Local zoning · Tiburon

Tiburon — Nonconforming Uses

Q: What can I build on an R-1 lot in Tiburon?

You may build what the R-1 zone allows (primarily a single‑family dwelling and customary accessory uses) provided the project meets the R‑1 development standards (e.g., 10,000 s.f. min lot area , 30% lot coverage , 15 ft front setback, 8 ft side setbacks, 30 ft height) and any required permits; these numeric standards are in § 16-21.040 (Table 2‑2) .

Q: Can I add an addition to a nonconforming house that sits inside the setback?

Yes — but the addition cannot increase the discrepancy between the existing condition and the current standards, and the alteration generally requires Site Plan & Architectural Review approval; see the standards and process in § 16-62.030.B .

Q: If my nonconforming business closes for a year, can it reopen later?

No — if a legal nonconforming use is discontinued for a continuous period of one year , the nonconforming status is terminated and the site must thereafter conform to the current zone regulations; see § 16-62.030.A.3 .

Q: My building was 60% destroyed in a fire. Can I rebuild and resume the nonconforming use?

If more than 50% of the structural square footage used for the nonconforming use is involuntarily destroyed, the structure is considered destroyed and the nonconforming use cannot be resumed unless you first obtain a Conditional Use Permit and demonstrate General Plan consistency — see § 16-62.030.A.4.b . If ≤ 50% was destroyed, reconstruction may proceed provided work starts within one year and Site Plan/Architectural Review rules are followed.

Q: Do preexisting variances protect a nonconforming condition in Tiburon?

Yes. A structure is not considered nonconforming where the apparent nonconformity results solely from a Variance, Adjustment, or Conditional Use Permit that the Town (or formerly the County) granted and that subsequently vested; confirm the permit record with the Planning Department — see § 16-62.020 .

Q: If my commercial building in Downtown Tiburon is nonconforming, are there special rules?

Yes. Downtown properties and buildings inside the Historic Protection Overlay (HPO) must follow additional design standards (Downtown Tiburon Design Handbook) and HPO review requirements for exterior alterations; see § 16-23.060 and the commercial development standards in § 16-22.040 .

Q: Can an existing nonconforming accessory dwelling unit (ADU) be legalized in Tiburon?

The Code recognizes legal nonconforming secondary dwelling units and has local ADU rules (see § 16-52.100 ). However, the detailed interaction between State ADU statutes and local nonconforming conditions is not fully contained in the retrieved materials — verify with Planning and consult State ADU law. Not found in retrieved materials for the State/local crosswalk.

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

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Last reviewed: July 2, 2026

Overview

This page explains how the Town of Tiburon treats legal nonconforming uses, structures, and lots under the Town Zoning Ordinance (Title IV, Chapter 16). It summarizes the rules that control continuation, repair, alteration, destruction, abandonment, and redevelopment of nonconforming features, and then applies those rules to Tiburon’s actual zoning districts (so you can see what a nonconforming condition means in R-1, RO-1, R-2, NC, etc.). All requirements below are grounded in the Tiburon Zoning Ordinance; see the Source References for the controlling § citations.

Key rules that control nonconformities (plain statement)

The nonconforming rules are located in § 16-62.010–§ 16-62.040 (Purpose; Definitions; Restrictions on nonconforming structures/uses; Legal nonconforming lots). These are the controlling provisions for whether a pre‑existing use, building, or lot can continue, be altered, rebuilt, or must be brought into conformity.
A legal nonconforming use is a use lawfully established before the current Ordinance that no longer conforms to current use rules; a legal nonconforming structure is a lawfully erected building that no longer conforms to coverage, setback, height or similar standards. See § 16-62.020.
Nonconforming uses/structures may generally be continued and sold, and routine maintenance is allowed; but enlargement, intensification, or changing to another nonconforming use is prohibited. Discontinuance for a continuous period of one year terminates legal nonconforming status. § 16-62.030.
If a nonconforming structure is involuntarily damaged, the damage threshold matters: repair is allowed if ≤ 50% of the structural square footage used for the nonconforming use was destroyed and reconstruction starts within one year; if > 50% is destroyed, the nonconforming use cannot be resumed unless a Conditional Use Permit and General Plan consistency are demonstrated (§ 16-62.030[4]).
Nonconforming structures may be altered or enlarged only if the alteration does not increase the discrepancy with current standards and the project gets Site Plan & Architectural Review approval (§ 16-62.030[B]).
Legal nonconforming lots (lots that fail to meet current area/width/frontage) can be developed, but the applicant must show the lot was legally created or has a recorded certificate of compliance before a Zoning Permit for a vacant nonconforming lot is issued (§ 16-62.040).

