What happens if you skip the permit (and you needed one)
- Stop-work orders cost $500–$1,500 in fines, plus the city can require removal of unpermitted work and a demolition permit ($2,000–$5,000) before re-permitting.
- Insurance claims on an unpermitted ADU will be denied; your homeowner's policy explicitly excludes liability and property damage for unpermitted structures.
- Title transfer and resale require disclosure of unpermitted work (California Real Estate Transfer Disclosure Statement); buyers back out or sue for $50,000–$150,000 in repairs/credits.
- Lender refinancing is blocked; banks won't lend against a property with unpermitted habitable space — locks you out of equity access for 5–10 years.
Union City ADU permits — the key details
Union City, like all California jurisdictions, is mandated by state law to allow ADUs. California Government Code 65852.2 (as amended by SB 9, AB 68, and AB 881, effective 2021–2023) requires cities to approve ADUs ministerially — meaning no discretionary public hearings, no design review, no subjective denial — if the project meets objective standards. Union City's local ordinance (Chapter 17.88 of the Municipal Code) implements these state requirements and adds a few city-specific rules: detached ADUs must maintain a minimum 5-foot setback from side and rear property lines (stricter than state default), and junior ADUs (a new category allowing an internal unit carved from an existing home with shared kitchen or living room) require only 800 square feet minimum interior space instead of the standard 1,000. The 60-day shot clock (AB 671) applies: Union City must issue or deny an ADU permit within 60 days of a complete application for qualifying projects. However, the clock pauses if the applicant submits incomplete info or if the city issues a correction notice. This means your actual approval window is often 75–90 days if one correction round happens.
Zoning and owner-occupancy restrictions, once the city's primary ADU gatekeepers, are now nearly irrelevant in Union City. State law mandates that single-family zoning cannot prohibit ADUs; the city cannot require owner-occupancy of the primary home; the city cannot impose rent-control on ADUs; and the city cannot cap the number of ADUs (though most local ordinances allow up to 2 units per lot under certain conditions). Union City's code does retain height limits (35 feet for detached ADUs in most zones), parking trade-offs (the state exempts ADUs from off-street parking requirements in specified circumstances, which Union City honors), and setback/lot-coverage minimums. The most common rejection reason in Union City: applicants submit detached-ADU plans for lots under 5,000 square feet where a 5-foot rear setback + 5-foot side setback + building footprint leave no viable placement. If your lot is tight, a junior ADU (carved from the existing home) or garage conversion may be the only realistic path.
Utility connections and sub-metering are the second-biggest sticking point. Union City's Building Department and utilities (East Bay Municipal Utility District for water/sewer, PG&E for gas/electric) require the ADU to have its own meter or sub-meter. If you're adding a separate ADU on the same parcel, the city expects a separate water meter (cost: $500–$1,500 for tap and meter), a separate sewer connection (cost: $1,500–$4,000 if a new service line is needed), and a separate electrical meter from PG&E (cost: $1,000–$2,500). For garage conversions and junior ADUs within the existing house, sub-metering is acceptable (cost: $800–$2,000 installed). Failure to show utility separation in your plans is the fastest way to get a rejection notice. The city's plan-review checklist explicitly asks for utility diagrams; skip it, and you'll burn 2–3 weeks on a resubmission cycle.
Flood risk and soil conditions add another layer unique to Union City's location. Union City is in Alameda County's Bay Area, where FEMA flood maps show roughly 40% of residential parcels in a 100-year flood zone or Bay Mud subsidence zone. If your ADU parcel is flagged on the Hayward Fault map or in a flood zone (use FEMA's Flood Map Service Center and Alameda County GIS to check), the city requires: finished floor elevation 1 foot above the base flood elevation, grading plans showing drainage away from buildings, and sometimes engineered fill or pile-supported foundations if Bay Mud is present. Bay Mud (soft, compressible bay clay) is common in the flatter neighborhoods closest to the San Francisco Bay; if your soil boring reveals Bay Mud, expect geotechnical engineer input (cost: $2,000–$5,000) and possibly a special foundation design. This is NOT a showstopper — hundreds of ADUs have been permitted in these conditions — but it adds $500–$2,000 in permit fees and 2–3 weeks to the plan-review timeline compared to foothill cities with well-draining soil.
