations.

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Last reviewed: July 3, 2026

Overview

Windsor's overlay districts are geographic modifiers applied as suffixes to base zones to address site-specific safety, environmental, and design issues that the base zone standards alone do not cover. Overlay rules supplement the underlying zone: where they conflict, the overlay controls. The primary overlay districts in the Town's Zoning Code are the -AS (Airport Safety), -FH (Flood Hazard), and -HO (Historic Overlay). The rules and procedures for these overlays are found in Title 17 (the Zoning Code) and applied via the Town's Zoning Map. § 17.06.020 and Chapter 17.18 govern overlay applicability and the three named overlays.

Note: use the Town of Windsor Zoning Map on file with the Planning Division to determine whether a parcel carries an overlay; the Code treats overlay symbols as suffixes to base-zone symbols. § 17.06.020.A.

(First-time internal links: see the Town's Windsor Zoning page for how overlay suffixes appear on the map, and the Windsor Development Standards page for related dimensional requirements.)

How the overlays work (code basics)

Overlays are applied as suffixes to base zones (e.g., MDR-FH, CR-HO) and are mapped on the Zoning Map. § 17.06.020.A.
Overlay provisions are additional to base-zone regulations; if conflict exists, the overlay provision controls. § 17.06.020.C.
The overlay chapter sets special permit, construction, and performance requirements in addition to the underlying zone’s permit and use rules. § 17.18.010–.020.

District-by-district breakdown

Below are focused summaries of each Windsor overlay with purpose, typical permitted uses (how the overlay treats underlying uses), and the most decision-relevant development standards. Each subsection cites the controlling Windsor Zoning Code §.

Table of key items (permitted-use rules and controls) follows this section.

-AS (Airport Safety Overlay)

Purpose: protect people/property from airport-related safety and noise impacts and align Town zoning with the Sonoma County Airport Land Use Commission policies. § 17.18.030.A.
Allowed uses: Any use allowed by the underlying base zone remains allowed, but it must comply with the Airport Land Use Plan (ALUP) and the overlay’s additional constraints. § 17.18.030.C.
Key standards and requirements:
- Height limits: ALUP height constraints apply if more restrictive than base or general regulations. § 17.18.030.E.1.
- Open-space and intensity controls: The ALUP’s open-space definitions and intensity limits apply where more restrictive; the Town may impose limits on employees/business types through recorded agreements prior to permits. § 17.18.030.E.2–E.3.
- Noise insulation: Buildings must be designed/constructed to achieve the CNEL standard in the General Plan Noise Element. § 17.18.030.E.4.
- Avigation easements / noise agreements: Prior to issuance of Building Permits, Tentative Maps, or land-use permits the property owner must execute and record avigation easements/noise agreements with Sonoma County and record them. § 17.18.030.E.5.
Where it applies: lands inside the Sonoma County Airport referral area as designated in the ALUP. § 17.18.030.B.

Practical guidance: verify ALUP numeric height and noise contours directly with the Sonoma County Airport Land Use Commission and confirm any required recorded agreements with Town staff before submitting building or subdivision applications. § 17.18.030.E.

(First-time internal mention: if your project will affect parking, see Windsor’s Windsor Parking page for general parking rules referenced by the Code.)

-FH (Flood Hazard Overlay)

Purpose: minimize flood risk to people/property and prevent increases to flood hazard on neighboring properties. § 17.18.040.A.
Allowed uses: Uses allowed by the underlying base zone are allowed only if they meet the overlay’s floodproofing and elevation standards. § 17.18.040.C.
Key development standards:
- No basements below ground level. § 17.18.040.D.1.
- Lowest floor (lower floor) must be elevated a minimum of 1 ft above the FEMA flood profile level. § 17.18.040.D.1.
- Top of foundations must be 6 inches above the flood profile level; foundations must resist water pressure. § 17.18.040.D.1–D.2.
- The Town may require professional studies (topographic/engineering) to determine flood effects; the Town Engineer may assist in locating flood profile levels for smaller sites. § 17.18.040.D.3.
Where it applies: areas mapped by FEMA and additional areas the Town Engineer identifies as at risk. § 17.18.040.B.