Links you may need while using these rules: details on Tiburon’s parking, development standards (setbacks, coverage, FAR), design review (Site Plan & Architectural Review), overlay districts, ADUs, and the California Building Standards Code.

District-by-district breakdown (purpose, typical uses, key dimensional standards, where it applies)

Below are the Tiburon zoning districts most relevant to nonconforming issues. Each subsection shows 1) what the zone is for, 2) typical permitted uses, 3) the decision-relevant dimensional standards a nonconforming structure might contradict, and 4) where that zone is generally applied in town (from the Zoning Map and Section references).

Note: the Ordinance identifies the zone purposes in § 16-21.020 and the development standards (Table 2‑2 / Table 2‑3) in § 16-21.040 and § 16-22.040; overlays are in § 16-23. Use these to determine whether an existing building/use is nonconforming.

R-1 (Single-Family Residential)

Purpose: maintain suburban single‑family character. § 16-21.020 (A).
Typical permitted uses: single‑family dwellings, limited accessory uses; some home‑based day care uses; see Table 2‑1.
Key dimensional standards: Minimum lot area = 10,000 s.f., Maximum lot coverage = 30%, Front setback = 15 ft, Side setbacks = 8 ft, Primary height limit = 30 ft (Table 2‑2 / § 16-21.040). These are common bases for a legal nonconforming structure (e.g., pre‑existing smaller setback).
Where it applies: older suburban neighborhoods per the Zoning Map; see the zoning map and the Residential Zones section.

R-1-B / R-1-B-A / R-1-B-2 (Modified Single‑Family variants)

Purpose: annexed County lands with different historic setbacks; modified setbacks to avoid creating mass nonconformities. § 16-21.020 (B).
Typical uses: same as R-1 but with modified setbacks. See Table 2‑2 for the specific updated front/side setback dimensions.

RO-1 / RO-2 (Residential Open)

Purpose: low density/open residential (RO). § 16-21.020.
Typical uses: low‑density single family and open‑space compatible uses.
Key dimensional standards: RO-1 minimum lot area = 40,000 s.f., Maximum lot coverage = 15%, Front setback = 30 ft, Side setbacks = 20 ft (Table 2‑2 / § 16-21.040). A pre‑existing house that exceeds 15% coverage or sits inside the current setback becomes a legal nonconforming structure unless a variance was previously granted.

R-2 (Two‑Family Residential)

Purpose: allow two‑family dwelling patterns (Old Tiburon/Lyford’s Cove and other locations). § 16-21.020; R‑2 is common in Old Tiburon.
Typical uses: two‑family (mostly attached), secondary dwelling units where permitted, some multi‑unit forms subject to rules.
Key dimensional standards: Minimum lot area = 7,500 s.f., Maximum lot coverage = 35%, Front setback = 15 ft, Side setbacks = 8 ft (Table 2‑2 / § 16-21.040). Detached two‑family exceptions are discrete and, where historic detached two‑family dwellings existed, they may be treated as legal nonconforming structures (§ 16-40.020).

R-3, RPD, RMP (Multi‑Family and Planned Development)

Purpose: multifamily density and planned/multiple planned development managed under precise plan approvals. § 16-21.020 and RPD/RMP descriptions.
Typical uses: multi‑family dwellings, projects governed by Precise Development Plans; many changes require Conditional Use Permits or Precise Development Plan approvals.
Key standards: many RPD/RMP standards are set by precise plans rather than single numeric table entries; where not specified, Site Plan & Architectural Review determines appropriate setbacks/height. A pre‑existing building may be legal nonconforming if it predates the RPD/RMP standards.

