Millbrae — Nonconforming Uses

Last reviewed: July 2, 2026

Overview

This page explains how Millbrae treats nonconforming lots, uses, and structures under the Millbrae Zoning Code (Title 10). It synthesizes the rules for continuance, change, abandonment, repair/alteration, and special amortization for certain uses — and points to the specific code sections you must cite on applications. Key rules are in § 10.05.2400 through § 10.05.2450 and the adult‑oriented business chapter (Chapter 10.35).

Note: for zoning district definitions and dimensional standards referenced below, see the Millbrae land‑use table and development standards. The city’s land‑use matrix is at § 10.05.0410 and development standards appear in district subsections (examples cited below).

How to read this page

• Bolded district names (for example R-1, C) indicate Millbrae's actual zoning districts.
• The first natural mention of related topics is hyperlinked to the GoCodebook Millbrae menu so you can quickly jump to parking, design review, ADUs, etc.: Millbrae zoning & planning overview, Millbrae Zoning, Millbrae Land Use, Millbrae Development Standards, Millbrae Parking, Millbrae Design Review, Millbrae Overlay Districts, Millbrae ADUs, California Building Standards Code.

What Millbrae’s code actually says (short answers)

• Existing nonconforming lots, uses, and structures may continue but may not be enlarged to occupy more area than they did when they became nonconforming (§ 10.05.2400).
• A nonconforming use may be changed only to another nonconforming use of the same or a more restrictive classification with a conditional use permit; once replaced by a more restrictive nonconforming use it cannot revert (§ 10.05.2420).
• If a nonconforming use is wholly discontinued for ninety (90) days, it is deemed abandoned and future uses must conform, except for specific exceptions (court order, required upgrades/retrofits, ADA/fire safety work) (§ 10.05.2420).
• Nonconforming structures generally cannot be enlarged, extended, reconstructed, or structurally altered except in limited cases (CUP where extent increases but degree not intensified; replacement/restoration >50% for nonresidential buildings; certain repairs and single‑family work treated ministerially) (§ 10.05.2430) .
• Rezoning that creates a nonconformity is covered: uses requiring a conditional use permit are treated as nonconforming until the CUP is obtained (§ 10.05.2440).
• Adult‑oriented businesses created nonconforming by minimum‑distance rules have a specific amortization and extension process (limited continuation, then termination unless an extension is granted) (Chapter 10.35, especially § 10.35.040–10.35.050).

District-by-district breakdown (where nonconformity rules apply)

Below are the primary districts used across Millbrae’s land‑use table. For full use lists, consult the land‑use table at § 10.05.0410.

R-1LL (Single-family, large-lot)

• Purpose: preserve low‑density single‑family neighborhoods.
• Typical permitted uses: single‑family dwellings, accessory buildings. (See land‑use matrix, § 10.05.0410.)
• Key dimensional standards (examples for single‑family districts): front setback 20 ft, side interior 5 ft / minimum 3 ft in narrow lots, rear 10 ft, maximum height 30 ft (see residential development standards in Articles V–VII for exact limits per subdistrict).
• Where it applies: typical single‑family neighborhoods outside the specific plan areas. Nonconforming single‑family structures have more ministerial repair allowances under § 10.05.2430 (single‑family work that does not extend or intensify the nonconformity may proceed via building permit).

R-1, R-2, R-3 (Single‑family and multi‑family residential)

• Purpose: gradation from single‑family to multi‑family housing.
• Typical uses: duplexes, triplexes, multifamily (permitted/conditional per table).
• Key dimensional standards: R-2/R-3 front setbacks frequently 20 ft, side setbacks 5 ft interior / 10 ft exterior, rear 10–15 ft, heights commonly 30 ft or as specified in the district standards. See Articles V–VII.
• Practical effect: nonconforming residential lots (undersized parcels) may be developed to the maximum degree possible while complying with applicable regulations (§ 10.05.2410).

C (Commercial)

• Purpose: retail, offices, services along commercial corridors.
• Typical permitted uses: retail, restaurants, offices; larger or special uses may require conditional use permits; adult‑oriented businesses restricted by Chapter 10.35.
• Key dimensional standards: minimum lot width 25 ft, minimum lot area 2,500 sf, height limit 40 ft (with planning commission height exceptions) and setbacks: typically none but 10 ft where adjacent to an alley or any “R” district (§ 10.05.1020).
• Practical effect: commercial buildings that become nonconforming may not be expanded to increase the nonconforming area without compliance mechanisms such as CUPs or exceptions identified in § 10.05.2430.

I (Industrial)

• Purpose: manufacturing, warehousing, heavy uses.
• Typical permitted uses: light and heavy manufacturing, warehousing, vehicle services (see the land‑use table).
• Practical effect: nonconforming industrial uses remain allowed subject to the same continuation rules; certain uses (e.g., adult‑oriented) have amortization rules under Chapter 10.35 that may limit continuance in time.

PD (Planned Development), DTECRSP (Downtown & El Camino Real Specific Plan), MSAPD (Millbrae Station Area PD) — special plan districts

• Purpose: site‑specific development plans and design standards tailored to an approved project.
• Typical permitted uses: as defined by the approved PD or specific plan documents (uses may differ from base zoning). See the land‑use matrix notes at § 10.05.0410.
• Practical effect: when rezoning or a PD creates a nonconformity, the general nonconformity rules apply; also, many PD approvals include their own development plan conditions that supersede or modify standard district rules — verify the approved PD documents. § 10.05.2440 applies to rezoning‑created nonconformance.

