Local zoning · Solano County

Solano County — Historic Preservation

Q: What rules govern setbacks, height and lot coverage for older houses when I propose changes?

Apply the district’s development standards (e.g., Table 28‑32C for R‑TC; Table 28‑31C for R‑R). These tables specify minimum lot area, setbacks, and height limits; architectural approval under § 28.102 can also condition design elements. Check the specific table for your zoning suffix (R‑TC‑4, R‑TC‑6, R‑R‑5, etc.).

Q: Where can I get the objective design guidelines the county uses for architectural approval?

The code requires architectural approval under § 28.102 but the specific objective standards are included in district development standards, tables (e.g., Table 28‑32C, Table 28‑31C), and any overlay or policy plan text. Request the applicable district tables and any overlay ordinance from the Planning Division; the code references architectural standards repeatedly in the district chapters.

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

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Last reviewed: July 3, 2026

Overview

Solano County’s zoning regulations do not create a separate county-owned historic-preservation overlay or a single “historic landmarks” chapter for unincorporated areas; instead historic protection is implemented through general tools that affect many districts: architectural approval, development standards in residential districts, special permit findings (zoning clearance / use permits), and limitations tied to state historic rules such as the California Historical Building Code. Key implementing provisions appear in the Residential regulations (Article 28.32 / 28.31), the Architectural Approval rules, accessory-dwelling rules, the Marsh Preservation rules where applicable, and by reference to the State Historical Building Code. See § 28.102, § 28.72.10, § 28.31–28.32, and the CHBC provisions (e.g., 8‑1002.1).

Note: this page treats only rules inside the Solano County Zoning Ordinance for unincorporated areas; building code (Title 24) or tenant/housing-law topics are handled elsewhere. Also see the county pages for related processes for parking, design review, overlays, ADUs, development standards, and nonconforming rules linked below.

For local rules on parking, see the county parking rules. Solano County Parking
For design review and architectural approval procedures, see Solano County Design Review.
For overlay possibilities (including -PP policy plan overlays), see Solano County Overlay Districts.
For ADU rules and special historic protections referenced below, see California ADU law.
For how the county organizes development standards and setbacks, see Solano County Development Standards.
For references to how historic structures interact with the state code, see California Building Standards Code.
For impacts that depend on existing nonconforming status, see Solano County Nonconforming Uses.

How Historic Preservation is Implemented in the Solano County Ordinance (high-level)

Architectural Approval (Design Review): The county requires architectural approval for many new structures and for alterations where exterior design matters; architectural approval is administered under § 28.102 and referenced across multiple district sections (R‑districts, commercial, industrial, marsh areas). That review is the primary local tool the county uses to require compatibility and to prevent “unsightly” changes that would damage historic character.
Accessory Dwelling Units (ADUs) + Historic Resources: The ADU rules explicitly limit ADUs on properties listed on the California Register of Historic Resources: an ADU or junior ADU is not allowed on a parcel listed on the California Register unless the Zoning Administrator makes a written determination that the ADU “would not have a significant adverse impact on the historic resource.” That language is embedded in the Residential/ADU provisions of § 28.72.10.
District development standards with architectural review hooks: Residential districts (particularly R‑TC and R‑R types) include dimensional standards for building height, setbacks, lot area and explicit calls to architectural approval and parking rules; those standards combine with architectural approval to regulate changes affecting historic buildings. See § 28.32.30 (R‑TC tables) and development tables for R‑R districts (Table 28‑31C and § 28.31 series).
Marsh/Resource Areas (MP): Where historic resources fall within Suisun Marsh or other resource zones, the Marsh Preservation District rules (e.g., § 28.52) add permit layers (marsh development permits) and also reference architectural approval and site standards; that can trigger extra review for historic sites in those areas.
State Historical Building Code (CHBC): For qualified historic structures, the State Historical Building Code (CHBC) applies and provides alternative code solutions which the county enforces (refer to CHBC provisions such as 8‑1002.1 and related CHBC chapters). The CHBC explicitly covers qualified historic districts, site features, and allows alternative approaches to preserve historic integrity while addressing life-safety issues.
No single county “historic overlay” located in retrieved materials: The Solano County Zoning Ordinance provides overlays (policy plan overlays, etc.) that can include historic-compatibility standards, but I did not find a dedicated county historic preservation overlay or county landmark register in the materials you provided. "Historic resource" protections are implemented by the district standards, architectural approval, ADU limitations, and by using state CHBC rules where applicable. Not found in retrieved materials.

District-by-District (how historic issues are applied in practice)

Note: all district summaries below apply only to UNINCORPORATED AREAS of Solano County.

