Local zoning · Diamond Bar

Diamond Bar — Nonconforming Uses

Q: What happens if a nonconforming use stops operating?

If the nonconforming use is discontinued for 180 continuous days , the nonconforming status is lost and future use must comply with current district rules. The director will evaluate evidence of ongoing use when in doubt. See § 22.68.050(a) .

Q: My building was damaged — can I rebuild a nonconforming structure?

If repair/replacement costs are ≤50% of appraised/replacement value and reconstruction begins within one year, the structure may be restored and the nonconforming use continued. If costs exceed 50% , a Minor CUP is required to restore and continue the use. See § 22.68.050(b) .

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

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Last reviewed: July 2, 2026

Overview

This page explains how the City of Diamond Bar regulates nonconforming uses, nonconforming structures, and nonconforming parcels under the Title 22 — Development Code. The municipal rules are in Chapter 22.68 (purpose, continuation, alteration, abandonment, reconstruction) and tie into the city’s district development standards and permit procedures; see § 22.68.010 and related provisions for the controlling policy and intent.

Before you act on a nonconformity verify zoning, development standards, and whether a land use is still lawful under Title 22; the Development Code’s applicability rules are in § 22.01.040.

What the Code actually says (key rules)

Continuation: A legal nonconforming use may be continued, transferred, and sold but generally may not be enlarged or intensified beyond what existed when it became nonconforming. See § 22.68.020.
Expansion limits in conforming structures: A nonconforming use occupying part of a conforming structure may expand within that structure one time only and by no more than 10% of total floor area before expansion. See § 22.68.020(b)(1).
Nonconforming structure changes: Additions, enlargements, reconstruction, relocation or structural alteration of a nonconforming structure require a minor conditional use permit unless the work fits specified exceptions (residential first-floor additions can match existing adjoining setbacks under limits). See § 22.68.030 and the Minor CUP rules in § 22.56.020–040.
Repairs & thresholds: Routine maintenance is allowed; “minor” work is permitted without discretionary approval provided structural alteration does not exceed 25% of appraised/replacement value in a one-year period. Work above that threshold generally requires hearing officer approval under the Minor CUP procedure; major repairs are treated differently if damage exceeds 50% of appraised/replacement value. See § 22.68.030(e) and § 22.68.050(b).
Abandonment: If a nonconforming use is discontinued for 180 days (continuous), the right to continue the nonconforming use terminates. The director may require evidence of continuous operation when evaluating abandonment. See § 22.68.050(a).
Destruction: If a nonconforming structure is damaged, it may be rebuilt without a Minor CUP only when the cost to repair does not exceed 50% of the appraised/replacement value and reconstruction begins within one year of damage; otherwise a Minor CUP is required. See § 22.68.050(b).
Nonconforming parcels: A parcel that fails to meet current access, width or area standards may still be a legal building site if it was legally created before the amendment, was part of an approved subdivision, resulted from an approved variance/lot-line adjustment, or was reduced by government acquisition not exceeding specified percentages. See § 22.68.060.
Parking nonconformity: If a structure is nonconforming only because of deficient off‑street parking, limited changes are allowed without CUPs; residential changes typically will not trigger additional parking unless they increase dwelling units. See § 22.68.030(d).

Reference table (quick decision guide)

Rule	What it means for your project	Code Reference
Continue existing use but no enlargement	You may run/sell/transfer the use but cannot expand the area or intensity beyond pre-existing extent	§ 22.68.020
Single in‑structure expansion cap	One expansion only, max 10% of structure floor area (conforming structure w/ nonconforming use)	§ 22.68.020(b)(1)
Repairs — minor vs. major	≤ 25% of appraised/replacement value = minor; > 50% = major (triggers different approvals)	§ 22.68.030(e) and § 22.68.050(b)
Abandonment	Continuous discontinuance ≥180 days = nonconforming rights terminate	§ 22.68.050(a)
Rebuild after >50% loss	Rebuild needs a Minor CUP unless special exception applies	§ 22.68.050(b)(2)
Nonconforming parcel acceptance	Parcel OK if legally created by deed/subdivision, variance, lot-line adjustment, or small gov’t acquisition	§ 22.68.060

District-by-district breakdown (how nonconforming rules interact with each district)

Note: the Development Code establishes zoning districts and specific development standards by Table; the district rules below summarize the usual development standard references and where nonconforming rules interact with each. Always verify a parcel’s actual zoning on the official map and confirm parcel-specific constraints. See § 22.06.040 for how district standards are applied.

