Foster City — Nonconforming Uses

Last reviewed: July 2, 2026

Overview

This page explains how Foster City treats nonconforming uses, nonconforming structures, and nonconforming lots under its zoning code (Title 17). It summarizes the rules that control continuation, repair, enlargement, destruction/rebuild, abandonment, time-for-conformance, and special rules for fences and small‑value buildings — all grounded in the Foster City Municipal Code. Key controlling rules are in § 17.70.010 – § 17.70.130.

Note: links below point to other Foster City topic pages you may need (planning, standards, parking, ADUs, etc.) as referenced in the local code: the page links the first natural mention of each topic inline.

How to read this page

• Every legal requirement below is tied to the city code and shows the controlling code citation (the § number) and the file-search citation for the ordinance text.
• When the code does not state an item or the uploaded ordinance is silent, I note “Not found in retrieved materials” and recommend you Verify with the jurisdiction.

What the code says — core rules (plain-English synthesis)

• Continuation and abandonment: legally existing nonconforming uses and structures may continue, but they may not be extended to occupy a larger area than existed when the ordinance became effective. If a nonconforming use is wholly discontinued for any reason for six months, it is conclusively presumed abandoned and any new use must conform to current rules (§ 17.70.010) .

• Undeveloped land used inconsistently at adoption: an otherwise nonconforming use of land with no building may continue only for five years from adoption; after that the land must be used in conformity (§ 17.70.030) .

• Alterations and repairs to nonconforming buildings:

  • Ordinary maintenance and repairs are allowed provided they are not structural and do not exceed 15% of fair market value in any one-year period; other repairs/alterations require a use permit (§ 17.70.100) .
  • A nonconforming building may have portions replaced or repaired so long as replacement work does not exceed 25% of the building’s market value (appraised by a city‑selected qualified appraiser) — otherwise enlargement or structural alteration must comply with current district rules (§ 17.70.040) .
  • Before any replacement, substantial alteration, repair, rebuild or similar action on a nonconforming structure, a permit must be secured from the planning commission or the community development director as appropriate (§ 17.70.050) .

• Destruction and restoration: if a nonconforming building is destroyed by casualty to the extent of more than 50% of its market value, it may only be restored if the restored building complies with current district regulations, except for a limited exception for some pre‑1972 residential dwellings (§ 17.70.060) .

• Time for conformance: some nonconforming buildings must be removed or converted to a conforming use when they reach specific ages determined by building type; these time-for-conformance ages are 15, 20, or 30 years depending on the building classification (see § 17.70.090) and no removal/alteration is required before 15 years from adoption of the ordinance (§ 17.70.080 – § 17.70.090) .

• Small‑value structures: any structure that had an assessed valuation of $3,000 or less when it became nonconforming must be removed or altered to comply within five years of becoming nonconforming; owners must receive at least one year notice before enforcement (§ 17.70.110) .

• Redistricting: rules apply equally to properties that become nonconforming because of later zoning map changes (§ 17.70.120) .

• Fences/walls/hedges: legally existing fences and walls that do not meet current standards are considered legal nonconforming and may remain until 25% of the fence/wall area is replaced or remodeled — at that point they must be brought into compliance with Chapter 17.52 and undergo architectural review; hedges have specific pruning/registration exceptions (§ 17.70.130) .

• Use permits: any use that requires a use permit under Title 17 is considered nonconforming until a use permit is obtained (§ 17.70.070) .

• Enforcement and penalties: continued nonconforming violations can trigger daily infractions and fines; penalty fees for correcting violations generally do not apply when bringing a legal nonconforming use into compliance (§ 17.06.160, § 17.06.175) .

District-by-district breakdown (where nonconforming rules matter)

Note: the nonconforming-use rules in Chapter 17.70 apply citywide across Foster City zoning districts. Below I list representative Foster City districts, their purpose, sample permitted uses/dimensions, and where those rules intersect with nonconforming treatment. For full use lists or numeric tables consult the cited district sections.

• R (Residential districts — e.g., R-1, R-3, R-4, R-T)

  • Purpose: single‑ and multi‑family residential development and associated accessory uses. See general ADU rules and multifamily standards in the ADU chapter.
  • Typical permitted uses: single‑family dwellings, accessory uses, multifamily where zoned. (See specific district chapters under Title 17.) Notably, substandard parcels in “R” districts may be allowed single‑family construction if the parcel was in single ownership at adoption and a use permit is obtained (§ 17.48.010) .
  • Key dimensional standards (examples): side/rear setbacks for ADUs are typically 4 ft (detached/attached ADU minimums), ADU height limits commonly 16–25 ft depending on ADU type, and special ministerial approval timelines apply to ADUs (ADU chapter §§ noted below) — see ADU provisions (ADU chapter §§, e.g., 17.78.090–17.78.100) for specifics.
  • Nonconforming implications: nonconforming homes can be repaired/maintained under § 17.70.100 and partially replaced under § 17.70.040 (value thresholds). ADUs: the city’s ADU rules say an applicant shall not be required to correct nonconforming zoning conditions as a condition of getting an ADU permit (ADU chapter, e.g., “Notwithstanding …” provision) .