R-R (Rural Residential districts; see § 28.31 et seq.)

Purpose: low‑density rural residential.
Typical permitted uses: single‑family dwellings, accessory buildings, secondary dwellings (with permit), and agricultural accessory uses per Table 28‑31A/C. See the allowed‑uses tables tied to § 28.31 and Table 28‑31C.
Key dimensional standards (decision‑relevant): front/side/rear setbacks and accessory-building separations are specified in Table 28‑31C (setbacks; height 35 ft typical; between structures minimums). See § 28.31 tables for lot‑area/setback metrics.
Historic-preservation effect: changes to an older home in an R‑R district that affect exterior appearance or add new structures will typically need architectural approval and a building permit (see § 28.102), and ADUs on historic‑listed parcels are limited unless a written Zoning Administrator finding is made.

R‑TC (Residential — Traditional Community; see § 28.32 and Table 28‑32C)

Purpose: stabilize and preserve higher‑density historic traditional communities outside municipalities.
Typical permitted uses: single‑family dwellings, multi‑family in specific subdistricts, accessory dwellings (subject to the standards in § 28.72.10 and Table 28‑32C).
Key dimensional standards (decision‑relevant): minimum lot areas by suffix (R‑TC‑4 = 4,000 sf, R‑TC‑6 = 6,000 sf, etc.), front/side/rear setbacks in Table 28‑32C, and max height (typically 35 ft; see § 28.93 for exceptions).
Historic-preservation effect: because the R‑TC districts explicitly aim to preserve neighborhood character, architectural approval (design review) under § 28.102 is commonly required for exterior changes; ADUs are allowed but subject to the ADU historic‑resource finding in § 28.72.10.

MP (Marsh Preservation) — § 28.52

Purpose: protect marsh/wetland habitat and tightly control development in Suisun Marsh; includes additional permit layers.
Typical permitted uses: marsh‑compatible uses in Table 28‑52A; development requires marsh development permits in addition to county permits.
Key standards: marsh development permit triggers, site plan, environmental findings, and architectural approval may be required; building permits still required and the Marsh permit may impose special conditions.
Historic-preservation effect: marsh‑area historic resources are subject to the same architectural review hooks, but proposals also face the marsh permit findings that may raise the standard of review where historic landscapes or structures are involved.

Policy Plan Overlay (-PP) (adopted via § 28.111 / policy plan overlay rules)

Purpose: custom overlay that can specify site‑specific standards (including architectural and sign standards) for parcels; added as a “‑PP” suffix on the zoning map. See the policy plan overlay rules and adoption procedures (refer to the policy plan overlay district and § 28.111).
Typical permitted uses & standards: established by the overlay’s ordinance and can include tailored historic‑compatibility design rules — i.e., a policy plan overlay is the county mechanism to create parcel‑level historic design standards if adopted.
Historic-preservation effect: an overlay can carry more prescriptive historic preservation rules (if the Board adopts them) — but the standard county materials supplied do not show an active county historic‑preservation overlay map. Not found in retrieved materials.

Quick Decision‑Relevant Table (most-used standards / references)

What an applicant needs to check	Key rule or limit	Code Reference
Whether architectural approval (design review) is required for external work	Architectural Approval required for many new or altered exteriors; building permit withheld until approval	§ 28.102
ADU on a parcel listed in the California Register	ADU / JADU not allowed unless Zoning Administrator finds “no significant adverse impact” on the historic resource	§ 28.72.10 (ADU rules)
R‑TC setback/lot area/design standards that affect historic properties	R‑TC development tables: lot sizes, setbacks, heights, ADU sizing in Table 28‑32C	§ 28.32.30 / Table 28‑32C
R‑R development/accessory building standards (rural historic residences)	Accessory building setbacks, height (35 ft typical), between‑structure distances	Table 28‑31C / § 28.31 series
Marsh/Resource area additional review	Marsh development permit required for development in Suisun Marsh; may add findings/conditions	§ 28.52 (Marsh Preservation)
Use of state historic rules for qualified properties	State Historical Building Code (CHBC) applies to qualified historical buildings/districts (alternative code/regulations)	CHBC 8‑1002.1 / 8‑1003

Checklist (what an applicant must satisfy for a project that affects a historic resource in unincorporated Solano County)

Confirm parcel zoning and underlying district(s) (see zoning maps; if boundary uncertain, Planning Commission will determine) — § 28.13.
Determine whether the property is on the California Register / qualified historic list; if yes, expect special ADU and review rules (see § 28.72.10).
Obtain a Zoning Clearance if verifying existing uses or nonconforming conditions before remodeling (see § 28.109).
Prepare application materials to satisfy architectural approval (elevations, materials, context) — required prior to building permit where § 28.102 applies.
If in Suisun Marsh or other resource district, prepare for marsh development permit and additional findings per § 28.52.
If seeking an ADU on a historic parcel, secure the Zoning Administrator’s written determination that the ADU will not have a significant adverse impact (ADU rules in § 28.72.10).
Verify compliance with lot/dimensional standards in the applicable district tables (R‑TC: Table 28‑32C; R‑R: Table 28‑31C).