Residential districts — RR, RL, RLM, RM, RMH, RH, RH-30

Purpose: These districts range from rural single-family to high-density multifamily; residential development standards are in Table 2-4 and the Residential District general standards. See § 22.08.040.
Typical permitted uses: Single‑family dwellings, multifamily as allowed in higher-density districts, accessory uses (garages, ADUs), neighborhood services where listed in the use tables. See Article II tables.
Key dimensional standards (examples from Table 2‑4): minimum lot areas and densities vary (e.g., RR often 1 acre minimum; RL ~10,000 sq.ft; RLM/ RM higher densities; RH-30 targets up to 30 du/net acre). See Table 2‑4 and § 22.08.040.
Where it applies: City residential neighborhoods; nonconforming setbacks or lot coverage are treated under § 22.68.030 for structures — small first‑floor additions may match adjacent setbacks within limits (no need for Minor CUP if they meet criteria).

Practical note: ADUs created under § 22.42.120 may not be denied solely because of unrelated nonconforming zoning conditions in many cases; consult the ADU rules. Link to the local ADU page for process specifics: Diamond Bar ADUs.

Commercial districts — C-1, C-2, C-3

Purpose: Serve local, neighborhood and general commercial needs; development standards are in Table 2‑7 and § 22.10.040.
Typical permitted uses: Retail, restaurants, offices, service uses per the district use tables (Tables 2‑5/2‑6). Uses that were lawful before a rezone but now prohibited may be nonconforming uses and continue under § 22.68.020.
Key dimensional standards: typical front landscape setback = 10 ft, side/rear setbacks of 10 ft when abutting residential, FAR ranges 0.25–1.0, height limits often 35 ft in commercial zones (see Table 2‑7).
Where it applies: Shopping centers, neighborhood commercial strips. Nonconforming parking deficiencies are specifically addressed; see § 22.68.030(d) (nonresidential parking) and the local [parking] page for calculation details.

Industrial / Institutional — I and related districts

Purpose & uses: Industrial/manufacturing/service uses listed in Table 2‑7; subject to the same nonconforming structure and use rules in Chapter 22.68.
Key development standards: larger minimum lot sizes (e.g., 20,000 sq.ft. for some industrial), height and FAR rules in Table 2‑7. Changes to nonconforming industrial structures (e.g., expansions, reconstructing after damage) follow § 22.68.030 and Minor CUP procedures for structural alterations.

Special purpose and overlay districts — H (Housing Element site) and others

Purpose: Overlay districts modify allowed uses and standards on specific parcels. The (H) overlay allows multifamily dwellings on specified housing element sites, and uses RH‑30 standards where applicable. See § 22.14.050.
Interaction with nonconforming rules: Where overlays change permitted uses, an existing use prohibited by the overlay may become nonconforming and be governed by Chapter 22.68; verify whether the site was designated in a specific plan or is subject to special standards. See § 22.68.010 and overlay rules.

How to proceed (Checklist)

Confirm the property’s current zoning district on the official map and identify the applicable district code (e.g., R-1, C-1, RH-30) and underlying Table (Table 2‑4 / 2‑7). See § 22.06.040 and Table references.
Establish whether the existing use or structure was lawfully established under prior rules (legal nonconforming) — gather deeds, permits, photos, business records. See § 22.68.010 and § 22.68.060 for parcel proof standards.
Determine if proposed work is maintenance, minor repair (≤ 25% of appraised/replacement value in 12 months), major repair (> 50%) or expansion; pick the correct approval path. See § 22.68.030(e) and § 22.68.050(b).
If expansion or structural alteration is needed, prepare a Minor Conditional Use Permit (Minor CUP) application in compliance with § 22.56.020–040 (including findings).
If parking deficiency is the only nonconformity, assemble parking calculations and, if changing use, a parking study may be required as prescribed in § 22.68.030(d). Link to Diamond Bar Parking for local rules.
If the nonconforming use has been inactive, provide records proving continuous operation (to avoid the 180‑day abandonment presumption). See § 22.68.050(a).
If the structure was damaged, calculate repair cost vs. appraised/replacement value to see if rebuilding triggers Minor CUP. See § 22.68.050(b).
Coordinate any required design review, sign, landscaping, or parking approvals (see the Development Standards, Design Review, and Signage pages). Link to Diamond Bar Design Review and Diamond Bar Development Standards.