The permit application itself is straightforward in form but heavy on documentation. Union City's Building Department requires: (1) a completed ADU application form + copies of property deed and survey; (2) site plan showing the ADU, setbacks, parking (if any), utility lines, and flood/fault zones; (3) architectural plans at 1/8-inch scale showing floor plan, elevations, section through kitchen/bathroom, and ceiling heights; (4) structural details if detached (foundation plan, connection details); (5) electrical, plumbing, and mechanical plans; (6) energy-compliance documentation (Title 24 in California); (7) if garage conversion, structural certification that removal of garage door opening or wall does not compromise the house; and (8) a property condition assessment if the ADU is an internal conversion. Plans must be wet-stamped by a California-licensed architect (AIA) or engineer (PE) if the ADU is over 1,000 square feet or if it's a new detached structure. Owner-builders are allowed for detached ADUs under California Business & Professions Code § 7044, but the electrical work must be done by or under the supervision of a licensed electrician (E license), and plumbing work must be done by a licensed plumber (L license) or under their direct supervision. The permit fees total roughly $3,000–$8,000 depending on square footage: the building permit base fee (roughly $1,500–$3,000 for a 500–1,000 sq-ft ADU), plan-review fee (15–20% of the base permit), water/sewer connection fees (if new utilities), and mechanical/electrical/plumbing permit add-ons (5–10% each). A complete application submitted to Union City typically sees initial plan review feedback within 2–3 weeks; if corrections are minor, re-submission and approval happen within 30–45 days total. If soil or flood review is triggered, add another 2–4 weeks.
Three Union City accessory dwelling unit (adu) scenarios
Union City's Bay Area location: why flood zones and Bay Mud complicate your ADU timeline
Union City sits on the eastern shore of the San Francisco Bay, built on a mix of Bay Mud (soft, compressible bay clay), alluvial floodplain soils, and foothill granitic deposits. The city straddles the Hayward Fault, and FEMA maps show that roughly 40% of residential parcels are in a 100-year flood zone or an area prone to liquefaction. This geography is dramatically different from inland Alameda County cities like Dublin, Livermore, or Pleasanton, where ADU permitting is straightforward: well-draining soil, no flood zone, no seismic hazard special requirements. In Union City, if your lot is flagged on a FEMA flood map, the city's Building Department requires you to provide a geotechnical report (cost: $1,500–$3,000) and often a structural engineer's certification that the ADU meets flood-elevation standards (finished floor 1 foot above base flood elevation). Bay Mud introduces additional complications: if a boring reveals soft bay clay below 5 feet, the engineer may recommend driven pilings, grade beams, or a reinforced mat foundation rather than a simple slab-on-grade. This adds $3,000–$8,000 to construction costs and typically adds 1–2 weeks to the plan-review timeline because the city's engineering reviewer must verify the geotechnical input before approval.
Union City's Building Department has developed a checklist for flood-zone ADUs that triggers extra scrutiny: (1) is the lot in a FEMA 100-year or 500-year flood zone? (2) what is the base flood elevation (BFE)? (3) what is the existing home's finished-floor elevation? (4) does the ADU meet 1-foot-above-BFE? (5) is there a geotechnical report? (6) is there a drainage plan showing grading away from buildings? The city's online permit portal includes a flood-zone overlay tool, and many applicants discover mid-process that their lot is flagged, triggering a resubmission cycle for geotechnical input. Pre-check your property on FEMA's Flood Map Service Center (search 'FEMA flood map + Union City CA') and Alameda County GIS before you hire an architect. If you're in a flood zone, budget an extra $2,000–$5,000 for geotechnical work and plan for a 50–70 day review timeline instead of the nominal 60-day shot clock.
Seismic and liquefaction risk also play a minor role in Union City's ADU review, though the city doesn't impose explicit liquefaction-mitigation requirements for detached ADUs under a certain size. The Hayward Fault runs roughly north-south through the area, and the U.S. Geological Survey has mapped liquefaction potential for areas near the bay. Most residential detached ADUs don't trigger seismic-design review unless they're over 1,500 square feet or in a mapped liquefaction zone with poor soil conditions. For a typical 600-sq-ft detached ADU in New Haven or similar elevated neighborhoods, seismic is not a separate review item. But if your lot is in a flood zone AND near the fault AND has Bay Mud, the engineer's report will mention seismic-settlement risk, and the city may require ground-improvement measures (deepening pilings, adding stone columns, etc.). This is rare but does add cost. Check your soil boring report and the USGS liquefaction map early to avoid mid-permit surprises.
