San Carlos — Nonconforming Uses

Last reviewed: July 2, 2026

Overview

San Carlos treats nonconforming uses, structures, and lots as legally established features that no longer meet current zoning rules but may continue under limits designed to protect public health and the General Plan. The full local rule set is in Chapter 18.19 (Nonconforming Uses, Structures, and Lots); key operational rules appear in § 18.19.030 through § 18.19.100.

Below is a San Carlos–specific reference you can use to check whether a use or building on your property can continue, be repaired, be enlarged, or must be discontinued.

Note: this page covers only the San Carlos zoning/planning ordinance (Title 18). For parking, see the city parking rules; for design approvals, see the design-review rules; for ADU standards and state ADU interaction see the ADU chapter and state law links cited below.

• First internal links in the prose:
  • San Carlos parking
  • San Carlos Development Standards
  • San Carlos Design Review
  • San Carlos Overlay Districts
  • San Carlos ADUs
  • California Building Standards Code
  • San Carlos Zoning

What the ordinance says (high level)

• Any use, structure, or lot lawfully existing on the effective date of the zoning rules or a later amendment that does not meet current rules is a nonconformity and may only continue subject to Chapter 18.19. See § 18.19.030(A).
• A nonconforming lot that is a lot of record may still be used as a building site, subject to the Code and any needed variance. See § 18.19.030(B).
• Nonconforming uses generally cannot be enlarged or changed to another nonconforming use without approval; expansion and substitutions trigger administrative discretionary review (minor use permit, use permit, or Planning and Transportation Commission as specified). See § 18.19.060–18.19.070.
• Repairs and restoration after damage are allowed up to a 50% cost threshold; above 50% of appraised value triggers compliance with current rules unless specified exceptions apply. See § 18.19.080(A–B).
• Abandonment rules: nonconforming commercial or other non-residential uses that are vacated or otherwise inactive for six months are considered abandoned; resumption requires a conditional use permit and specific findings. See § 18.19.090.

Decision-relevant summary table (quick lookup)

District-by-district (how nonconforming rules interact with common San Carlos districts)

Below are the primary San Carlos zoning districts most often encountered in nonconformity questions. For each district I list the district name in bold, its purpose (from the Code), typical permitted uses (from the use tables), the most relevant dimensional or development standard sources you should check, and where that district commonly applies in the city.

Note: Chapter 18.19 applies citywide to nonconformities in all districts; the district references below point you to the district-specific use lists and development standards that determine whether a proposed change will be compliant. See § 18.19.020 and the district tables.

RS-3 (Single-family residential)

• Purpose: preserve single-unit residential character and lot-scale development. See general RS district rules in the base district tables.
• Typical permitted uses: single-family dwelling, accessory uses (home occupations, ADUs subject to § 18.23.210), limited public/semi‑public uses where noted. See the RS use table entries.
• Key dimensional standards / where to look: front/side/rear setbacks, lot coverage, and height standards are in the RS development tables and small-lot tables (e.g., Table 18.04.100-G for small-lot single-unit projects). If your lot is small or in a small‑lot subdivision consult Table 18.04.100‑G for front/side/rear specifics.
• How nonconforming rules apply: existing nonconforming setbacks or coverage can be maintained for residential additions so long as the addition complies with the chapter rules and no existing setback less than 3 ft is treated as legal for new purposes (§ 18.19.050(D)(2–3)).

RS-6 (Single-family residential, smaller lots / different density)

• Purpose & typical uses: similar to RS-3, but with different lot-size/density intent; uses and accessory standards are in the RS tables.
• Key standards: check the RS table for exact minimum lot size, setbacks, and landscaping requirements; any addition to a nonconforming residential structure must meet the current setbacks at time of application except where maintenance of existing setback is allowed under § 18.19.050(D).