Risks & Ambiguities

Issue	Why it matters	What to verify
No county historic overlay or county register found in supplied materials	May give applicants false expectation of a single county process or local landmark designation	Verify with County Planning whether a local historic survey or overlay exists beyond the code excerpts. Not found in retrieved materials.
Which changes trigger architectural approval	Architectural approval is referenced across districts but triggers differ by district/use	Verify at submittal with the Zoning Administrator whether the proposed work is subject to § 28.102; prepare elevations and materials.
ADU allowance on historic parcels — "written determination" test	The county requires a written Zoning Administrator finding that the ADU won’t cause a “significant adverse impact” — subjective standard can delay approval	Early consult with Planning; obtain the Zoning Administrator’s checklist or required cultural/historic report. See § 28.72.10.
Interaction with State CHBC vs county building code	CHBC offers alternatives but must be accepted/enforced by the county’s enforcing agency	Confirm whether the structure qualifies as a “qualified historical building” and whether the county will apply CHBC alternatives (see CHBC 8‑1002.1).
Parcel in Suisun Marsh with historic features	Marsh permit rules layer additional findings and public hearings which can affect timing and conditions	Confirm Marsh boundaries, and plan for the Marsh Development Permit per § 28.52.

Plain‑English Summary

Solano County handles historic preservation for unincorporated areas by folding historic‑sensitivity into existing rules: design review (architectural approval), district development standards (especially in R‑TC and R‑R), a specific ADU restriction when a property is listed on the California Register, and, when applicable, the State Historical Building Code. There is no single county “historic overlay” in the retrieved materials — instead, expect design review and discretionary findings to be the workhorses for protecting historic character.

Source References

Solano County Zoning Ordinance — Architectural Approval: § 28.102.
Solano County Zoning Ordinance — Residential / ADU rules (incl. “Impacts to Historical Properties”): § 28.72.10.
Solano County Zoning Ordinance — Residential‑Traditional Community development standards (Table 28‑32C): § 28.32.30 and Table 28‑32C.
Solano County Zoning Ordinance — Rural Residential development standards (Table 28‑31C; R‑R): § 28.31 series / Table 28‑31C.
Solano County Zoning Ordinance — Marsh Preservation (MP District) and marsh development permits: § 28.52.
Solano County Zoning Ordinance — Zoning Clearance procedures: § 28.109.
Solano County Zoning Ordinance — Policy Plan Overlay (‑PP) and adoption procedures (see adoption by ordinance / § 28.111 references).
California Historical Building Code (CHBC) — application to qualified historic buildings/districts (e.g., 8‑1002.1 / 8‑1003).

(If you want direct PDF or ordinance page links I can pull the exact local code web URLs for each § — tell me which § you want the live document link for and I’ll fetch it.)

Sources

Retrieved passages

Solano County Zoning Code (Section 28-111) Medium relevance
CBC § 102 (Chapter 28) Medium relevance
Solano County Zoning Code (Section 28.73.30) Medium relevance
Solano County Zoning Code (Section 11-111) Medium relevance
CBC § 380 (Chapter 28) Medium relevance
Solano County Zoning Code (§ 65915) Medium relevance
Solano County Zoning Code (Section 28.01) Medium relevance
Solano County Zoning Code (Chapter 28) Medium relevance
CBC § 18955 (Section 18955) Medium relevance
CBC § 18954 (Section 18954) Medium relevance
Solano County Zoning Code (Section 11-111) Medium relevance
CBC § 4 (Section 28.01) Medium relevance
CBC § 8 (chapter is) Medium relevance
Solano County Zoning Code (§ 66314) Medium relevance
CBC § 8 (SECTION 8-1001) Medium relevance
CBC § 8 (SECTION 8-301) Medium relevance
Solano County Zoning Code (§6) Medium relevance
CBC § 2 (Section 28-93) Medium relevance
Solano County Zoning Code (Section 28.102) Medium relevance
CBC § 2 (Section 28.01.) Medium relevance
Solano County Zoning Code (Section lists) Medium relevance