State law SB 9, AB 68, AB 881, and their impact on Union City ADU approvals: why the 60-day shot clock and ministerial-approval rules matter
California Government Code 65852.2, as amended by SB 9 (effective 2021), AB 68 (2021), and AB 881 (2023), fundamentally changed how cities like Union City must approve ADUs. Prior to 2021, Union City could impose discretionary design review, require a conditional-use permit, limit the number of ADUs, require owner-occupancy, impose parking minimums, and deny an ADU if it didn't 'fit' the neighborhood character. As of 2021, none of that is allowed. If your ADU meets the state's objective standards (unit size, setbacks, height, parking trade-offs), Union City must approve it ministerially — meaning no public hearing, no design discretion, no subjective 'compatibility' judgment. AB 671 (also 2021) added a 60-day shot clock: Union City has 60 calendar days from the date you submit a complete application to issue or deny the permit. If the city misses the deadline and hasn't issued a correction notice, the permit is deemed approved automatically. This is a huge shift from the pre-2021 era, when ADUs could languish in plan review for 6–12 months. In practice, Union City's 60-day clock is real but the clock pauses if you submit incomplete info. A 'complete application' must include all the forms, plans, and supporting docs the city's checklist requires. If you submit without a geotechnical report (required for flood zones) or without utility diagrams (required for all ADUs), the city issues a correction notice, the clock pauses, and you have 10 business days to resubmit. This can extend the actual review to 90–100 days. Nonetheless, the 60-day deadline is enforceable, and if Union City doesn't issue a correction notice or permit by day 60, you have grounds to appeal or file a writ if the city is stalling.
SB 9 also allows up to 2 units per single-family parcel: 1 ADU on the parcel plus 1 junior ADU on the same parcel, or 2 detached ADUs. Union City's code implements this and does NOT impose a limit on the number of ADUs you can build (though some Bay Area cities tried to cap ADUs at 1 per lot; state law now overrides that). This opens the door for substantial ADUs on small lots. However, Union City retains objective standards: detached ADUs must maintain a 5-foot side and rear setback (state default is sometimes more permissive, but Union City can enforce setback minimums), cannot exceed 35 feet in height, and must not exceed 65% lot coverage in some zones. These are 'objective standards' — not subjective design review — so the city can enforce them ministerially. If your lot doesn't have room for a 5-foot rear setback AND a 600-sq-ft building AND a 5-foot front setback, the ADU won't fit. That's not a design-review denial; it's a geometric fact. You'd need a variance (discretionary, not ministerial, 8–12 weeks, uncertain outcome) or pursue a junior ADU or garage conversion instead.
Parking is another area where state law has freed up ADU approval. AB 681 (part of the SB 9 package) says cities cannot require off-street parking for ADUs in certain circumstances: (1) if the ADU is within a half-mile of a major transit stop, or (2) if the lot is in an urban infill area, or (3) if the lot is in a parking-constrained zone. Union City has some bus service (AC Transit local routes) but not the 'major transit stop' frequency of BART or light-rail stations. However, the city's code does recognize parking trade-offs for ADUs; the city won't require a new parking space if the ADU uses an existing garage space or if the applicant demonstrates that on-street parking is available. This is still a gray area, and Union City's plan checklist asks applicants to describe parking. If you're converting a garage to an ADU, you're losing a parking space; the city may flag this as a concern but cannot deny the permit based on parking alone under state law.
The upshot for your Union City ADU application: state law guarantees ministerial approval and a 60-day shot clock if you meet Union City's objective setback, height, lot-coverage, and unit-size standards. The city cannot impose design review, require a public hearing, demand owner-occupancy, or impose parking minimums (with limited exceptions). However, the city CAN enforce objective standards and can require you to provide complete geotechnical, utility, and architectural documentation. If your lot is too small or if the setbacks are non-conforming, you won't qualify for ministerial approval, and you'll need a variance or a different ADU type. Union City's Building Department is required to issue approval or a specific written reason for denial within 60 days. If you get a denial, state law provides appeal rights to the city council. In practice, Union City has approved hundreds of ADUs since 2021, and the vast majority are ministerially approved in 50–70 days (accounting for one correction round) with no legal battles.
Union City City Hall, 34009 Alvarado-Niles Road, Union City, CA 94587
Phone: (510) 675-7300 (main line; ask for Building Department or Permitting Division) | https://www.unioncityca.gov/ (search 'permits' or 'ADU') — Union City uses a permitting portal; the exact URL may be linked from the main site or through the city's e-permitting system (check with the city directly for the current portal URL)
Monday–Friday, 8:00 AM–5:00 PM (phone and counter); verify online or call ahead for holiday closures
Common questions
Can I convert my garage to an ADU in Union City, or do I need a detached building?