• C‑1 (Neighborhood Commercial) — § 17.24

  • Purpose: small neighborhood commercial uses serving surrounding residential areas. Typical provisions require enclosed uses and restrict siting near residential boundaries. See § 17.24.040 – § 17.24.060 for permitted uses, dimensional rules and the enclosure requirement.
  • Typical permitted uses: retail, services that are compatible with neighbors; when abutting residential zones additional separation rules apply (§ 17.24.040) .
  • Dimensional standards (example): table in § 17.24.040 shows building site min width 50 ft, min lot area 5,000 sq ft, 0 ft front/side/rear in core areas but 28 ft minimum to adjacent residential zones in some cases; max building height references in the table appear and should be confirmed in the code for the lot.
  • Nonconforming implications: a C‑1 building or use that is nonconforming follows Chapter 17.70 for repairs, rebuilds, and abandonment; enclosure rules and parking requirements (Chapter 17.62) still govern when converting uses (§ 17.24.050). Use permit rules for conditional uses also interact with nonconforming designations (§ 17.70.070) .

• C‑2 (General Business) — Chapter 17.26

  • Purpose: broader commercial activities; see § 17.26.040 for area/bulk/yard rules and § 17.26.050 for parking/loading.
  • Nonconforming implications: any structural or use change to a nonconforming C‑2 building must follow § 17.70 (value thresholds, permit requirements). Consult the C‑2 chapter for permitted/conditional uses before attempting a change of use.

• P‑F (Public Facilities) — § 17.32

  • Purpose: government, public service, institutional uses. Permitted uses and special ADU allowances (on properties owned by religious institutions or schools) are listed in § 17.32.020 – § 17.32.050.
  • Nonconforming implications: public facilities that become nonconforming because of redistricting or ordinance changes are covered by Chapter 17.70, including time-for-conformance rules (e.g., § 17.70.080–090) and permit requirements for substantial repairs (§ 17.70.050) .

• OSC (Open Space & Conservation) — § 17.34

  • Purpose: protect open space, water‑oriented uses, parks. Permitted uses are limited and listed in § 17.34.020 – § 17.34.050.
  • Nonconforming implications: uses/structures legally existing prior to an ordinance change remain nonconforming under Chapter 17.70, but any expansion is prohibited unless made compliant with current rules (§ 17.70.010) .

If you need a district not listed above (e.g., CM, R‑T, R‑4), Verify with the jurisdiction and consult the specific district chapter in Title 17 for the exact permitted uses and dimensional standards; Chapter 17.70 applies across districts. Not found in retrieved materials: a complete, single-table list matching every Foster City zoning district to every dimensional standard was not present in the snippets I extracted; consult the full Title 17 district chapters for parcel‑specific standards. Verify with the jurisdiction.

Quick reference table — most decision‑relevant nonconforming standards

How these rules intersect with other local procedures (links)

• The basic zoning map and district rules are in the Foster City Foster City Zoning materials; Chapter 17.70 applies across those districts.
• When a repair or alteration requires discretionary review you will engage the Foster City Design Review and/or the planning commission per § 17.70.050.
• If your project changes parking demand, consult Foster City Parking rules; district chapters (e.g., § 17.24.050) reference Chapter 17.62 for parking.
• Nonconforming zoning conditions do not automatically block ADU permits: the ADU chapter says an applicant shall not be required to correct nonconforming conditions as a condition of obtaining an ADU permit (ADU chapter “Notwithstanding …” provision) — see the ADU chapter for details. See Foster City ADUs and the ADU chapter §§.
• For dimensional questions (setbacks, lot coverage, height), consult the Foster City Development Standards and the specific district chapter (e.g., § 17.24.040 for C‑1).
• If a property became nonconforming due to rezoning, Chapter 17.70 explicitly covers redistricting situations; see Foster City Overlay Districts if an overlay changed rules.
• Building and safety standards (Title 24) remain separate — see the California Building Standards Code page; the Foster City ADU chapter explicitly requires compliance with Title 24 where applicable.

(Those links are the first natural mention of each related topic on this page. Use them to jump to the relevant GoCodebook pages.)

