Suisun City — Nonconforming Uses

Last reviewed: July 2, 2026

Overview

This page summarizes how Suisun City treats nonconforming uses, nonconforming structures, and nonconforming lots under the local zoning ordinance (Title 18, Zoning). It explains the key standards that let a previously lawful use remain (or be lost), how repairs and reconstruction are limited, and how those rules interact with district standards such as setbacks, lot coverage, and ADU rules. All requirements below are grounded in the Suisun City Municipal Code and cited to the controlling sections.

Before you read: if your question touches parking, setbacks/development standards, design review, overlay districts, or ADUs, see the linked city topics as you proceed — they affect how nonconforming situations are evaluated: Suisun City Parking, Suisun City Development Standards, Suisun City Design Review, Suisun City Overlay Districts, Suisun City ADUs. If construction touches life-safety systems, the California Building Standards Code still applies.

What Suisun City’s code says (plain terms + controlling §§)

• Legal nonconforming conditions are allowed to continue but with limits:
  • A lawful use of land that was legal when the zoning ordinance took effect may continue but cannot be enlarged, increased or extended beyond the area it occupied at adoption. See § 18.68.010 .
  • A lawful building use existing at adoption may continue even if it does not meet current standards. See § 18.68.020 .
• Any use that requires a discretionary use permit is treated as nonconforming until the permit is actually obtained. See § 18.68.030 .
• If a nonconforming building is damaged or destroyed to more than 60% of its fair market value (as assessed by the county assessor for that fiscal year), it loses its nonconforming status and must be rebuilt to current code/siting standards. See § 18.68.040 .
• Abandonment: if the operation of a nonconforming use stops for a continuous six months, it is presumed abandoned and the use rights terminate; the property must thereafter conform to current use rules. See § 18.68.050 .
• Repairs and maintenance: ordinary maintenance and repairs are permitted, but no structural alterations or additions are allowed and repairs in any single 12‑month period shall not exceed 25% of actual value (there are HUD/DSBG exceptions). See § 18.68.060 .
• Buildings already under construction when the ordinance became effective may be completed per the original lawful plans. See § 18.68.070 .

Note the code’s local definition of “legal nonconforming use” which appears in the yard/definitions sections: a use, structure, or condition that was legal when installed but no longer complies with current code. See § 18.36.070 for definitions and “grandfathering” language.

District-by-district (how nonconforming treatment matters where your property sits)

Below are Suisun City zoning districts with the most decision-relevant standards a practitioner will pair with the nonconforming rules. For permitted uses and specific numeric standards consult the listed tables and sections.

• RL (Low‑Density Residential)

  • Purpose: single‑family character at low densities. Typical permitted uses: single‑family dwellings, accessory buildings, small community care facilities (see Table 18.08.02). See § 18.08.050 and Table 18.08.02.
  • Key dimensional standards (from Table 18.31.01 / § 18.31.005): minimum lot area 3,600 sf, front setback 10–20 ft, max lot coverage 40%, max height 35 ft.
  • Where it applies: low‑density neighborhoods shown on the zoning map; nonconforming single‑family structures may continue but cannot be expanded in area per § 18.68.010.

• RM (Medium‑Density Residential)

  • Purpose: duplexes, small multi‑family. Permitted uses include two‑family, accessory dwellings, and certain multi‑family with administrative or conditional review. See Table 18.08.02 and § 18.08.070.
  • Key standards: min lot area 1,800 sf, front setback 10–20 ft, max lot coverage 80%, height 35 ft. ADU side/rear setbacks 4 ft minimum. See § 18.31.005.

• RH1 and RH2 (High‑Density Residential 1 & 2)

  • Purpose: higher density multi‑family and mixed‑residential uses. Typical permitted uses include multi‑family dwellings, accessory dwellings, and some community facilities. See Table 18.08.02.
  • Key standards: RH1 and RH2 allow 0–15 ft front minimums (flexible), max height 55 ft, and lot coverage up to 80%. ADU minimum side/rear 4 ft applies. See § 18.31.005.
  • Note: nonconforming multi‑unit buildings damaged over 60% of value lose their nonconforming siting/use rights under § 18.68.040.

