Predictika · ADU and JADU project pre-screen, Union City, California

A permit intake assistant's ADU project, pre-screened before it goes to the permit counter

A permit intake assistant takes in a homeowner's accessory dwelling unit (ADU) project in Union City, California, and says it is ready for a building-permit application. Before it goes out, the assistant sends it to Predictika's validator, which checks it against California ADU law and the City of Union City's ADU rules together, applies state law where it overrides a stricter local rule, and reports every problem it finds in one pass.

Scope: ADU and junior ADU (JADU) projects on single-family and multifamily residential lots in Union City, California, pre-screened against California Government Code sections 66310 to 66342 and Union City Municipal Code Chapter 18.34 (Ordinance 2025-002), with state law prevailing where the two conflict. Rules as of September 30, 2026. A pre-screen, not a permit decision. See everything this validator covers

This validator pre-screens any ADU or JADU project on a residential lot in Union City against both sets of rules, not just the scenarios shown below.

  • Unit types and lots — conversion ADUs, new attached and new detached ADUs and JADUs on single-family lots, and conversions or detached ADUs on multifamily lots.
  • Size, height and setbacks — size limits by unit type, height limits (including the transit, roof-pitch and multistory exceptions), the two-story limit for an attached unit, the 4-foot side and rear setbacks, the 150 sq ft expansion limit for a conversion, and the front setback with the waiver for units of 800 sq ft or less.
  • How many units — one ADU and one JADU on a single-family lot, a conversion ADU with one detached ADU of 800 sq ft or less, and the multifamily limits on conversions and detached ADUs.
  • JADU and use conditions — owner occupancy for a JADU (and where state law overrides Union City's broader rule), the deed restriction, the 30-day minimum rental, separate sale, historic homes and new utility connections.
  • Where state law prevails — when Union City's text is stricter than California ADU law, the validator applies state law and says so in the finding.

Any ADU or JADU project in Union City that touches these rules is in scope, not only the scenarios pictured here. Not checked: building, fire and structural codes, impact and connection fees, objective design standards and other zoning beyond what is listed, hazard zones, private covenants, and the accuracy of the facts the caller states (such as transit distance or historic status). The validator reflects the codes as of September 30, 2026; later changes are not applied.

The permit intake assistantTakes in the ADU project from the homeowner and says it is ready for the permit application.
Predictika validatorChecks every rule at once and returns the verdict, each finding, and the computed figures.

7 scenarios in 3 groups · each group runs from the agent’s first attempt to the outcome · click one to switch

What the agent proposes

The permit intake assistant says

Illustrative agent statement. The validator receives the structured request below.

Proposing agent: permit intake assistant (scripted)

Before sending, the agent must call Recorded run

Predictika validator


      

        
        
        
      

      
Waiting for the call.

      
    

  

  
  

    
Where a rules-based permit checklist gets this wrong
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Our assessment of what a typical rules-based permit checklist or form validator (one rule per field, each limit checked on its own) does with the same cases. It is a judgment about effort and reliability, not a claim that nothing can be built.

    
What the validator caughtA rules-based permit checklistPredictika
A state-law rule that overrides a stricter local ruleOnly with workarounds
The city asks for an owner on site for every JADU, so a checklist fails a JADU with its own bathroom and an absent owner, even though state law does not allow that requirement there, and someone has to remember the exception.		Both sets of rules are checked together; where Union City's text is stricter, the state-law result is applied and the finding says state law prevails.
Limits that depend on each otherOnly with care
Trimming the detached unit from 900 to 800 sq ft changes the unit-count result, and giving the JADU its own bathroom changes the owner-on-site result, but a checklist treats size, count and bathroom as unrelated fields.		Size, height, setbacks, unit count and the JADU conditions are in one request and re-evaluated together on every call.
Limits that change with the lot and the unit typeOnly with care
Single-family and multifamily lots, conversions, attached and detached units and JADUs each have different caps, and a multistory building raises the height limit, so the rule list multiplies.		The lot type, unit type and building type are fields of the request, and every cap is computed from them.
A condition that applies only in some casesOnly with care
The owner must live on the property only when a JADU shares a bathroom, and a historic listing needs review only for a conversion, so each condition needs a guard.		The condition and its trigger are in the same request and checked together.
Every problem returned in one answerOnly with workarounds
Form checks usually stop at the first failing field, so an applicant fixes one error and meets the next.		All findings come back together, whatever order the choices arrived in.

  

  

    
What this validator catches: findings from its test cases
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Every rule is checked on every call, in any order the choices arrive; one problem never hides another. Blocking findings stop the permit application; approval findings need a person to sign off; everything else is computed.

