Carson — Historic Preservation

Last reviewed: July 1, 2026

Overview

This page summarizes what the Carson zoning and planning ordinance says about historic preservation, including how historic designations interact with accessory dwelling units (ADUs), second primary units, urban lot splits, and design-review/overlay rules. It interprets the Carson Municipal Code (CMC) rules that directly reference historic districts, historic resources, or landmarks and points to the specific controlling sections you must check when planning work on or near a historically designated property. For general building rules (Title 24) see the California Building Standards Code link below.

What the code actually requires — short list

• Accessory dwelling units on properties determined historic are processed ministerially, but if the property is listed on the California Register the ADU must meet the Secretary of the Interior Standards; see § 9122.1.
• Second primary units / two-unit developments are prohibited on parcels located in a historic district or on property listed in the State Historic Resources Inventory or designated as a local landmark; see § 9128.83(F).
• Urban lot splits (two-parcel splits) may not be used on parcels located in a historic district or on properties listed on the State Historic Resources Inventory or designated as a City/County landmark; see § 9210.4(E).
• Projects in a D (Design Overlay) area are subject to Site Plan and Design Review (the City’s design-review procedure) and the overlay expressly contemplates preservation of areas with historical or cultural interest; see § 9126.9(B) and § 9156.9 requiring conformity with § 9172.23 (Site Plan & Design Review).

(Internal links used where topics are first mentioned: Carson zoning & planning overview, Carson Zoning, Carson ADUs, Carson Design Review, Carson Overlay Districts, Carson Parking, California Building Standards Code.)

District-by-district breakdown — how historic rules apply in each common Carson zone

Note: below the district names and key local numeric standards are shown in bold. Always cross-check the property zone on the City's zoning map and verify parcel-specific requirements with City staff.

RS (Single-Family Residential)

• Purpose & where it applies: The RS zone is the default single-family residential zone used across neighborhoods; permitted uses and density rules are summarized in CMC § 9121.1.
• Typical permitted uses: Single-family dwellings, Accessory dwelling units (ADUs) are allowed in RS (see table of permitted uses).
• Historic-specific impacts:
  • Second primary units / two-unit developments may be allowed in limited circumstances (ministerial or limited review) but are specifically prohibited on parcels inside a historic district or on City/County/state-listed historic properties — see § 9128.83(F).
  • ADUs on historic properties are permitted but processed ministerially; if the property is listed on the California Register, the ADU must meet the Secretary of the Interior Standards (see § 9122.1).
• Key dimensional guidance for ADUs: 4 ft side/rear minimum setback (conversion exceptions apply); detached ADU max 1,200 sq ft, height 16 ft (one story), and attached/attached-max rules per § 9122.1.

RA (Residential Agricultural)

• Purpose & where it applies: Agricultural/residential fringe; uses and standards summarized in CMC § 9113.1 and the RA entries in the permitted-uses table.
• Typical permitted uses: Single-family dwellings, ADUs (allowed per ADU rules).
• Historic-specific impacts: Same cross-cutting rules as RS for ADUs and for restrictions on second primary units and urban lot splits where a historic designation is present (see § 9122.1, § 9128.83(F), § 9210.4(E)).

RM (Multiple-Family Residential)

• Purpose & where it applies: Higher-density residential areas; multiple-family developments are permitted subject to development standards and design review for some projects.
• Typical permitted uses: Multiple-family dwellings, ADUs (where allowed by parcel type), and development often requires Site Plan and Design Review for multi-unit projects.
• Historic-specific impacts:
  • ADU conversions on historic multifamily properties follow the ADU ministerial rules but may be limited by the requirement to meet historic preservation standards if the structure/property is designated/listed; see § 9122.1.
  • Projects converting, subdividing, or substantially altering historic multi-family buildings will often trigger Site Plan & Design Review (CMC § 9172.23) and thus scrutiny of exterior changes.