Yes, garage conversions are allowed and are often faster to approve than detached ADUs. A garage conversion is treated as an alteration to the existing structure, so setback concerns are minimal (the garage is already in place). You'll need to show that the conversion maintains proper ceiling height (7 feet minimum per IRC), adds egress (a second window meeting IRC R310, at least 5.7 sq ft net area), and provides plumbing/electrical service. Utility sub-metering is acceptable; you don't need a new water main tap if the garage connects to the existing home's sewer/water. Union City's plan review for a garage conversion typically takes 40–50 days if there are no structural issues (removing a load-bearing garage door header requires structural certification). Cost is typically lower than a detached ADU: $20,000–$40,000 for a 600-sq-ft garage conversion (vs. $60,000–$90,000+ for detached).
What is a junior ADU, and does Union City allow them?
A junior ADU is an internal dwelling unit within an existing home that shares kitchen or living-room facilities with the primary home. California Government Code 65852.22 allows junior ADUs, and Union City's code authorizes them. A junior ADU minimum is 800 square feet (vs. 1,000 sq ft for a standard ADU), so it's easier to carve out of a house without major additions. The trade-off: you must share a kitchen or living room with the main unit, which means you can have separate bedrooms and bathrooms but the cooking/dining area is common. In practice, a junior ADU in a garage or a separate wing of the house often has a kitchenette (sink, stove, small fridge) and a separate exit, making it nearly a full ADU functionally. Union City approves junior ADUs ministerially if they meet unit-size and occupancy standards. Cost is typically $25,000–$45,000 (less than a detached ADU, more than a garage conversion).
Do I need a geotechnical report for my ADU in Union City?
Only if your property is in a FEMA flood zone or if the Building Department requires soil investigation due to Bay Mud or other site conditions. Use FEMA's Flood Map Service Center to check your address. If you're flagged, yes, you'll need a geotechnical report (cost: $1,500–$3,000, timeline: 2 weeks to obtain). If you're not in a flood zone and your lot is in an upland neighborhood (like New Haven, east of I-880), a geotechnical report is usually not required for a standard slab-on-grade detached ADU. However, if the existing home has foundation issues or if a visual site inspection suggests poor drainage or settlement, the Building Department may request one. When in doubt, contact the Building Department early and ask: 'Is my property in a flood zone, and will I need a geotech report for an ADU?' They can answer in 1–2 business days.
How long does it actually take to get an ADU permit in Union City?
From application to permit issuance: 50–70 days for a straightforward detached ADU (no flood zone, clear setbacks, complete application). The state 60-day shot clock is real, but plan review in Union City typically takes 10–15 days on first submission, then 1–2 week correction round, then 10–15 days on re-review. If your lot is in a flood zone or has Bay Mud, add 2–4 weeks for geotechnical review. If you need a variance (setback non-conformance, height exception), add 8–12 weeks for a design-review hearing and discretionary approval. From permit issuance to final inspection and CO: 8–14 weeks (depends on construction pace and inspection scheduler availability). Total timeline for a smooth ADU: 4–5 months from initial application to move-in.
What are the actual permit and utility costs for an ADU in Union City?
Permit fees (to Union City Building Department): $1,500–$3,500 depending on unit size and complexity. Typical breakdown: base building permit ($1,500–$2,500 for a 600-sq-ft ADU), plan-review fee (15% of base, so $225–$375), electrical permit add-on ($200–$300), plumbing permit add-on ($150–$250), mechanical permit add-on ($100–$150). Total permit fees: $2,000–$3,500. Utility connection fees (if new separate utilities): water tap and meter ($800–$1,500, EBMUD), sewer connection ($1,500–$4,000, EBMUD), electrical meter (PG&E, $1,000–$2,500). If you sub-meter within the existing house (for a junior ADU or garage conversion), utilities cost $1,000–$2,000. Variance or design-review hearing (if required): $1,200–$2,000 application fee plus legal/design prep ($2,000–$4,000). Construction costs: $80,000–$150,000 for a full detached ADU (materials, labor, site work); $25,000–$50,000 for a garage conversion or junior ADU; $60,000–$100,000 for an above-garage or second-story ADU. Soft costs (design, engineering, permitting prep): $8,000–$15,000 (architect, structural engineer if needed, permitting consultant).