NC (Neighborhood Commercial) and VC (Village Commercial / Downtown)

Purpose: neighborhood and downtown commercial activity; Downtown has special design guidance. § 16-22.010.
Typical uses: retail, restaurants, offices (with some restrictions in Downtown VC), and dwelling units above or behind storefronts in many places; many uses listed in Table 2‑3 (Commercial).
Key dimensional standards: NC minimum lot area = 10,000 s.f., Primary height = 30 ft (38 ft and up to 3 stories along Tiburon Blvd. for Downtown properties), and FAR limits in Table 2‑3. Downtown properties and the Historic Protection Overlay (HPO) have design and repair rules requiring consistency with the Downtown Tiburon Design Handbook. These numerical and design standards are common sources of nonconforming conditions.

Overlay Zones (Historic Protection, Flood Hazard, Affordable Housing Overlays)

Purpose: overlays add special rules — e.g., HPO (Historic Protection Overlay) requires retention of historic materials and extra review for exterior changes; F (Flood) restricts construction in special flood hazard areas. See § 16-23.050–16-23.060.
Effect on nonconformity: an alteration to a nonconforming structure inside an overlay may trigger more stringent review and additional submittal requirements (e.g., HPO: Director review and Downtown design consistency). Overlay rules can change whether a restoration is treated as a repair requiring only minor review versus full architectural review.

Most decision‑relevant standards (quick reference table)

Topic / Standard	Typical value (Tiburon)	When it matters	Code Reference
Termination for discontinuance	1 year continuous discontinuance → nonconforming use ends	Re‑establishment after vacancy/abandonment	§ 16-62.030 A.3
Destruction threshold for rebuild rules	50% of structural sq ft used for nonconforming use	If damage >50% → nonconforming use cannot resume without CUP & GP consistency	§ 16-62.030 A.4
R-1 minimum lot area	10,000 s.f.	Determines whether an existing house is nonconforming by lot area	§ 16-21.040 (Table 2‑2)
RO-1 lot coverage limit	15%	A pre‑existing building exceeding this becomes a nonconforming structure	§ 16-21.040 (Table 2‑2)
R-2 lot coverage	35%	Two‑family density and coverage conflicts	§ 16-21.040 (Table 2‑2)
Alterations to nonconforming structure	May be altered only if discrepancy is not increased; Site Plan & Architectural Review required	Any remodel, addition, or footprint change	§ 16-62.030 B
Legal nonconforming lots — proof required	Evidence of legal creation or recorded certificate of compliance before Zoning Permit for vacant lot	Developing a vacant nonconforming lot	§ 16-62.040 C

Checklist — what an applicant must satisfy (nonconforming repairs, rebuilds, or minor alterations)

Demonstrate the use/structure/lot was lawfully established (deed, prior permits, or certificate of compliance) — required for legal nonconforming lot status (§ 16-62.040).
Confirm whether the change is merely routine maintenance (allowed) or an alteration/enlargement (may be limited) under § 16-62.030.
If altering/remodeling, show the project will not increase the nonconformity and obtain Site Plan & Architectural Review documentation per § 16-62.030(B) and Tiburon Design Review procedures. See Tiburon design review.
For reconstruction after involuntary destruction: determine the percent of structural area destroyed (≤ 50% vs. > 50%) and follow the rebuild rules in § 16-62.030.A.4.
If the proposal would change the use (or increase intensity), confirm whether the new use would be a conforming use in the zone (Article II) or require a Conditional Use Permit (see Table 2‑1 and § 16-20.030).
If the lot is vacant and nonconforming, provide a certificate of compliance or legal creation record before the Town will issue a Zoning Permit (§ 16-62.040.C).

