Local zoning · Marin County

Marin County — Nonconforming Uses

Nonconforming Uses under the Marin County local zoning and planning code, with the controlling citations.

Last reviewed: July 6, 2026

Overview

This page explains how Marin County regulates legal nonconforming uses, structures, and lots in unincorporated areas, with a focus on the County’s certified Local Coastal Program (LCP) rules that apply inside the Coastal Zone. The controlling provisions for the Coastal Zone are in the Coastal Zoning Code, including definitions in § 20.130 and the core standards for nonconformities in § 20.70.160 . Inland (non‑coastal) areas are governed by the Marin County Development Code (Title 22), which is separate from the Coastal Zoning Code; inland nonconforming standards were not included in the retrieved materials (see Information Gaps). For background on how these rules fit into Marin’s broader zoning and land use framework, start with the County’s zoning & planning overview.

Most important rule in plain English: a legal nonconforming use may continue but cannot be expanded or intensified, and if it stops for 12 consecutive months it loses its protected status; for structures, replacing 50% or more (cumulative) turns the project into a new, conforming structure (§ 20.70.160.C–E) .

What counts as a nonconformity in the Coastal Zone

Definitions. The LCP defines a Nonconforming Use, Nonconforming Structure, and Nonconforming Lot in § 20.130 (Coastal Zoning Code Definitions) . A nonconforming lot is a legally created “lot of record” that no longer meets current standards; a nonconforming use or structure was legally established but no longer conforms due to later standards.
Burden of proof. The property owner must prove the legal nonconforming status to the satisfaction of the Director (§ 20.70.160.B) .
Nonconforming uses — limits. They cannot be expanded or intensified; “intensification” for non‑residential uses includes changes likely to increase traffic, noise, smoke, glare, odors, hazardous materials, water use, and/or sewage generation as determined by the Director (§ 20.70.160.C) .
Abandonment. If a nonconforming use stops for 12 months or longer, the nonconforming status is lost; any subsequent use must conform to current LCP regulations (§ 20.70.160.C) .
Nonconforming structures — 50% rule. Repairs and maintenance are allowed, but replacing 50% or more of a nonconforming structure is not “repair/maintenance” and requires bringing the structure into full conformance. The 50% calculation is cumulative (§ 20.70.160.D–E) .
Blufftop/shoreline sites. The same 50% rule applies; replacement 50%+ must fully conform to LCP policies (§ 20.70.160.F) .
Natural disaster. If destroyed by natural disaster, replacement is subject to the Coastal Zoning Code’s exemptions and CDP rules (see § 20.68.050.C, referenced by § 20.70.160.G) .
Legal lots only. “Development may only be undertaken on a legal lot” (§ 20.70.175.C) .

Marin’s Coastal Zone rules operate alongside countywide processes like design review and development standards. Also note that certain topics (e.g., parking, landscaping and screening, signage) can still apply to projects that touch nonconforming sites or structures.

Coastal Zone: how districts frame what “conforming” means

In the Coastal Zone, each zoning district’s allowed uses and LCP standards define what is conforming. Allowed uses are organized in § 20.62.040 and its tables (Agricultural/Resource, Residential, and Commercial/Mixed‑Use) . Below is a district‑by‑district snapshot to help you identify the baseline to which a nonconforming use or structure would need to align if it’s ever changed enough to trigger full compliance.

C-APZ — Agricultural Production Zone

Purpose: Agricultural production (implied by district name). Formal purpose statement: Not found in retrieved materials.
Typical permitted uses: Agricultural production and related activities; certain dwellings in agricultural contexts; single‑family dwellings are principally permitted in C‑APZ per the tables (see § 20.62.040 tables) .
Key dimensional standards: Not found in retrieved materials; development must meet LCP standards referenced throughout § 20.62.040 and Chapters 20.64–20.66 (see cross‑references in tables) .
Notes for nonconforming uses: No expansion/intensification; 12‑month abandonment rule; 50% cumulative replacement for structures (§ 20.70.160.B–F) .

C-ARP — Agricultural Residential Planned

Typical permitted uses: Agricultural and residential uses; accessory agricultural structures; some residential care and home occupations as permitted in the tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-OA — Open Area

Typical permitted uses: Limited residential/agricultural activities; many uses require a Use Permit as shown in tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-RA — Residential Agricultural

Typical permitted uses: Single‑family dwellings (PP), ADUs (PP), guest houses (P), and agricultural accessory structures (P) per tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-R1 — Single Family

Typical permitted uses: Single‑family dwellings (PP), ADUs (PP), group homes (P/U) per tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-R2 — Two Family

Typical permitted uses: Two‑family dwellings (PP), single‑family (PP), ADUs (PP) per tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-RSPS — Single Family Seadrift Subdivision

Where it applies: Seadrift Subdivision in the Coastal Zone (as named).
Typical permitted uses: Single‑family dwellings (PP) and ADUs (PP) per tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160, F applies for shoreline/blufftop) .