Checklist — what an applicant must satisfy (practical, step‑by‑step)

• Confirm whether the existing use/structure was legally established at the time the current ordinance became effective (determine historic permits/records). Verify with the jurisdiction. (Relevant: § 17.70.010)
• If you plan structural repair/replace/enlargement, prepare to secure a permit from the planning commission or community development director as required by § 17.70.050.
• Commission or obtain/prepare a fair‑market‑value appraisal for the building (city selects appraiser per code) if approaching the 25% replacement threshold or the 50% destruction threshold. (Relevant: § 17.70.040, § 17.70.060)
• Calculate recent repair/replacement costs to confirm you are under the 15% per year ordinary‑repair cap before proceeding without discretionary review. (Relevant: § 17.70.100)
• If a use has been inactive, confirm it has not been “wholly discontinued” for 6 months (otherwise it’s presumed abandoned). (Relevant: § 17.70.010)
• For fences/walls: determine if replacement/remodel will exceed 25% of area, which will trigger compliance with Chapter 17.52 and architectural review (§ 17.70.130).
• If the building was destroyed by casualty, determine percent destruction vs. market value and consult § 17.70.060 before rebuilding.
• Check whether the property is in a district with special rules (e.g., PF, OSC, ADU exceptions) — consult the district chapter cited above. Verify with the jurisdiction.
• Factor in enforcement and potential daily fines for ongoing violations; consult § 17.06.160 if there is an active nonconforming violation.

Risks & Ambiguities

Plain‑English summary

If a use or building in Foster City doesn’t match today’s zoning, you usually may keep it — but you can’t expand it, and if it’s abandoned for six months, it’s lost. Small repairs are allowed, but big fixes, partial rebuilds above value thresholds, or rebuilding after serious destruction often require city approval; every threshold and deadline is governed by Chapter 17.70 (nonconformities) and related district chapters. Verify parcel specifics with the planning department. (See § 17.70.010 – § 17.70.130.)

Source References

• Foster City Municipal Code — Chapter 17.70 (Nonconformity Uses): § 17.70.010 – § 17.70.130.
• Foster City Municipal Code — Nonconforming alteration details: § 17.70.040 – § 17.70.050.
• Foster City Municipal Code — Time for conformance and repair caps: § 17.70.080 – § 17.70.100.
• Foster City Municipal Code — Small‑value structure rule: § 17.70.110.
• Foster City Municipal Code — Fences/walls/hedges: § 17.70.130 and Chapter 17.52.
• Foster City Municipal Code — District examples: § 17.24.040 (C‑1), Chapter 17.26 (C‑2), § 17.32.020 (P‑F), Chapter 17.34 (OSC).
• Foster City Municipal Code — Substandard parcel rule: § 17.48.010.
• Foster City Municipal Code — ADU provisions (applicable nonconforming language): ADU chapter (ADU ministerial/permit provisions and the “not required to correct nonconforming conditions” clause). (See ADU chapter provisions, e.g., the “Notwithstanding …” clause in the ADU chapter.)
• Foster City Municipal Code — Enforcement and penalties (daily infractions): § 17.06.160 – § 17.06.175.

Retrieved passages

• Foster City Zoning Code (§ 4) High relevance show source text
• Foster City Zoning Code (§ 4) High relevance show source text
• CBC § 4 (§ 4) High relevance show source text
• Foster City Zoning Code (Chapter 17.70) High relevance show source text
• CBC § 4 (chapter by) High relevance show source text
• Foster City Zoning Code (§ 3) High relevance show source text
• Foster City Zoning Code (§ 4) Medium relevance show source text
• Foster City Zoning Code (chapter shall) Medium relevance show source text
• Foster City Zoning Code (§ 66314) High relevance show source text
• Foster City Zoning Code (§ 66333) Medium relevance show source text
• CBC § 66321 (§ 66321) Medium relevance show source text

Cited sections

• Foster City Municipal Code — Chapter 17.70 (Nonconformity Uses): **§ 17.70.010 – § 17.70.130**. (Chapter 17.70)
• Foster City Municipal Code — Nonconforming alteration details: **§ 17.70.040 – § 17.70.050**. (§ 17.70.040)
• Foster City Municipal Code — Time for conformance and repair caps: **§ 17.70.080 – § 17.70.100**. (§ 17.70.080)
• Foster City Municipal Code — Small‑value structure rule: **§ 17.70.110**. (§ 17.70.110)
• Foster City Municipal Code — Fences/walls/hedges: **§ 17.70.130** and Chapter **17.52**. (§ 17.70.130)
• Foster City Municipal Code — District examples: **§ 17.24.040 (C‑1)**, **Chapter 17.26 (C‑2)**, **§ 17.32.020 (P‑F)**, **Chapter 17.34 (OSC)**. (§ 17.24.040)
• Foster City Municipal Code — Substandard parcel rule: **§ 17.48.010**. (§ 17.48.010)
• Foster City Municipal Code — ADU provisions (applicable nonconforming language): ADU chapter (ADU ministerial/permit provisions and the “not required to correct nonconforming conditions” clause). (See ADU chapter provisions, e.g., the “Notwithstanding …” clause in the ADU chapter.) (chapter provisions)
• Foster City Municipal Code — Enforcement and penalties (daily infractions): **§ 17.06.160 – § 17.06.175**. (§ 17.06.160)
• FosterCity_ZoningCode.md

• Official Foster City code library