Union City, CA Accessory Structures: ADU Impact Fees (2026)
Key Facts
- Fee threshold
- 750 sq ft or larger
- Fee basis
- Proportional to ADU/primary sq ft
- Exempt
- ADUs under 750 sq ft
- State floor
- Gov. Code § 66324
Summary
Union City charges impact fees on accessory dwelling units of 750 square feet or larger, prorated to the ADU's share of the primary home's square footage; smaller ADUs are fee-exempt.
ADUs that are 750 square feet or larger shall be subject to all applicable impact fees. Impact fees shall be charged proportionally in relation to the square footage of the primary dwelling unit. As ascribed in Government Code Section 66324, as the same may be amended from time to time, and reprinted here for reference, "impact fee" means: A "fee" as defined in subdivision (b) of [Government Code] Section 66000, expect that it also includes fees specified in [Government Code] Section 66477. "Impact fee" does not include any connection fee or capacity charge charged by a local agency, special district, or water corporation.
G. Passageway. No passageway shall be required in conjunction with the construction of an ADU. As ascribed in Government Code Section 66313, as the same may be amended from time to time, and reprinted here for reference, "passageway" means: A pathway that is unobstructed clear to the sky and extends from a street to one entrance of the ADU.
H. Separate Sale. Except as permitted by Government Code Section 66341, as the same may be amended from time to time, ADUs shall not be sold or conveyed separately from the primary dwelling.
I. Sewage. ADUs using a private sewage disposal system shall obtain approval by the local health officer.
J. Short-Term Rental Limitation. ADUs shall not be rented for a term of less than 30 days.
K.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4940544; v16 updated 2026-06-23).
Full Breakdown
Union City charges impact fees on accessory dwelling units under Union City Municipal Code § 18.34.030(F), but only once the ADU reaches 750 square feet or larger: anything smaller is exempt, matching the floor set by Government Code Section 66324. For ADUs that owe the fee, the City charges it proportionally to the ADU's square footage relative to the primary dwelling rather than a flat per-unit rate. The chapter reprints the state definition of "impact fee" so applicants can see exactly which charges qualify and which connection or capacity charges are excluded.
Violations & Fines
Building an ADU of 750 square feet or more without paying the applicable impact fee blocks issuance of the building permit; the fee must be paid before permit issuance under this chapter's general fee provisions.
Frequently Asked Questions
Do all Union City ADUs pay an impact fee?
How is Union City's ADU impact fee calculated?
Sources & Official References
Other rules in Union City
California rules heatmap·Compare Union City to another location·View the California accessory structures overview
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ADU Impact Fees in Nearby Cities
How other cities in Alameda County handle adu impact fees.