C-RSP — Single Family Planned

Typical permitted uses: Single‑family dwellings (PP), ADUs (PP), certain agricultural accessory uses (P) per tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-RMP — Multiple Planned

Typical permitted uses: Multi‑family dwellings (PP) and residential accessory uses (PP); ADUs (PP) per tables (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-VCR — Village Commercial Residential

Typical permitted uses: A mix of agricultural, small‑scale commercial, and reverse‑vending recycling; “village commercial/residential” mix per the table (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-H1 — Limited Roadside Business

Typical permitted uses: Limited roadside commercial uses; some uses require Use Permits as noted in the table (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-CP — Planned Commercial

Typical permitted uses: Planned commercial and certain agricultural/commercial uses per table (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-RMPC — Residential Commercial Multiple Planned

Typical permitted uses: Mixed residential/commercial program per table (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above (§ 20.70.160) .

C-RCR — Resort and Commercial Recreation

Typical permitted uses: Resort/commercial recreation and supporting activities per table (§ 20.62.040 tables) .
Dimensional standards: Not found in retrieved materials.
Nonconforming use rules: As above; shoreline rules are especially relevant (§ 20.70.160.F) .

Decision‑relevant rules (Coastal Zone)

Topic	What the LCP says	Applies where	Code Reference
Proof of nonconforming status	Owner bears burden to prove legal status to Director	All Coastal districts	§ 20.70.160.B
Expand/intensify a nonconforming use?	Not allowed; “intensification” includes traffic, noise, smoke, glare, odors, hazmat, water/sewage impacts	All Coastal districts	§ 20.70.160.C
Abandonment	12+ months of discontinuance = status lost	All Coastal districts	§ 20.70.160.C
Maintenance/repair of nonconforming structures	Allowed if under 50% replacement; cumulative over time	All Coastal districts	§ 20.70.160.D–E
Replace ≥50% of a nonconforming structure	Treated as a replacement structure; must fully conform to LCP	All Coastal districts	§ 20.70.160.D–E
Blufftop/shoreline structures	Same 50% rule; replacement must conform	Blufftop/shoreline sites	§ 20.70.160.F
After natural disaster	Replacement subject to Coastal Zoning Code CDP/exemption provisions	All Coastal districts	§ 20.70.160.G (ref. § 20.68.050.C)
Must be a legal lot	Development may only occur on a legal lot	All Coastal districts	§ 20.70.175.C
Variance as a “fix”	Variances can’t waive use limits or minimum lot size/density	All Coastal districts	§ 20.70.150.B.2

Practical tie‑ins:

Allowed uses by district are outlined in § 20.62.040 and its tables; use these to understand what a future “conforming” use would be if a nonconforming use terminates or a structure crosses the 50% threshold .
Design changes that move a project into “replacement structure” territory generally must meet all current Coastal LCP development standards and may require design review, separate from any Coastal Development Permit (noted in the tables) .
State ADU law limits a local agency’s ability to deny an ADU due to existing nonconforming zoning conditions if they are not health/safety threats; this can matter if you’re adding an ADU to a site with older setbacks or parking layouts (see HCD’s 2025 ADU Handbook) . For state rules, see California ADU law.

Checklist

Confirm the site is in unincorporated Marin County and whether it lies in the Coastal Zone or inland area (overlay districts can change which code applies).
Identify the current zoning district and allowed uses in § 20.62.040 tables (Agricultural/Resource, Residential, Commercial/Mixed‑Use) .
Gather evidence that the use/structure/lot was lawful when established (title, permits, assessor records); submit to the Director to establish legal status (§ 20.70.160.B) .
If the use stopped, document whether any gap approached or exceeded 12 months (§ 20.70.160.C) .
Scope all work on a nonconforming structure; track cumulatively whether replacement equals/exceeds 50% (§ 20.70.160.D–E) .
For blufftop or shoreline properties, flag the stricter replacement trigger (§ 20.70.160.F) .
Verify the parcel is a legal lot if any development is proposed (§ 20.70.175.C) .
If seeking relief from setbacks, height, or FAR, evaluate a variance; do not rely on a variance to legalize a prohibited use or substandard lot size (§ 20.70.150.B.2) .
Coordinate required Coastal permits with any County design approvals; design review is separate and in addition to CDP (noted in tables) .

Risks & Ambiguities

Issue	Why it matters	What to verify
Proving “legal” status	Without proof, protections for nonconforming status don’t apply	Evidence acceptable to the Director (§ 20.70.160.B)
What is “intensification”?	Certain changes to a nonconforming use may be denied	Whether proposed changes increase traffic/noise/etc. per Director (§ 20.70.160.C)
50% replacement is cumulative	Phased work can unintentionally trigger full conformance	County’s tracking methodology and baseline; cumulative per § 20.70.160.D–E
Coastal bluff/shoreline sites	Stricter treatment for replacements near sensitive edges	Whether site is blufftop/shoreline; conformance per § 20.70.160.F
Legal lot status	Development only allowed on legal lots	Parcel’s legal status and any needed lot adjustments (§ 20.70.175.C)
Using a variance to “fix” a use	Variances can’t authorize prohibited uses/lot sizes	Relief is limited to height/FAR/setbacks (§ 20.70.150.B.2)
ADUs on nonconforming sites	State law limits denial for nonconforming conditions	Whether the condition is a health/safety risk; see HCD ADU guidance
Historic structures	Special review can affect alterations	Whether the building qualifies as a “Historic Structure” in definitions; see historic preservation and definitions in § 20.130

Plain-English Summary

In unincorporated coastal Marin, you can keep using a legally built but now‑nonconforming building or use, but you can’t make the use bigger or more intense, and stopping it for a year ends that protection. You can repair an older nonconforming building, but once you replace half or more (counted over time), the whole thing must meet today’s rules. On the coast—especially near bluffs or the shoreline—replacement projects trigger full compliance even faster.