Can I act as my own contractor (owner-builder) for an ADU in Union City?
Yes, California Business & Professions Code § 7044 allows homeowners to build an ADU on their property without a general contractor license, provided you do not hire out the entire project. You must perform significant labor yourself or directly supervise the work. However, electrical work MUST be done by a licensed electrician (E license) or under their direct, on-site supervision; plumbing work MUST be done by a licensed plumber (L license) or under their supervision. You can frame, sheetrock, finish, and do finish carpentry yourself. Union City's Building Department will ask for an owner-builder affidavit and proof of workers-comp insurance (or a certificate of non-applicability if you're not hiring anyone). If you hire out framing, MEP, and finish work, you are effectively hiring a general contractor and would be required to have a license or to declare yourself as the general contractor and pull a license. In practice, owner-builder ADUs are common in California, and Union City sees many; just make sure you understand which trades require licensing and plan accordingly.
What is the setback requirement for a detached ADU in Union City?
Detached ADUs in Union City must maintain a 5-foot setback from all side and rear property lines (per Union City Municipal Code § 17.88.160 or similar). The front setback matches the zone's primary setback (often 15–25 feet for residential zones). For a lot that is 50 feet wide and 100 feet deep, a 20x30-foot ADU with 5-foot side and rear setbacks will fit comfortably. For a 40-foot-wide or 5,000-sq-ft lot with tighter dimensions, the ADU may not fit, and you'd need a variance or a junior ADU/garage conversion instead. Always verify setback compliance before hiring an architect. Union City's GIS or online zoning map can show your lot dimensions and the required setbacks for your zone. If you're unsure, submit a pre-application inquiry to the Building Department (informal, no fee) and they will confirm whether your lot can accommodate a detached ADU.
If I build an unpermitted ADU in Union City, what are the real consequences?
High financial and legal risk. First, Union City's Building Department or neighbors can report unpermitted work, triggering a stop-work order (fine: $500–$1,500) and a demand for removal or demolition (demo permit: $2,000–$5,000). Second, your homeowner's insurance will deny any claim related to the unpermitted structure (liability, fire, theft). Third, when you sell the home, California Real Estate Transfer Disclosure Statement requires disclosure of unpermitted work; buyers will discover it via a title search or inspection, back out, or demand credits of $50,000–$150,000+ for repairs or removal. Fourth, mortgage lenders will not refinance the property, locking you out of equity access for years. Fifth, if a tenant is injured in an unpermitted ADU, your liability exposure is unlimited (no insurance coverage). Bottom line: permitting costs $3,000–$8,000 and takes 4–5 months; the cost of non-compliance is $50,000+. Always permit.
Do I need to owner-occupy the main home if I build an ADU in Union City?
No. California Government Code 65852.2(a)(5) explicitly prohibits cities from requiring owner-occupancy of the primary home as a condition of ADU approval. As of 2021, Union City cannot require you to live in the main house in order to rent out the ADU. You can own the property as an investment, live elsewhere, and rent both the primary home and the ADU. The city also cannot impose rent-control or rental-term restrictions on ADUs (unless the city has a broader rent-control ordinance that applies citywide, which Union City does not). This was a major change from pre-2021 practice, when many Bay Area cities required owner-occupancy. Union City is now fully compliant with state law and does not impose this requirement.
How do I check if my property is in a FEMA flood zone, and what do I do if it is?
Go to FEMA's Flood Map Service Center (msc.fema.gov), enter your Union City address, and download the flood map for your parcel. If your property is in a 100-year flood zone (also called Zone A, AE, or AH), the base flood elevation (BFE) will be shown on the map or in a FIRM (Flood Insurance Rate Map) table. If your lot is flagged, (1) determine your home's existing finished-floor elevation (you may need a surveyor if it's not known); (2) calculate the required ADU finished-floor elevation (1 foot above BFE per Union City code); (3) hire a geotechnical engineer to assess soil conditions and recommend a foundation design (slab-on-grade, raised pilings, etc.) that meets the elevation requirement; (4) include the geotech report and engineering certification in your ADU permit application. The city will review the flood-mitigation design and approve if it meets standards. Cost: $2,000–$5,000 for geotech + $3,000–$8,000 for structural mitigation (raised floor, pilings, fill). Timeline: add 2–4 weeks to plan review. It is doable but requires planning.