    
1A new attached or detached ADU must stay within the size limit for its type (1,000 sq ft attached, 1,200 detached; 500 for a JADU), and a conversion has no size limit but may add at most 150 sq ft.
2Height must be within the limit that applies: 16 feet for a detached ADU, more near major transit, with a matching roof pitch or on a multistory multifamily building, and 30 feet and two stories for an attached ADU.
3New floor area needs at least 4 feet of side and rear setback.
4The front setback follows the district unless the unit is 800 sq ft or less.
5A single-family lot allows one ADU and one JADU, or a conversion ADU plus one detached ADU of 800 sq ft or less and a JADU.
6A multifamily lot allows conversions of up to 25 percent of existing units (at least one) and up to 8 detached ADUs, never more than the number of existing units.
7A JADU must be inside the single-family home, may be at most 500 sq ft, and needs a deed restriction.
8Union City requires the owner to live on the property for every JADU; where state law does not allow that (a JADU with its own bathroom), state law prevails.
9The rental term must be at least 30 days.
10The ADU may not be sold separately from the main home, except a sale that qualifies under Government Code section 66341, which gets staff review.
11A home listed in the California Register of Historical Resources gets staff review.
12New separate utility connections for a conversion or JADU get staff review.
13The unit needs a separate entrance and address, and a required passageway, parking or sprinklers are not demanded beyond what the law allows.

  

  

    
Scenarios and results
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The recorded result of the validator for each scenario on this page: the request the AI agent sent, the verdict, and every finding, in the order they appear above.

    
1. Three units on one single-family lot: A package of three units on one single-family lot

    
The agent's request. Please pre-screen this project for the Navarro household on their single-family lot in Union City: a new two-bedroom detached ADU of 900 sq ft, 18 feet tall, with a 3-foot side setback and a 4-foot rear setback, plus a garage conversion ADU and a JADU that shares a bathroom with the main home. The JADU will be inside the house and the owner agrees to a deed restriction. The owner does not live on the property. The units will be rented for 14 days at a time. It is ready for the permit application.

    
Verdict: Blocked.

    
    
      
  • Height over the limit. The detached ADU is 18 feet tall; the most generous limit that applies here is 16 feet.
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  • Side setback too small. The side setback is 3 feet and the rear setback is 4 feet; new floor area needs at least 4 feet on the side and rear.
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  • JADU needs the owner on site. The JADU shares a bathroom with the main home, so the owner must live on the property (a government agency, land trust or housing organization is exempt).
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  • Rental term under 30 days. A 14-day rental term is under the 30-day minimum.
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  • Too many ADUs on the lot. There would be two ADUs on a single-family lot. Union City allows up to two ADUs only as one new unit alone, or one detached unit of 800 sq ft or less plus one conversion unit, with one JADU in addition. This combination fits neither.
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  • Pre-screen. 5 items appear to conflict with the rules. Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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2. Three units on one single-family lot: The agent resubmits after fixing the errors

    
The agent's request. Please pre-screen this project for the Navarro household on their single-family lot in Union City: a new two-bedroom detached ADU of 800 sq ft, 16 feet tall, with a 4-foot side setback and a 4-foot rear setback, plus a garage conversion ADU and a JADU that shares a bathroom with the main home. The JADU will be inside the house and the owner agrees to a deed restriction. The owner does not live on the property. The units will be rented for 14 days at a time. It is ready for the permit application.

    
Verdict: Blocked.

    
    
      
  • JADU needs the owner on site. The JADU shares a bathroom with the main home, so the owner must live on the property (a government agency, land trust or housing organization is exempt).
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  • Rental term under 30 days. A 14-day rental term is under the 30-day minimum.
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  • Pre-screen. 2 items appear to conflict with the rules. Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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3. Three units on one single-family lot: The agent resubmits after fixing the errors

    
The agent's request. Please pre-screen this project for the Navarro household on their single-family lot in Union City: a new two-bedroom detached ADU of 800 sq ft, 16 feet tall, with a 4-foot side setback and a 4-foot rear setback, plus a garage conversion ADU and a JADU with its own bathroom. The JADU will be inside the house and the owner agrees to a deed restriction. The owner does not live on the property. The units will be rented for 365 days at a time. It is ready for the permit application.

    
Verdict: Allowed.

    
    
      
  • State law prevails: JADU owner occupancy. Union City's text requires the owner to live on the property for every JADU. This JADU has its own bathroom, and state law does not allow owner occupancy to be required in that case, so state law governs and the missing owner occupancy does not appear to conflict.
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  • Pre-screen. Every item checked appears to meet California ADU law and Union City's ADU rules, so the project appears approvable by right (ministerial review). One item appears approvable only because state law prevails. Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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4. Detached ADUs on a multifamily lot: Nine detached ADUs at 20 feet on a 12-unit multistory building

    
The agent's request. Please pre-screen this project on a multifamily lot in Union City with 12 existing units in a multistory building: nine new detached ADUs of 600 sq ft each, 20 feet tall, not within half a mile of major transit. The side setback is 3 feet and the rear setback is 4 feet. It is ready for the permit application.

    
Verdict: Blocked.

    
    
      
  • Height over the limit. The ADUs are 20 feet tall; the most generous limit that applies here is 18 feet.
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  • Side setback too small. The side setback is 3 feet and the rear setback is 4 feet; new floor area needs at least 4 feet on the side and rear.
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  • Too many detached ADUs. Nine detached ADUs exceed the limit of 8 (up to 8, and no more than the number of existing units).
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  • Pre-screen. 3 items appear to conflict with the rules. Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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5. Detached ADUs on a multifamily lot: The agent resubmits after fixing the errors

    
The agent's request. Please pre-screen this project on a multifamily lot in Union City with 12 existing units in a multistory building: eight new detached ADUs of 600 sq ft each, 18 feet tall, not within half a mile of major transit. The side setback is 4 feet and the rear setback is 4 feet. It is ready for the permit application.