Risks & Ambiguities

Issue	Why it matters	What to verify
Abandonment / discontinuance (1‑year rule)	If a nonconforming use is discontinued for 1 year you lose legal nonconforming status and cannot reestablish it.	Verify continuous operation history (leases, utility bills, business licenses) to prove uninterrupted use. § 16-62.030.A.3
Destruction threshold (>50%)	If more than 50% of structural floor area used for the nonconforming use is involuntarily destroyed, resuming the use requires a CUP and GP consistency.	Confirm the method the Town will use to calculate % destroyed; obtain a structural/area assessment early. § 16-62.030.A.4
Previously‑granted variances / vested permits	A prior Variance, Adjustment, or Conditional Use Permit that vested means the condition is not treated as nonconforming. Missing records can create uncertainty.	Request Town permit records and review title/permit history to determine whether the existing condition is exempt from nonconforming rules. § 16-62.020
Alterations that “increase the discrepancy”	The Ordinance bars enlargements that worsen the nonconformity — this blocks many additions.	Verify existing dimension baseline(s) with survey and compare proposed change to confirm discrepancy is not increased. § 16-62.030.B.a
Nonconforming lots (legal creation proof)	Without proof the lot was legal when created, the Town may deny a permit for a vacant lot.	Produce recorded map, deed, or certificate of compliance before filing for a Zoning Permit. § 16-62.040.C
Interaction with overlays and Downtown design rules	Nonconforming commercial buildings in Downtown or HPO areas may require design compliance beyond numerical conformity.	Confirm overlay designation and follow Downtown Tiburon Design Handbook and HPO rules during review. § 16-23.060
ADUs and nonconforming zoning conditions	The Code defines a “legal nonconforming secondary dwelling unit” and references standards, but how ADU permitting intersects nonconformity is also influenced by State ADU law.	Check § 16-52.100 for local ADU standards and consult State ADU law; where the ordinance is silent on specific ADU/nonconforming interactions, verify with the Planning Department. § 16-52.100 — local reference; State rules not contained in retrieved materials.

Plain‑English Summary

If your house, business, or lot in Tiburon doesn’t meet today’s zoning rules but was legal when built, it’s probably a legal nonconforming use/structure/lot and can usually be kept and maintained — but you can’t make it more nonconforming, leave the use vacant for a year and then restart it, or rebuild after major destruction without extra approvals; specific thresholds and review steps are in § 16-62.010–§ 16-62.040.

Information Gaps

The Ordinance text in the materials defines legal nonconforming secondary dwelling unit and references local ADU rules (§ 16-52.100), but detailed cross‑walks between State ADU law and local nonconforming rules are Not found in retrieved materials. Verify ADU/nonconforming interactions with the Planning Division and the State ADU statutes.
Parcel‑specific determinations (e.g., percent destroyed calculations, historic variances, vested rights, or precise overlay boundaries on a parcel) are not determinable from this summary — Verify with the jurisdiction and request permit history and a pre‑application meeting.

Source References

Town of Tiburon Zoning Ordinance, § 16-62.010–16-62.040 (Nonconforming Uses, Structures, and Lots) — purpose, definitions, restrictions, legal nonconforming lots.
Tiburon Zoning Ordinance, § 16-62.020 (Definitions: Legal nonconforming use / structure).
Tiburon Zoning Ordinance, § 16-62.030 (Restrictions: maintenance, enlargement, discontinuance, destruction thresholds, alteration and review requirements).
Tiburon Zoning Ordinance, § 16-21.020 (Residential zone purposes) and § 16-21.040 (Table 2‑2 — Residential development standards: R‑1, RO‑1, R‑2, etc.).
Tiburon Zoning Ordinance, § 16-22.040 and Table 2‑3 (Commercial zone development standards: NC, VC, FAR and height limits).
Tiburon Zoning Ordinance, § 16-23.050–16-23.060 (Overlay Zones; Historic Protection Overlay rules and Downtown design guidance).
Definitions and cross‑references (Article X; ADU / secondary dwelling definitions; Site Plan & Architectural Review references) — see Article X and § 16-52.020 / § 16-52.100 for ADU rules.