Risks & Ambiguities

Issue	Why it matters	What to verify
Is the use truly “legal nonconforming”?	Illegal uses are not protected; Chapter 22.68 only protects legally established nonconformities. See § 22.68.010 and § 22.68.090.	Verify historic permits, plats, deeds, or evidence of lawful establishment; ask the director if documentation is unclear.
Abandonment after inactivity	Continuous inactivity ≥180 days terminates rights; the director’s discretion on “continuous” is administrative. See § 22.68.050(a).	Produce rent rolls, receipts, utility records, or business filings to prove continuity.
Repair cost thresholds	Whether work is “minor” (≤ 25%) or “major” (> 50%) changes required approvals and outcome. See § 22.68.030(e) and § 22.68.050(b).	Obtain appraised/replacement value from county assessor and a contractor estimate; confirm threshold math with staff.
Parking shortfall vs. new use	Changing a use with greater parking demand can force additional parking or a parking study; nonresidential underparking by 25%+ may require a study. See § 22.68.030(d).	Verify required parking for the proposed use (Chapter 22.30) and whether the proposed change increases parking needs.
Parcel legality	A nonconforming parcel may still be a legal building site only if specific historic criteria are met. See § 22.68.060.	Confirm recorded deed/subdivision, lot-line history, or variance approvals; verify against Subdivision Map Act compliance.

Plain-English Summary

Diamond Bar allows lawful nonconforming uses and structures to remain in operation but restricts enlargement, requires discretionary review for many structural changes, and ends nonconforming rights after long inactivity or major destruction; read Chapter 22.68 to see the exact thresholds (180 days abandonment, 25%/50% repair thresholds, 10% in‑structure expansion limit).

Source References

Title 22 — Diamond Bar Development Code, Chapter 22.68 (Nonconforming Uses, Structures, and Parcels): § 22.68.010 (Purpose) through § 22.68.090 (Unlawful uses).
§ 22.68.020 (Restrictions on nonconforming uses).
§ 22.68.030 (Restrictions on nonconforming structures — building envelope, Minor CUP, maintenance/repair thresholds).
§ 22.68.050 (Loss of nonconforming status — abandonment/destruction rules).
§ 22.68.060 (Nonconforming parcels — criteria for legal building site).
Minor conditional use permit rules: § 22.56.020–040 (applicability, findings, process).
Residential district standards and Table 2‑4: § 22.08.040 (Residential district general development standards).
Commercial/Industrial district standards and Table 2‑7: § 22.10.040.
Zoning district framework: § 22.06.040 (Zoning district regulations and tables).
ADU local rules: § 22.42.120 (Accessory dwelling units and JADUs).

Also consult the local pages for process or standards referenced above (use the city pages on zoning, development standards, parking, design review, overlays, ADUs, and the California Building Standards Code):

Diamond Bar zoning & planning overview (/us/california/diamond-bar) — for map/contacts.
Diamond Bar Zoning (/us/california/diamond-bar/zoning) — zoning district map and tables.
Diamond Bar Development Standards (/us/california/diamond-bar/development-standards) — setbacks, height, lot coverage.
Diamond Bar Parking (/us/california/diamond-bar/parking) — off-street parking rules invoked by § 22.68.030(d).
Diamond Bar Design Review (/us/california/diamond-bar/design-review) — when design review applies.
Diamond Bar Overlay Districts (/us/california/diamond-bar/overlay-districts) — overlays (including (H) overlay) interact with nonconforming rights.
Diamond Bar ADUs (/us/california/diamond-bar/adu) — ADU-specific references and state ADU constraints.
California Building Standards Code (/us/california/building-codes) — for seismic/Title 24 compliance exceptions referenced in § 22.68.030(f).