    
Verdict: Allowed.

    
    
      
  • Pre-screen. Every item checked appears to meet California ADU law and Union City's ADU rules, so the project appears approvable by right (ministerial review). Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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6. Garage conversion in a historic home: A garage conversion in a listed historic home

    
The agent's request. Please pre-screen a garage conversion ADU of 650 sq ft at a listed historic home on a single-family lot in Union City. The conversion adds 200 sq ft for access, the unit will be rented for 14 days at a time and sold separately from the main home, and it will have new separate utility connections. It is ready for the permit application.

    
Verdict: Blocked.

    
    
      
  • Added area over 150 sq ft. A conversion may expand by at most 150 sq ft; this one adds 200 sq ft, and the added area would be treated as new construction.
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  • Rental term under 30 days. A 14-day rental term is under the 30-day minimum.
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  • Separate sale not allowed. A separate sale of the unit from the main home is not allowed, except a sale that qualifies under Government Code section 66341.
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  • Listed historic home. The property is listed in the California Register of Historical Resources, so objective preservation standards apply to exterior changes. Staff review is needed.
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  • New utility connections. Separate new utility connections are planned. An agency generally cannot require them, and fee treatment is outside this pre-screen. Staff review is needed.
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  • Pre-screen. 3 items appear to conflict with the rules; 2 more need staff review. Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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7. Garage conversion in a historic home: The agent resubmits after fixing the errors

    
The agent's request. Please pre-screen a garage conversion ADU of 650 sq ft at a listed historic home on a single-family lot in Union City. The conversion adds 120 sq ft for access, the unit will be rented for 365 days at a time and kept together with the main home, and it will have new separate utility connections. It is ready for the permit application.

    
Verdict: Needs approval.

    
    
      
  • Listed historic home. The property is listed in the California Register of Historical Resources, so objective preservation standards apply to exterior changes. Staff review is needed.
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  • New utility connections. Separate new utility connections are planned. An agency generally cannot require them, and fee treatment is outside this pre-screen. Staff review is needed.
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  • Pre-screen. No item appears to conflict with the rules; 2 items need staff review. Pre-screen as of September 30, 2026, not a permit decision. Facts such as transit distance and historic status are taken as the caller states them and are not verified.
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Narration transcript
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The text of the narrated walkthrough, step by step.

    
    
      
  1. Welcome to a demo of Predictika's Validator. A permit intake assistant takes in a homeowner's accessory dwelling unit (ADU) project in Union City, California, and says it is ready for a building-permit application. Before it goes out, the assistant sends it to Predictika's validator, which checks it against California ADU law and the City of Union City's ADU rules together, applies state law where it overrides a stricter local rule, and reports every problem it finds in one pass.
    2. 
      
  2. I will start with the first request by the agent.
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  3. The agent says. Please pre-screen this project for the Navarro household on their single-family lot in Union City: a new two-bedroom detached ADU of 900 sq ft. The JADU will be inside the house and the owner agrees to a deed restriction. The rest of the request is on screen.
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  4. Before it goes out, the agent calls the validator.
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  5. Blocked, with five findings, all in one answer. The detached ADU is 18 feet tall; the most generous limit that applies here is 16 feet. The side setback is 3 feet and the rear setback is 4 feet; new floor area needs at least 4 feet on the side and rear. The JADU shares a bathroom with the main home, so the owner must live on the property (a government agency, land trust or housing organization is exempt). The other two are on screen.
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  6. The validator returned five blocking findings in one answer. A check that reads one field at a time would pass most of this; it shows only when the choices in the permit application are checked against each other.
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  7. What this shows: for limits that depend on each other, a rules-based permit checklist is error-prone for this.
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  8. Now the agent resubmits.
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  9. The corrected request. It changes the size of the detached unit to 800 sq ft, the height of the detached unit to 16 ft and the side setback to 4 ft.
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  10. It calls the validator again.
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  11. Still blocked, with two findings, all in one answer. The JADU shares a bathroom with the main home, so the owner must live on the property (a government agency, land trust or housing organization is exempt). A 14-day rental term is under the 30-day minimum.
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  12. Three findings cleared. Still blocking: JADU needs the owner on site and rental term under 30 days.
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  13. The agent resubmits once more.
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  14. The revised request. It changes the JADU bathroom to its own bathroom and the rental term to 365 days.
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  15. It calls the validator once more.
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  16. This time the validator clears it.
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  17. Both earlier findings are cleared. Union City's text requires the owner to live on the property for every JADU. This JADU has its own bathroom, and state law does not allow owner occupancy to be required in that case, so state law governs and the missing owner occupancy does not appear to conflict.
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  18. Five problems caught in one call, fixed in two passes, and a clean permit application. That is the value of Predictika's validator: catching mistakes before the application goes to the permit counter. Now you can try the other scenarios yourself.
    19.