Practical guidance: obtain FEMA elevation/flood profile data early; the Code gives the Town Engineer authority to help locate flood profiles for single-parcel or small development sites and allows the Town to require flood studies. § 17.18.040.D.1–D.3.

-HO (Historic Overlay)

Purpose: protect structures, parcels, and areas with historic or architectural value that contribute to the Town’s heritage. § 17.18.050.A.
Allowed uses: Any use allowed in the underlying base zone is allowed, provided it meets the overlay’s development standards and Chapter 17.24 (Historic Preservation/Conservation). § 17.18.050.C & .F.
Permit and review requirements:
- New development follows the permitting path of the underlying base zone and is subject to CEQA as applicable. § 17.18.050.E.1.
- Alterations to historic resources are subject to the Minor Use Permit process; demolition is subject to the Conditional Use Permit process (Chapter 17.58). The Director may refer Minor Use Permits to the Commission. § 17.18.050.E.2–E.3.
- Interior renovations and roofing that require building permits are subject to administrative review by the Director. § 17.18.050.E.3.
- Development must follow the Historic Conservation and Preservation Standards in Chapter 17.24, and the California Historical Building Code may apply for preservation work. § 17.18.050.F.3–F.6.
Where it applies: areas identified as having special historical, architectural, or aesthetic interest; boundaries are mapped by the Zoning Map. § 17.18.050.B.

Practical guidance: expect a higher-level discretionary review for exterior changes and a likely referral to the Historic standards in Chapter 17.24; early consultation with the Planning Division and the Windsor Design Review process is advisable. Also consult the Town’s Windsor Historic Preservation guidance where available.

Quick-reference table — decision-relevant items

Overlay	Most decision-relevant standard(s) / permitted-use rule	Code reference
-AS (Airport Safety)	ALUP controls height, open space, and intensity; required noise/avigation easement recorded prior to permits; noise insulation to CNEL standard.	§ 17.18.030.E.1–E.5
-FH (Flood Hazard)	No basements; lowest floor elevated 1 ft above FEMA flood profile; foundations 6 in above profile; Town may require flood studies.	§ 17.18.040.D.1–D.3
-HO (Historic Overlay)	Underlying uses allowed if meeting overlay standards; alterations = Minor Use Permit, demolition = Conditional Use Permit; complies with Chapter 17.24 and California Historical Building Code.	§ 17.18.050.C, .E.2–E.3, .F
Mapping & precedence	Overlays appear as suffixes on the Zoning Map and overlay provisions control where they conflict with base zone.	§ 17.06.020.A & .C

Checklist

Confirm whether the parcel carries -AS, -FH, or -HO on the Town’s Zoning Map. § 17.06.020.A.
Review the underlying base zone standards and applicable special permits; overlay requirements are additive and control in conflict. § 17.06.020.C; § 17.18.010–.020.
For -AS: check ALUP height/noise contours; prepare to execute/record avigation/noise easement agreements as required before Building Permit/Tentative Map/land-use permit issuance. § 17.18.030.E.1–E.5.
For -FH: obtain FEMA flood profile elevations, design floor elevation 1 ft above flood profile, ensure foundations top at 6 in above profile, and be ready to provide engineering/topographic studies if requested by the Town Engineer. § 17.18.040.D.1–D.3.
For -HO: determine whether proposed work is an alteration (Minor Use Permit), demolition (Conditional Use Permit), or routine interior work (administrative review); apply Chapter 17.24 historic standards and CEQA where applicable. § 17.18.050.E–F; Chapter 17.24.
Confirm whether design review processes are triggered and consult the Town’s design-review guidance prior to final application. § 17.18.050.E; see Chapter 17.24. (See Windsor Design Review.)
Coordinate early with the Town Engineer and Planning Division for flood and ALUP technical determinations. § 17.18.040.D.3; § 17.18.030.E.1–E.3.