Sources

Retrieved passages

Diamond Bar Zoning Code (§ 2) High relevance
Diamond Bar Zoning Code (§ 2) High relevance
Diamond Bar Zoning Code (section creates) High relevance
Diamond Bar Zoning Code (chapter 22.54) High relevance
Diamond Bar Zoning Code (chapter 22.56) High relevance
Diamond Bar Zoning Code (chapter 22.56) High relevance
CBC § 22.68.030 (section 22.68.030) High relevance
CFC § 2 (chapter 22.56) High relevance
Diamond Bar Zoning Code (title 7) Medium relevance
Diamond Bar Zoning Code (section 22.04.020) Medium relevance
CBC § 66321 (§ 66321) Medium relevance
CBC § 2 (§ 2) Medium relevance
CBC § 2 (§ 2) Medium relevance
Diamond Bar Zoning Code (section 22.16.090) Medium relevance
CFC § 2 (Title 22) Medium relevance

Cited sections

Official Diamond Bar code library

Frequently asked questions

What is a nonconforming use in Diamond Bar?

A nonconforming use in Diamond Bar is a land use or structure that was legally established under earlier rules but would not be allowed (or would be restricted differently) under the current Development Code. The Development Code’s purpose and general approach are in § 22.68.010; specific continuation and restriction rules are in § 22.68.020.

Can I expand a business that is a nonconforming use?

Maybe — a nonconforming use of land or of a conforming structure may be continued but generally may not be enlarged or intensified. An exception allows expansion within a conforming structure one time up to 10% of floor area if other criteria are met; see § 22.68.020(b)(1).

If my house has nonconforming setbacks can I add an addition?

Small first‑floor or lower‑level additions can be allowed to match an existing adjoining portion’s side setbacks under limited conditions; otherwise changes to nonconforming structures generally require a Minor Conditional Use Permit. See § 22.68.030(b) and the Minor CUP procedures § 22.56.020–040.

What happens if a nonconforming use stops operating?

If the nonconforming use is discontinued for 180 continuous days, the nonconforming status is lost and future use must comply with current district rules. The director will evaluate evidence of ongoing use when in doubt. See § 22.68.050(a).

My building was damaged — can I rebuild a nonconforming structure?

If repair/replacement costs are ≤50% of appraised/replacement value and reconstruction begins within one year, the structure may be restored and the nonconforming use continued. If costs exceed 50%, a Minor CUP is required to restore and continue the use. See § 22.68.050(b).

Is a nonconforming parcel a legal building site?

A parcel that does not meet current area, width, or access rules may still be a legal building site if it was legally created by recorded deed or approved subdivision before the amendment, resulted from an approved variance/lot-line adjustment, or met other narrow criteria listed in § 22.68.060. Verify parcel history with the city; see § 22.68.060.

Does a parking deficiency make my building nonconforming and stop me from changing uses?

A parking deficiency can render a structure nonconforming, but the code allows changes under § 22.68.030(d): residential uses generally won't be required to add parking unless the change increases dwelling units; nonresidential uses may occupy the structure if the new use has equal or fewer parking needs, or a parking study supports change where underparking is 25%+.

If an overlay changed allowable uses, can my pre‑existing use remain?

Yes. A use that was lawful before an overlay or map amendment can be treated as a nonconforming use and continued in the limited manner described in Chapter 22.68. Confirm overlay specifics (for example, the (H) overlay) in § 22.14.050.

Do ADU rules affect nonconforming zoning conditions on my lot?

Diamond Bar’s ADU rules reference state law and allow ADU ministerial processing in many cases; state ADU law and local § 22.42.120 restrict denial of ADUs solely because of certain nonconforming zoning conditions. See § 22.42.120 for local ADU interpretation and the ADU page for process.

When will I need a Minor Conditional Use Permit for nonconforming changes?

You will need a Minor CUP for most structural additions, enlargements, relocations, or other alterations to nonconforming structures that exceed “minor” maintenance thresholds or do not meet the narrow exceptions in § 22.68.030(b). The Minor CUP procedures and required findings are in § 22.56.020–040. ---

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