Source References

Marin County Coastal Zoning Code — Nonconforming Uses and Structures: § 20.70.160
Marin County Coastal Zoning Code — Coastal Zone Variances: § 20.70.150.B.2
Marin County Coastal Zoning Code — Enforcement; development on legal lots: § 20.70.175.C
Marin County Coastal Zoning Code — Allowed Uses framework: § 20.62.040 and district tables (Tables 5‑1, 5‑2, 5‑3)
Coastal Zoning Code Definitions — Nonconforming Use/Structure/Lot: § 20.130 (Definitions)
State ADU context — 2025 HCD ADU Handbook (re: nonconforming zoning conditions)
Related County topics: Development Standards, Design Review, Parking, Overlay Districts, Historic Preservation, California Building Standards Code, California ADU law

Information Gaps

Inland (non‑Coastal) Marin Development Code provisions for nonconforming uses/structures/lots (Title 22): Not found in retrieved materials.
Numeric dimensional standards (e.g., setbacks, height) by Coastal district: Not found in retrieved materials. Verify with the jurisdiction.

Sources

Retrieved passages

Marin County Zoning Code (Section A) High relevance
Marin County Zoning Code (section shall) High relevance
Marin County Zoning Code (Section 20.70.050) High relevance
Marin County Zoning Code (Chapter 20.130) Medium relevance
Marin County Zoning Code (Section 15369.5) Medium relevance
Marin County Zoning Code (Section 4511) Medium relevance
Marin County Zoning Code (§ 66314) Medium relevance
Marin County Zoning Code (Chapter 22.22) Medium relevance
Marin County Zoning Code (Chapter 22.48) Medium relevance
Marin County Zoning Code (§ 66333) Medium relevance
Marin County Zoning Code (Chapter 20.130) Medium relevance

Cited sections

Official Marin County code library

Frequently asked questions

Can I expand a legal nonconforming restaurant in unincorporated coastal Marin?

No. Nonconforming uses may continue but cannot be expanded or intensified; “intensification” includes increases in traffic, noise, smoke, glare, odors, hazardous materials, water use, or sewage generation as determined by the Director (§ 20.70.160.C) .

If I stop operating my nonconforming use for a year, can I restart it later?

Not as a nonconforming use. If the use is abandoned for a continuous 12 months or more, it loses its legal nonconforming status; any new use must conform to current LCP regulations (§ 20.70.160.C) .

What is the “50% rule” for nonconforming coastal structures?

You can repair and maintain a legal nonconforming structure, but once 50% or more is replaced (cumulative over time), the project becomes a replacement structure that must fully conform to the LCP (§ 20.70.160.D–E) .

Do special rules apply to blufftop or shoreline houses that are nonconforming?

Yes. For legal nonconforming structures on blufftops or along the shoreline, replacing 50% or more is treated as a replacement structure that must conform to LCP policies and standards (§ 20.70.160.F) .

Can a variance make my nonconforming use “legal” or fix a substandard lot size?

No. Variances may only address height, FAR, and setbacks; they cannot authorize prohibited uses or waive minimum lot size or density requirements (§ 20.70.150.B.2) .

Can I develop if my parcel is a nonconforming lot?

Development may only proceed on a legal lot (§ 20.70.175.C) . A “nonconforming lot” is defined in § 20.130, but additional allowances/limitations beyond being a legal lot were not found in the retrieved materials; verify with the jurisdiction .

How do I figure out what the “conforming” use would be in my coastal zoning district?

Check the allowed‑use tables for your district in § 20.62.040 (Tables 5‑1, 5‑2, 5‑3). These show principal/permitted/conditional uses by district and frame what future conforming use(s) would be if a nonconforming use terminates .

Can I add an ADU if my property has nonconforming setbacks or parking?

Often yes. State ADU law limits denial of ADUs due to existing nonconforming zoning conditions unless they present a health/safety risk affected by the ADU work; see HCD’s 2025 ADU Handbook and California ADU law for details .

Does rebuilding after wildfire change the nonconforming status?

If a legal nonconforming structure is destroyed by natural disaster, replacement is processed under the Coastal Zoning Code’s CDP/exemption framework referenced by § 20.70.160.G; coordinate early to confirm whether a Coastal Development Permit or exemption applies .

Do design review and current standards apply when I alter a nonconforming structure?

Yes. Design review applies independently of Coastal permits as noted in the use tables, and any new work must meet today’s standards unless specifically preserved under nonconforming rules; verify triggers through design review and development standards references in § 20.62.040 tables .

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