RM-20 (Multifamily residential)

• Purpose: higher density residential sites and multifamily housing. Typical uses include multifamily units, supportive housing types, and related accessory uses. Use and supplemental standards appear in Table 18.04.050-2.
• Key dimensional standards: lot coverage (e.g., 65% for RM-20), open space and landscaping minima, maximum building separation and parking location rules are in the RM development tables; transitional standards apply where RM abuts RS districts (setbacks and stepbacks to match RS height at the property line). See the RM tables and transitional provisions.
• Nonconforming interaction: Nonconforming multifamily buildings damaged ≤50% may be rebuilt up to previous size and unit count subject to a zoning clearance or conditional permit as specified in § 18.19.080.

MU-DC-100 / MU-D-100 (Mixed‑use / downtown / corridor districts)

• Purpose: allow mixed residential and commercial development with district-specific density and frontage rules. See MU district development tables (Table 18.05.030-1 and building placement Table 18.05.030-2).
• Typical permitted uses: ground-floor retail/service (with some limits on ground-floor uses on specific frontages), upper-story residential, offices. See MU use tables and special limitations (e.g., restrictions on certain ground-floor uses on Laurel Street, San Carlos Ave, or El Camino Real).
• Key dimensional standards: frontage setbacks vary by street (Laurel Street and El Camino Real frontage rules are stricter — see Table 18.05.030-2), maximum density and story counts per MU district are in Table 18.05.030-1.
• Nonconforming interaction: a nonconforming commercial use in MU districts may be continued but enlargement, change of use or ground-floor alterations must comply with § 18.19 and often trigger design-review, parking and use-permit procedures. See § 18.19.040–.070.

IA / IL / IH / IP (Industrial / Business Park districts)

• Purpose & typical uses: industrial, warehousing, light manufacturing, and utilities as listed in the industrial use tables. Certain conditional use limitations and adjacency rules apply; see the industrial tables and Chapter 18.14A for special industrial area rules.
• Key standards: industrial districts have conditional use limitations (e.g., proximity to residential triggers additional review); review the industrial use summary and Chapter 18.14A where indicated.
• Nonconforming interaction: nonconforming industrial uses are governed by Chapter 18.19; where a change of use is proposed that increases nuisance potential the Code can require permit approvals or abatement actions under § 18.19.100 and enforcement chapters.

P / PK / OS (Public, parks, open space)

• Purpose: public facilities, parks, and open spaces with specific development standards (Table 18.08.030).
• Typical permitted uses: parks, institutional, and public safety facilities; uses limited to preserve open-space character.
• Nonconforming interaction: public or semi-public structures that became nonconforming remain subject to Chapter 18.19; consult the P/PK/OS tables for setbacks and required landscaping when considering repair or modification.

Practical guidance and interpretation tips

• Establish lawfulness: To claim nonconforming status you must be able to show the use/structure was legally established prior to the applicable ordinance or amendment — check building permits, recorded lot descriptions, and business licensing records. The Code explicitly treats lawful pre-existing items as nonconforming under § 18.19.030.
• Repairs vs. reconstruction: Small repairs and interior maintenance are generally allowed without triggering conformity; structural repairs or rebuilds that exceed fifty percent (50%) of appraised value require compliance with current standards except where the Code provides exceptions; see § 18.19.040(C) and § 18.19.080. You should expect the City to order an appraisal to establish the 50% threshold.
• Additions and lot coverage: If your proposed addition increases lot coverage above current maximums you will need a variance (Chapter 18.32) — Chapter 18.19.050(E) notes that such increases require variance approval.
• Expansions and changes of use: Expansion of a nonconforming use, or changing it to another nonconforming use, requires a use permit or minor use permit and specific findings (see § 18.19.060–.070). Expect findings about compatibility with the General Plan and impacts on neighbors.
• ADUs on nonconforming lots/structures: An ADU may be developed on a lot with a nonconforming single-unit dwelling in accord with the ADU chapter and Chapter 18.19.050(C) (and note state ADU law constraints). See San Carlos ADU standards (Table 18.23.210) and the Code cross‑references.