• RMU (Residential Mixed‑Use)

  • Purpose: ground‑floor nonresidential with residential above; density 10–45 du/ac and FAR 0.3–1.0. See § 18.08.050 and Table 18.08.01.
  • Key standards: front setback 0–15 ft, height up to 55 ft, lot coverage 80%; nonconforming commercial uses that predate rezoning may continue but are limited by § 18.68.010–.070.

• Commercial and Industrial (examples)

  • The code contains multiple commercial/industrial districts (see Table 18.06.01 and commercial use tables). Typical district labels in the code include commercial and manufacturing zones; permitted uses and parking are spelled out in Tables 18.08.xx and 18.42.xx. A nonconforming commercial use remains allowed only under the same limits (no enlargement, abandonment rules, repair cap). See Tables and chapters referenced in § 18.06.010, Tables in § 18.08.02, and § 18.68.010–.070.

Table: Quick reference to the most decision‑relevant rules and where to confirm them

Practical guidance and interpretation (how this plays out)

• If you claim a property use or building is legally nonconforming, the city will expect proof it was lawful when established (permits, old maps, business licenses). The code’s definition of legal nonconforming use and “grandfathering” language is recorded in the definitions and yard chapter. See § 18.36.070.
• You can make ordinary repairs. You cannot erect an addition or structurally alter a nonconforming building to increase nonconforming aspects without losing the protection; the repair cap of 25% of value per year is enforced administratively. See § 18.68.060.
• If your structure is substantially damaged, the 60% threshold uses the county assessor’s fair market value for that fiscal year — get a written assessor value if you are near the threshold. See § 18.68.040.
• For ADUs, Suisun City’s local ADU rules provide ministerial (no‑hearing) approval when the ADU meets code and are explicit about small setbacks such as 4 ft side/rear for ADUs; ADU ministerial rules interact with nonconforming conditions and State ADU law — verify with the ADU section § 18.30.170 and the ADU ministerial subsections. See § 18.30.170.
• For SB‑9 (two‑unit ministerial lot splits) the city states the correction of nonconforming zoning conditions is not required as a condition of ministerial approval. See SB‑9 provisions in § 18.08.095 / related SB‑9 text.
• Always coordinate nonconforming use claims with the development services director; the code gives the director authority to investigate and request evidence and expert reports (costs for expert review may be charged to the property owner if the nonconformance is confirmed). See administrative enforcement provisions in the code.

Checklist (what an applicant must supply / satisfy when seeking to preserve or modify a nonconforming use)

• Proof the use/structure was lawful when established (old permits, tax records, photos) — verify claim against the definition of legal nonconforming use in § 18.36.070.
• Site plan showing the exact area occupied at the time the ordinance changed (to show no enlargement per § 18.68.010).
• Evidence of continuous operation (to refute a 6‑month abandonment claim under § 18.68.050).
• Contractor/repair estimates and a valuation (if proposing repairs) to confirm repairs will not exceed 25% of actual value in any one‑year period (§ 18.68.060).
• If the building was damaged, an appraisal or assessor value to determine the 60% threshold in § 18.68.040.
• If proposing changes that would conflict with district standards (setbacks, coverage, height), demonstrate compliance with or seek a variance per the city's variance chapter; if it’s an ADU, comply with § 18.30.170 ADU ministerial rules.

Risks & Ambiguities

Plain‑English Summary

If your home or business in Suisun City was legal under old rules but no longer meets the current zoning, you can usually keep using it — but you cannot expand it, if it stops operating for six months you lose the right, major damage (more than 60% of assessed value) forces reconstruction to current code, and only limited repairs are allowed (no structural additions and repairs capped at 25% of value per year). Check the precise numeric setbacks, coverage, and ADU rules in the residential tables and ADU section before changing anything. See § 18.68.010–.070 and the residential development standards in § 18.31.005.