CA (Commercial, Arterial / Corridor Commercial)

• Purpose & where it applies: Commercial corridors and auto-oriented commercial areas; see CA-specific development rules (Part 6 and 9 references).
• Typical permitted uses: Retail, vehicle dealerships (special rules), and other commercial uses.
• Historic-specific impacts: If commercial property lies within a D (Design Overlay) or a locally designated historic area, exterior changes and signs are controlled by development plans reviewed under § 9172.23; vehicle dealerships and other CA uses have overlay-specific controls (see § 9136.9, § 9172.23).

MU‑CS (Mixed-Use – Carson Street Corridor)

• Purpose & where it applies: Downtown/mixed-use core; the zone emphasizes pedestrian character and design-quality standards. MU-CS projects are routinely subject to Site Plan & Design Review.
• Typical permitted uses: Mixed-use residential/commercial, with residential projects frequently subject to design review.
• Historic-specific impacts: Existing historic buildings in this area will typically be required to comply with a Development Plan under § 9172.23, which is the City’s avenue for reconciling preservation and redevelopment.

D (Design Overlay) (Overlay district)

• Purpose & where it applies: The D (Design Overlay) is used to regulate design details and to preserve areas with scenic, historic, cultural, or scientific interest. § 9126.9(B) explicitly lists preservation of areas of historical interest among overlay goals.
• How it affects historic work: All post-designation development in a D area must conform to approved development plans and require Site Plan & Design Review (CMC § 9172.23); permits for significant exterior changes will not be issued unless in conformance with approved plans (see § 9156.9, § 9136.9, and § 9172.23).

Quick decision-relevant standards (table)

Practical guidance & synthesis (plain-English interpretation)

• If your property is within a City-designated historic district, is listed as a City/County landmark, or appears on the State Historic Resources Inventory, expect that many otherwise-normal zoning actions (second primary units, urban lot splits) are restricted or prohibited: see § 9128.83(F) and § 9210.4(E). Verify designation early with the Planning Department.
• If you want to put an ADU on a historic property, Carson’s code allows ministerial ADU approvals even when the primary structure is historic; however, if the property is listed on the California Register, the ADU design must meet the Secretary of the Interior Standards — that is a material, non-waivable standard in Carson’s ADU rules; see § 9122.1.
• If the property sits inside a D (Design Overlay), expect mandatory design-review rules that can require an approved Development Plan before issuance of permits for significant exterior work; see § 9126.9 and § 9156.9. Early pre-application review with the Director/Planning staff is recommended.
• Don’t confuse building-code relief for historic structures (California Historical Building Code or variances under Title 24) with zoning allowances: Carson’s zoning specifies when historic properties trigger special zoning rules (ADU ministerial path and design-review triggers), while building-code relief is a separate process (refer to the California Building Standards Code). For zoning, see § 9122.1, § 9128.83, § 9210.4, and § 9172.23.

Checklist — what an applicant must satisfy (pre-application)

• Confirm whether the property is within a historic district, designated a City/County landmark, or appears on the State Historic Resources Inventory (Verify with Planning). See § 9128.83(F) and § 9210.4(E).
• For an ADU, prepare plans that meet ADU dimensional standards: max sizes, 4 ft side/rear setbacks for new construction, 16 ft height for detached ADU (one story), parking plan (max 1 space), and deed restriction forms; see § 9122.1 and § 9162.21.
• If the property is listed on the California Register, prepare documentation that the ADU or rehabilitation will conform to the Secretary of the Interior Standards (per § 9122.1).
• If work is in a D (Design Overlay) area or the project is a larger residential/commercial change, expect to submit a Development Plan for Site Plan & Design Review under § 9172.23 and coordinate on exterior materials and screening standards.
• Check whether the project is an urban lot split or second-unit application; if so, verify it is not within a historic district or on a listed historic property (urban splits are disallowed on historic parcels per § 9210.4(E); second units disallowed per § 9128.83(F)).