Risks & Ambiguities

Issue	Why it matters	What to verify
Overlay boundaries for a parcel	Permits, allowed uses, and standards change if an overlay applies.	Confirm parcel overlay status on the official Zoning Map with the Planning Division. § 17.06.020.A.
Numeric ALUP limits (heights, buffers)	The Code defers to the ALUP for numeric limits; the Code text does not reproduce those numbers.	Obtain the Sonoma County ALUP for numeric height, safety zones, and required open-space measures; confirm which ALUP provisions are more restrictive. § 17.18.030.E.1–E.3.
Exact flood profile elevation for a parcel	The overlay requires elevations relative to FEMA profile; small-parcel elevations may not be obvious from maps.	Request Town Engineer assistance to locate the flood profile for small sites; verify if a flood study is required. § 17.18.040.D.1–D.3.
Whether a work item is "alteration" vs. routine repair in -HO	Different permit paths and hearings apply (Minor Use Permit vs. administrative review).	Confirm classification with Planning staff and review Chapter 17.24 and 17.58 processes. § 17.18.050.E.2–E.3.
Interaction with state codes (e.g., historical buildings)	Preservation work may trigger California Historical Building Code or other state standards.	For preservation standards and applicability of the California Historical Building Code, verify with Building Official; see Code references to historic standards. § 17.18.050.F.6.

Information Gaps (what the retrieved materials did not show)

The Zoning Code references ALUP numeric height limits and Airport referral areas, but the ALUP's numerical height and precise contour data are not printed in the retrieved Code. Not found in retrieved materials — verify with Sonoma County ALUP and Town staff. § 17.18.030.E.1–E.3.
The Code indicates overlay boundaries are on the Zoning Map, but the retrieved text does not include parcel-level maps or an online overlay-layered map. Not found in retrieved materials — confirm with the Planning Division. § 17.06.020.A.
Specific treatment of Accessory Dwelling Units (ADUs) inside overlays is not described in the overlay sections retrieved. Not found in retrieved materials — check the Town ADU rules and California ADU law for overlay interaction. (See Windsor ADUs and California ADU law.)

Plain-English Summary

If your Windsor property has a suffix like -AS, -FH, or -HO on the Zoning Map, the overlay adds rules you must follow on top of your base zone: airport areas require height/noise protections and recorded avigation easements, flood areas require no basements and raised floors (1 ft above flood profile, 6 in top of foundation), and historic areas require extra review for exterior changes (minor or conditional permits) and adherence to the Town’s historic standards. Confirm map status, talk to Planning and the Town Engineer early, and expect recorded agreements or technical studies for AS and FH overlays. § 17.06.020; §§ 17.18.030, 17.18.040, 17.18.050.

Source References

§ 17.06.020 Establishment of Zones; Overlay Zones (mapping, applicability, and precedence).
§ 17.18.010 Purpose of Chapter — Overlay Zones.
§ 17.18.020 Applicability of Overlay Zones (mapping as suffixes, conflicts).
§ 17.18.030 Airport Safety Overlay Zone (-AS) (purpose, applicability, development standards including height, open space, noise, avigation easements).
§ 17.18.040 Flood Hazard Overlay Zone (-FH) (purpose, applicability, no basements, elevation/foundation requirements, required studies).
§ 17.18.050 Historic Overlay Zone (-HO) (purpose, applicability, permit processes, referral to Chapter 17.24).
Chapter 17.24 (Historic Preservation and Conservation) — referenced as required guidance for -HO compliance. Not reproduced here; consult Town files.