Checklist (what an applicant must satisfy to work with a nonconforming use/structure)

• Demonstrate the use or structure was lawfully established before the controlling ordinance or amendment (document permits, recorder records, business licenses). See § 18.19.030.
• Confirm whether proposed work is maintenance/repair (allowed) vs. structural repair/rebuild (may be limited by 50% threshold). See § 18.19.040(B–C) and § 18.19.080.
• If proposing expansion of use or building area, prepare application for a minor use permit or use permit (Zoning Administrator or Planning & Transportation Commission), with required findings addressing compatibility and General Plan consistency. See § 18.19.060–.070.
• If addition increases lot coverage or violates development standards, prepare a variance application (Chapter 18.32) or other modification request. See § 18.19.050(E).
• If damage occurred, get a professional appraisal to determine whether repairs exceed 50% replacement value; if >50% plan to bring structure into current Code compliance per § 18.19.080(B).
• Verify parking, loading, and landscape requirements are met or addressed (parking standards are in Chapter 18.20). Note: a use is not nonconforming solely because it fails to meet some parking/landscape dimension standards — see § 18.19.030(A) and Chapter 18.20 cross‑references.

Risks & Ambiguities

Plain-English Summary

If your building, parking, or business in San Carlos predates a zoning change, you can usually keep operating — but you generally cannot enlarge the space or change its use without permission, structural fixes that cost more than half the building’s value will trigger current code requirements, and if the use sits vacant for six months it can lose its protected status; see Chapter 18.19 for the exact rules.

Source References

• San Carlos Municipal Code, Chapter 18.19 (Nonconforming Uses, Structures, and Lots), §§ 18.19.010–18.19.100 (purpose, applicability, continuation, additions, expansion, changes, repair/replacement, abandonment, abatement).
• San Carlos Development Standards and district tables: Tables for MU districts (Table 18.05.030 series), RM district tables, and Small Lot Single-Unit standards (Table 18.04.100‑G). See Table 18.05.030-2 and Table 18.04.100‑G for setbacks and lot-coverage examples.
• ADU development standards and interaction with nonconforming residential lots: Table 18.23.210(E)(4) and § 18.19.050(C).
• Parking chapter and nonconforming parking cross‑reference: Chapter 18.20 and the nonconforming use exclusions in § 18.19.030(A).
• Enforcement and nuisance abatement provisions that can supersede nonconforming protections: Chapter 18.39 (Enforcement), including § 18.39.020–.070.

Retrieved passages

• San Carlos Zoning Code (chapter apply) High relevance show source text
• San Carlos Zoning Code (Chapter 18.19) High relevance show source text
• San Carlos Zoning Code (Chapter 18.40) High relevance show source text
• CBC § 1 (section shall) High relevance show source text
• San Carlos Zoning Code (Section 18.20.030) High relevance show source text
• CBC § 4 (Chapter 18.32) High relevance show source text
• CBC § 4 (§ 4) High relevance show source text
• San Carlos Zoning Code (§ 4) High relevance show source text
• San Carlos Zoning Code (Section 18.05.030) High relevance show source text
• San Carlos Zoning Code Medium relevance show source text
• San Carlos Zoning Code (Chapter 18.14A.) Medium relevance show source text
• San Carlos Zoning Code Medium relevance show source text
• San Carlos Zoning Code (§ 66314) Medium relevance show source text
• CBC § 66314 (§ 66314) Medium relevance show source text

Cited sections

• San Carlos Municipal Code, Chapter **18.19** (Nonconforming Uses, Structures, and Lots), §§ **18.19.010–18.19.100** (purpose, applicability, continuation, additions, expansion, changes, repair/replacement, abandonment, abatement).
• San Carlos Development Standards and district tables: Tables for MU districts (Table 18.05.030 series), RM district tables, and Small Lot Single-Unit standards (Table 18.04.100‑G). See Table **18.05.030-2** and Table **18.04.100‑G** for setbacks and lot-coverage examples.
• ADU development standards and interaction with nonconforming residential lots: Table **18.23.210(E)(4)** and **§ 18.19.050(C)**. (§ 18.19.050)
• Parking chapter and nonconforming parking cross‑reference: Chapter **18.20** and the nonconforming use exclusions in **§ 18.19.030(A)**. (chapter and)
• Enforcement and nuisance abatement provisions that can supersede nonconforming protections: Chapter **18.39** (Enforcement), including § **18.39.020–.070**.
• SanCarlos_ZoningCode.md

• Official San Carlos code library