Risks & Ambiguities

Plain-English Summary

If your Carson property is inside a historic district, listed as a local landmark, or on the State Historic Resources Inventory, some common zoning moves (second primary units, urban lot splits) are off-limits, and ADUs are allowed only under stricter historic-preservation rules; projects in design-overlay areas must clear design review. Verify the parcel’s historic status with Planning before you design. See § 9122.1, § 9128.83(F), § 9210.4(E), and § 9172.23.

Source References

• CMC § 9122.1 (Accessory dwelling units — ministerial approval on historic properties; Secretary of the Interior Standards requirement) — § 9122.1.
• CMC § 9128.83 (Second primary units and two-unit developments — prohibition in historic districts / listed properties) — § 9128.83(F).
• CMC § 9210.4 (Urban lot split parcel requirements — prohibition in historic districts / listed properties) — § 9210.4(E).
• CMC § 9126.9 and § 9156.9 (D (Design Overlay) purposes and design-review requirement) — § 9126.9(B), § 9156.9.
• CMC § 9172.23 (Site Plan and Design Review — procedure and findings) — § 9172.23.
• Permitted uses / zone table entries for RA, RS, RM and ADU allowances — permitted uses table and zone summaries.
• ADU development standards (sizes, setbacks, parking) — § 9122.1 (E) and related subsections.
• Design overlay and CA zone site-design rules (screening, undergrounding utilities) — § 9136.9, § 9136.8.

Retrieved passages

• CBC § 10 (§ 10) Medium relevance show source text
• CBC § 16 (§ 16) Medium relevance show source text
• CMC § 10 (Chapter 12.75) Medium relevance show source text
• CMC § 16 (§ 16) Medium relevance show source text
• Carson Zoning Code (title to) Medium relevance show source text
• CMC § 9402 (§ 9402) Medium relevance show source text
• CMC § 9126.91 Medium relevance show source text
• Carson Zoning Code (§ 2) Medium relevance show source text
• CMC § 9138.15 Medium relevance show source text
• Carson Zoning Code Medium relevance show source text
• Carson Zoning Code (§ 65915) Medium relevance show source text
• CMC § 6 (§ 6) Medium relevance show source text
• CMC § 4 (§ 4) Medium relevance show source text
• CBC § G106 (SECTION G106) Medium relevance show source text
• Carson Zoning Code (title to) Medium relevance show source text
• CMC § 6 (Section or) Medium relevance show source text
• Carson Zoning Code (Chapter in) Medium relevance show source text
• CMC § 9126.8 (§ 9126.8.) Medium relevance show source text
• CFC § 18 (§ 18) Medium relevance show source text
• CMC § 9156.9 (§ 9156.9.) Medium relevance show source text
• CFC § 9182.24 (§ 9182.24.) Medium relevance show source text
• CMC § 9 (section shall) Medium relevance show source text
• CMC § 7 (Section are) Medium relevance show source text

Cited sections

• CMC § 9122.1 (Accessory dwelling units — ministerial approval on historic properties; Secretary of the Interior Standards requirement) — **§ 9122.1**. (§ 9122.1)
• CMC § 9128.83 (Second primary units and two-unit developments — prohibition in historic districts / listed properties) — **§ 9128.83(F)**. (§ 9128.83)
• CMC § 9210.4 (Urban lot split parcel requirements — prohibition in historic districts / listed properties) — **§ 9210.4(E)**. (§ 9210.4)
• CMC § 9126.9 and § 9156.9 (D (Design Overlay) purposes and design-review requirement) — **§ 9126.9(B)**, **§ 9156.9**. (§ 9126.9)
• CMC § 9172.23 (Site Plan and Design Review — procedure and findings) — **§ 9172.23**. (§ 9172.23)
• Permitted uses / zone table entries for **RA**, **RS**, **RM** and ADU allowances — permitted uses table and zone summaries.
• ADU development standards (sizes, setbacks, parking) — **§ 9122.1 (E)** and related subsections. (§ 9122.1)
• Design overlay and CA zone site-design rules (screening, undergrounding utilities) — **§ 9136.9**, **§ 9136.8**. (§ 9136.9)
• Carson_ZoningCode.md

• Official Carson code library