Cited sections

Solano County Zoning Ordinance — Architectural Approval: **§ 28.102**. (§ 28.102)
Solano County Zoning Ordinance — Residential / ADU rules (incl. “Impacts to Historical Properties”): **§ 28.72.10**. (§ 28.72.10)
Solano County Zoning Ordinance — Residential‑Traditional Community development standards (Table 28‑32C): **§ 28.32.30** and Table 28‑32C. (§ 28.32.30)
Solano County Zoning Ordinance — Rural Residential development standards (Table 28‑31C; R‑R): **§ 28.31** series / Table 28‑31C. (§ 28.31)
Solano County Zoning Ordinance — Marsh Preservation (MP District) and marsh development permits: **§ 28.52**. (§ 28.52)
Solano County Zoning Ordinance — Zoning Clearance procedures: **§ 28.109**. (§ 28.109)
Solano County Zoning Ordinance — Policy Plan Overlay (‑PP) and adoption procedures (see adoption by ordinance / § 28.111 references). (§ 28.111)
California Historical Building Code (CHBC) — application to qualified historic buildings/districts (e.g., **8‑1002.1 / 8‑1003**).
SolanoCounty_ZoningCode.md
2025 California Historical Building Code.md

Frequently asked questions

Who decides whether I need architectural approval for work on an old house in unincorporated Solano County?

The Zoning Administrator and Planning Commission administer architectural approval; the county’s rules require architectural approval where called out in a district or use table — see § 28.102 for scope and procedure. Expect the Zoning Administrator to require elevation drawings and materials to determine compatibility.

Can I add an ADU to a house that’s listed on the California Register?

Not automatically. The ADU rules require that a secondary or junior ADU not be allowed on a property listed on the California Register unless the Zoning Administrator makes a written determination that the ADU would not have a significant adverse impact on the historic resource; see the ADU provisions in § 28.72.10.

Is there a county historic overlay or local landmark register I must apply to?

Not in the materials provided — the code includes overlays (policy plan overlays) that can carry special standards, but I did not find a dedicated county historic overlay or county landmark register in the retrieved ordinance excerpts. Verify with the Planning Division if a local inventory or overlay exists for your parcel. Not found in retrieved materials.

If my property is in a Suisun Marsh area, does that change the review for historic work?

Yes. Development in the Marsh Preservation District requires a marsh development permit in addition to county permits, and marsh permit findings and conditions can affect historic resources in the marsh; see § 28.52. Expect extra timing, public notice, and likely additional environmental review.

What rules govern setbacks, height and lot coverage for older houses when I propose changes?

Apply the district’s development standards (e.g., Table 28‑32C for R‑TC; Table 28‑31C for R‑R). These tables specify minimum lot area, setbacks, and height limits; architectural approval under § 28.102 can also condition design elements. Check the specific table for your zoning suffix (R‑TC‑4, R‑TC‑6, R‑R‑5, etc.).

If I want to demolish a garage on a historic parcel to build an ADU, what happens?

Under state ADU guidance local agencies must coordinate demolition and ADU permits together; locally, the ADU rules require the Zoning Administrator’s determination for properties listed on the California Register. If the parcel is architecturally/historically significant the county may require additional notice or review as part of architectural approval (see § 28.72.10 and state ADU guidance).

What code applies if I’m repairing/rehabbing a qualified historic building and I need alternatives to current Title 24 rules?

Qualified historic buildings may use the California Historical Building Code (CHBC) alternative provisions; see CHBC sections such as 8‑1002.1/8‑1003 and coordinate with the county’s enforcing agency for acceptance and application of CHBC alternatives.

Do nonconforming-use rules protect an older structure from being forced into compliance if I repair it?

Nonconforming use and structure rules limit what changes can be made without additional permits; Solano County’s nonconforming provisions and zoning‑clearance rules apply (see § 28.114 for nonconforming uses and § 28.109 for zoning clearances). Repairs are often allowed but expansions or substantial alterations can trigger further review.

Who issues the written determination about “significant adverse impact” for an ADU on a historic parcel?

The county Zoning Administrator makes the written determination required by the ADU rules (see § 28.72.10). If you are preparing an ADU application on a potentially historic parcel, request a pre‑application meeting to learn what documentation the Administrator will require.

Where can I get the objective design guidelines the county uses for architectural approval?

The code requires architectural approval under § 28.102 but the specific objective standards are included in district development standards, tables (e.g., Table 28‑32C, Table 28‑31C), and any overlay or policy plan text. Request the applicable district tables and any overlay ordinance from the Planning Division; the code references architectural standards repeatedly in the district chapters.

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