Sources

Retrieved passages

Tiburon Zoning Code (Article VI) High relevance
Tiburon Zoning Code (Chapter 16A) High relevance
CFC § 16 (Article VI) High relevance
CFC § 2010 (Article VI) High relevance
Tiburon Zoning Code (Chapter 14) High relevance
Tiburon Zoning Code (Article VI) High relevance
Tiburon Zoning Code (Chapter 14) High relevance
Tiburon Zoning Code (Section shall) High relevance
Tiburon Zoning Code (Article IV) Medium relevance
Tiburon Zoning Code (Section 16-52.040) Medium relevance
CBC § 66321 (§ 66321) Medium relevance
Tiburon Zoning Code (Section 16-21.040) Medium relevance
Tiburon Zoning Code (Article II) Medium relevance
Tiburon Zoning Code (Section 16-40.020.) Medium relevance
Tiburon Zoning Code (TITLE BLOCK) Medium relevance
Tiburon Zoning Code (Title IV) Medium relevance

Cited sections

Official Tiburon code library

Frequently asked questions

What can I build on an R-1 lot in Tiburon?

You may build what the R-1 zone allows (primarily a single‑family dwelling and customary accessory uses) provided the project meets the R‑1 development standards (e.g., 10,000 s.f. min lot area, 30% lot coverage, 15 ft front setback, 8 ft side setbacks, 30 ft height) and any required permits; these numeric standards are in § 16-21.040 (Table 2‑2).

What makes a building a "legal nonconforming structure" in Tiburon?

A structure is legal nonconforming if it was lawfully built under earlier rules but now violates current standards for lot coverage, setbacks, height, distance between structures, or similar requirements; see the definition in § 16-62.020.

Can I add an addition to a nonconforming house that sits inside the setback?

Yes — but the addition cannot increase the discrepancy between the existing condition and the current standards, and the alteration generally requires Site Plan & Architectural Review approval; see the standards and process in § 16-62.030.B.

If my nonconforming business closes for a year, can it reopen later?

No — if a legal nonconforming use is discontinued for a continuous period of one year, the nonconforming status is terminated and the site must thereafter conform to the current zone regulations; see § 16-62.030.A.3.

My building was 60% destroyed in a fire. Can I rebuild and resume the nonconforming use?

If more than 50% of the structural square footage used for the nonconforming use is involuntarily destroyed, the structure is considered destroyed and the nonconforming use cannot be resumed unless you first obtain a Conditional Use Permit and demonstrate General Plan consistency — see § 16-62.030.A.4.b. If ≤ 50% was destroyed, reconstruction may proceed provided work starts within one year and Site Plan/Architectural Review rules are followed.

Do preexisting variances protect a nonconforming condition in Tiburon?

Yes. A structure is not considered nonconforming where the apparent nonconformity results solely from a Variance, Adjustment, or Conditional Use Permit that the Town (or formerly the County) granted and that subsequently vested; confirm the permit record with the Planning Department — see § 16-62.020.

How does a legal nonconforming lot get developed in Tiburon?

Legal nonconforming lots may be developed, but before issuing a Zoning Permit for a vacant nonconforming lot the Town requires evidence that the lot was legally created or a recorded certificate of compliance consistent with the State Subdivision Map Act — see § 16-62.040.C.

If my commercial building in Downtown Tiburon is nonconforming, are there special rules?

Yes. Downtown properties and buildings inside the Historic Protection Overlay (HPO) must follow additional design standards (Downtown Tiburon Design Handbook) and HPO review requirements for exterior alterations; see § 16-23.060 and the commercial development standards in § 16-22.040.

Can an existing nonconforming accessory dwelling unit (ADU) be legalized in Tiburon?

The Code recognizes legal nonconforming secondary dwelling units and has local ADU rules (see § 16-52.100). However, the detailed interaction between State ADU statutes and local nonconforming conditions is not fully contained in the retrieved materials — verify with Planning and consult State ADU law. Not found in retrieved materials for the State/local crosswalk.

Who makes the final decision if I disagree with the Planning Director’s interpretation about a nonconforming status?

Appeals and review authorities are described in Article VI; appeals of Zoning Permit decisions and interpretations follow the appeals process in § 16-66 and the administrative responsibilities in § 16-60. Verify the applicable review authority for your specific permit.

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