Quick reference table — Decision‑relevant nonconformity rules

Practical guidance and interpretation notes

• If you want to change a nonconforming commercial or industrial use to another nonconforming use, plan to pursue a conditional use permit; the code explicitly conditions such changes on the CUP process (§ 10.05.2420).
• Repairs to single‑family dwellings that do not extend or intensify the nonconformity are handled ministerially (building permit); if the work would alter the single‑story character it triggers architectural/design review (§ 10.05.2430) — check Millbrae Design Review for process.
• Large reconstructions or expansions for nonresidential buildings (replacement/restoration > 50% of total SF) may require a CUP (§ 10.05.2430).
• When a property becomes nonconforming because of a rezoning or overlay, the same nonconforming rules apply; also, an existing use that now requires a CUP is treated as nonconforming until the CUP is obtained (§ 10.05.2440). Always verify whether an overlay district (for example within the Millbrae Station Area PD) imposes additional rules: see Millbrae Overlay Districts.

Checklist — what an applicant must include / satisfy

• Demonstrate the nonconforming status and date the nonconformity arose (e.g., prior permits, business records, site photos). See § 10.05.2400.
• If proposing a change of use to another nonconforming use, prepare a Conditional Use Permit application (narrative, site plan, operational details) as required by § 10.05.2420 and Article XXV procedures.
• If proposing structural work on a nonconforming building, show calculations demonstrating the work does not “increase the extent or intensify the degree” of nonconformity or include CUP justification where required (§ 10.05.2430).
• For single‑family dwellings, document that the proposed repairs/alterations do not extend/intensify nonconformity or note that architectural review may be required (§ 10.05.2430 and § 10.05.2500).
• For adult‑oriented businesses seeking continuation or extension, include evidence of investment and relocation efforts as required for an extension under § 10.35.050.

Risks & Ambiguities

Plain‑English summary

If your Millbrae property or business doesn’t meet today’s zoning rules, you can usually keep using it — but you generally cannot enlarge the nonconforming part, you risk losing nonconforming status after 90 days of total discontinuance, and changes to a different nonconforming use normally require a conditional use permit (§ 10.05.2400–.2430). For specified uses like adult‑oriented businesses special amortization rules also apply (Chapter 10.35).

Source References

• Millbrae Zoning — Article XXIV, “Nonconformities” (general, lots, uses, structures): § 10.05.2400, § 10.05.2410, § 10.05.2420, § 10.05.2430.
• Millbrae Zoning — Nonconformance due to rezoning and effect on construction underway: § 10.05.2440, § 10.05.2450.
• Millbrae Zoning — Land use table and district listings: § 10.05.0410 (land‑use matrix).
• Millbrae Zoning — Commercial district development standards (example): § 10.05.1020.
• Millbrae Zoning — Residential development standards / setbacks and height examples: Article V–VII excerpts (see § 10.05.0520, § 10.05.0720).
• Millbrae Zoning — Design review and CUP procedures (Article XXV): § 10.05.2500.
• Millbrae Code — Adult‑oriented businesses, amortization and extension: § 10.35.030, § 10.35.040, § 10.35.050.
• Millbrae code source: Millbrae Zoning Code (download copy, eCode360). Downloaded from https://ecode360.com/MI4538 on 2026‑05‑11.
• State ADU/Nonconforming guidance (uploaded): 2025 California ADU handbook (for ADU‑nonconformance interactions).

Retrieved passages

• CBC § 2 (§ 2) High relevance show source text
• Millbrae Zoning Code (§ 10.35.040.) High relevance show source text
• Millbrae Zoning Code (§ 10.05.2400) High relevance show source text
• CBC § 10.05.2430 (§ 10.05.2430) High relevance show source text
• Millbrae Zoning Code (Article XXIV) High relevance show source text
• Millbrae Zoning Code (§ 8362) High relevance show source text
• Millbrae Zoning Code (§ 10-7.102) High relevance show source text
• Millbrae Zoning Code (§ 10.35.030.) Medium relevance show source text

Cited sections

• Millbrae Zoning — Article XXIV, “Nonconformities” (general, lots, uses, structures): **§ 10.05.2400**, **§ 10.05.2410**, **§ 10.05.2420**, **§ 10.05.2430**. (Article XXIV)
• Millbrae Zoning — Nonconformance due to rezoning and effect on construction underway: **§ 10.05.2440**, **§ 10.05.2450**. (§ 10.05.2440)
• Millbrae Zoning — Land use table and district listings: **§ 10.05.0410** (land‑use matrix). (§ 10.05.0410)
• Millbrae Zoning — Commercial district development standards (example): **§ 10.05.1020**. (§ 10.05.1020)
• Millbrae Zoning — Residential development standards / setbacks and height examples: Article V–VII excerpts (see § 10.05.0520, § 10.05.0720). (Article V)
• Millbrae Zoning — Design review and CUP procedures (Article XXV): **§ 10.05.2500**. (Article XXV)
• Millbrae Code — Adult‑oriented businesses, amortization and extension: **§ 10.35.030**, **§ 10.35.040**, **§ 10.35.050**. (§ 10.35.030)
• Millbrae code source: Millbrae Zoning Code (download copy, eCode360). Downloaded from on 2026‑05‑11.
• State ADU/Nonconforming guidance (uploaded): 2025 California ADU handbook (for ADU‑nonconformance interactions).
• Millbrae_ZoningCode.md
• 2025 California ADU handbook.md

• Official Millbrae code library