(Also consult the Town’s official Zoning Map on file with the Planning Division to confirm parcel overlays; the Code incorporates that map by reference. § 17.06.010–.020. )

Sources

Retrieved passages

CBC § 050 (Chapter 17.58) High relevance
Windsor Zoning Code (Chapter 17.18.) Medium relevance
Windsor Zoning Code Medium relevance
Windsor Zoning Code Medium relevance
Windsor Zoning Code (section shall) Medium relevance
Windsor Zoning Code (§ 2) Medium relevance
Windsor Zoning Code (article for) Medium relevance
Windsor Zoning Code (§1-6-11) Medium relevance

Cited sections

Official Windsor code library

Frequently asked questions

What overlays might appear on my Windsor parcel and how do I tell?

Overlays in Windsor appear as suffixes on the official Zoning Map (for example, MDR-FH or CR-HO) — the Town’s Zoning Map on file with the Planning Division shows whether your parcel has -AS, -FH, or -HO. Overlay symbols are applied as suffixes to base-zone symbols and the overlay rules supplement the base zone rules. § 17.06.020.A & § 17.18.020.

What uses are allowed in an overlay (can I still build the same uses as my base zone)?

Yes — the overlays state that any use normally allowed in the underlying base zone may be allowed, but that use must also comply with the overlay’s additional requirements (e.g., ALUP limits in -AS, elevation/floodproofing in -FH, historic standards and permits in -HO). § 17.18.030.C; § 17.18.040.C; § 17.18.050.C.

If my parcel is in the Flood Hazard overlay, how high must I build?

The Code requires the lower floor to be elevated a minimum of 1 ft above the FEMA flood profile level and foundation tops 6 inches above that flood profile; basements below ground are prohibited. The Town Engineer can assist in locating the flood profile for small sites and the Town may require engineering studies. § 17.18.040.D.1–D.3.

If my parcel is in the Airport Safety overlay, can I be required to record an avigation easement?

Yes. Prior to issuance of a Building Permit, Tentative Map, or approval of a land use permit, the property owner may be required to execute and record avigation easements or noise agreements with Sonoma County, and the Town will require them be recorded. § 17.18.030.E.5.

What level of permit/review applies to changes in a Historic overlay area?

In the -HO overlay, alterations are subject to the Minor Use Permit process (and may be referred to the Commission at the Director’s discretion), demolition is subject to a Conditional Use Permit, and interior renovations or re-roofs that require Building Permits may be handled administratively by the Director. Also comply with Chapter 17.24 for standards. § 17.18.050.E.2–E.3; § 17.18.050.F.

Does the overlay ever override the base zone on things like setbacks or height?

Yes — overlay provisions are intended to be additional and the Code specifies that where there is a conflict between overlay regulations and other Zoning Code provisions, the more restrictive (i.e., the overlay where it is intended to govern) shall apply. § 17.06.020.C; § 17.18.020.B.

Where do I find the numeric height limits that apply in the Airport Safety overlay?

The Windsor Zoning Code defers to the Sonoma County Airport Land Use Plan (ALUP) for numeric height limits and safety zones; the Code does not reproduce ALUP numeric tables. Obtain the ALUP for numeric limits and verify which ALUP provisions are more restrictive for your parcel. § 17.18.030.E.1–E.3.

Will adding an ADU be restricted by an overlay?

The overlay chapters state that underlying uses are allowed if they comply with overlay standards, but the overlay chapters retrieved do not specifically address Accessory Dwelling Units (ADUs). You should consult Windsor’s ADU rules and the Town for parcel-specific overlay interaction; the Code does not explicitly state ADU procedures within overlays in the retrieved materials. Not found in retrieved materials — verify with the Planning Division.

Do I always need CEQA review for work in an overlay?

The -HO overlay notes new development is subject to the permitting process of the underlying zone and “will be subject to environmental review consistent with CEQA” where required; CEQA applicability depends on the nature/scale of the project. § 17.18.050.E.1.

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