Information Gaps

• A full list of all commercial and industrial zone labels and every numeric standard for each district can be found in the city's full Table 18.06.01 and the various use tables; the excerpts supplied contained the residential tables and selected use tables but not every commercial district column. Verify the precise commercial/industrial zone label for your parcel and the associated table. Not found in retrieved materials: a consolidated single page listing every zone label with full numeric standards for non‑residential districts.
• Parcel‑specific determinations (whether a particular structure is “legal nonconforming”) require archival permit records and sometimes assessor/parcel history; the code gives the tests but not parcel histories. Verify with the jurisdiction.

Source References

• Suisun City Municipal Code, Chapter 18.68, Nonconforming Uses — § 18.68.010 through § 18.68.070.
• Suisun City Municipal Code, Chapter 18.31 and Table 18.31.01, Development Standards for Residential Zones (RL, RM, RH1, RH2, RMU) — § 18.31.005.
• Suisun City Municipal Code, Allowable Uses in Residential Zones and use table — § 18.08.070 and Table 18.08.02.
• Suisun City Municipal Code — Definitions, including “legal nonconforming use” and yard provisions (see § 18.36.070).
• Suisun City Municipal Code — ADU rules and ministerial ADU approval provisions § 18.30.170.
• Suisun City Municipal Code — SB 9 urban lot split rules and ministerial correction of nonconforming conditions § 18.08.095 / SB 9 text.

Retrieved passages

• Suisun City Zoning Code (§ 3) High relevance show source text
• Suisun City Zoning Code (title shall) High relevance show source text
• Suisun City Zoning Code (§ 3) High relevance show source text
• Suisun City Zoning Code (§ 3) High relevance show source text
• CBC § 66321 (§ 66321) Medium relevance show source text
• Suisun City Zoning Code (§ 3) Medium relevance show source text
• Suisun City Zoning Code (title and) Medium relevance show source text
• Suisun City Zoning Code (Section 65583.2) Medium relevance show source text
• Suisun City Zoning Code (ARTICLE III.) Medium relevance show source text
• Suisun City Zoning Code (Section 11362.7) Medium relevance show source text
• Suisun City Zoning Code (§ 3) Medium relevance show source text
• Suisun City Zoning Code (section are) Medium relevance show source text
• CBC § 453.6.1 (Section 453.6.1_) Medium relevance show source text
• Suisun City Zoning Code (section 18.30.170) Medium relevance show source text
• Suisun City Zoning Code (§ 3) Medium relevance show source text
• Suisun City Zoning Code Medium relevance show source text

Cited sections

• Suisun City Municipal Code, Chapter 18.68, Nonconforming Uses — **§ 18.68.010** through **§ 18.68.070**. (Chapter 18.68)
• Suisun City Municipal Code, Chapter 18.31 and Table 18.31.01, Development Standards for Residential Zones (RL, RM, **RH1**, **RH2**, **RMU**) — **§ 18.31.005**. (Chapter 18.31)
• Suisun City Municipal Code, Allowable Uses in Residential Zones and use table — **§ 18.08.070** and Table 18.08.02. (§ 18.08.070)
• Suisun City Municipal Code — Definitions, including “legal nonconforming use” and yard provisions (see **§ 18.36.070**). (§ 18.36.070)
• Suisun City Municipal Code — ADU rules and ministerial ADU approval provisions **§ 18.30.170**. (§ 18.30.170)
• Suisun City Municipal Code — SB 9 urban lot split rules and ministerial correction of nonconforming conditions **§ 18.08.095 / SB 9 text**. (§ 18.08.095)
• SuisunCity_ZoningCode.md

• Official Suisun City code library