California ADU rules · Solano County
Can I Build an ADU in Fairfield?
Yes — you can build an ADU in Fairfield. California's statewide ADU law requires every city, including Fairfield, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
Local rule1 detached ADU and 1 JADU, or 1 ADU total
Local code clarifies either 1 detached ADU and 1 JADU, or 1 ADU total; state law preempts if more permissive.
Units on a multifamily lot
Local ruleConversions (>=1 or 25% of units) + up to 2 detached (or up to 8 detached, not to exceed number of existing units, per state law)
Local code references state law for detached ADUs; up to 2 detached locally, but up to 8 if state law applies.
Junior ADU (JADU)
Local ruleAllowed
Explicitly allowed; must be within existing/proposed single-family dwelling.
Size & height
Max detached ADU size
Local rule1,200 sq ft
Local maximum detached ADU size is 1,200 sq ft.
Max attached ADU size
Local rule50% of primary dwelling or 1,200 sq ft, whichever is less (minimum 850/1,000 per state law)
Local cap is 50% of primary or 1,200 sq ft, whichever is less; state minimums still apply.
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
Local rule500 sq ft
Local code sets 500 sq ft max for JADUs.
Max height
Local rule16 ft
16 ft standard; up to 25 ft if >50% of ADU is above a garage.
Setbacks
Side setback
Local rule4 ft
4 ft minimum for new construction ADUs.
Rear setback
Local rule4 ft
4 ft minimum for new construction ADUs.
Front setback
Local ruleMust comply with front yard setback of base zoning district
Front setback per base zone; cannot preclude state-mandated ADU.
Separation from main house
Local rule5 ft
Detached ADUs must be at least 5 ft from primary dwelling.
Parking
Parking required
Local ruleNone
No additional parking required for ADUs or JADUs.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
Local ruleNot required
No replacement parking required when converting garage/carport/covered parking.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
Local ruleOnly for a JADU
No owner-occupancy for ADUs; JADUs require owner-occupancy in JADU or primary dwelling.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
Local ruleBuilding permit, Planning ADU Permit (unless exempt under state law)
Planning ADU Permit required unless ADU is exempt under state law.
Fairfield-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Fire sprinklers
ADU must have fire sprinklers if required for the primary residence.
Historic property standards
ADUs/JADUs on historic properties must substantially comply with Secretary of the Interior standards.
Fairfield sets a 1,200 sq ft local cap for detached ADUs, requires a 5 ft separation from the primary dwelling, and mandates no additional or replacement parking for ADUs or JADUs. JADUs require owner-occupancy, and ADUs on historic properties must comply with federal standards.
Frequently asked questions
Can I build an ADU in Fairfield?
Yes. California's statewide ADU law requires Fairfield to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in Fairfield?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in Fairfield?
Side and rear setbacks are limited to 4 ft. Must comply with front yard setback of base zoning district.
Is parking required for an ADU in Fairfield?
None. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in Fairfield?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in Fairfield?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Fairfield Zoning Code § 25.50
- Fairfield Zoning Code § 25.50(D)(1)
- Fairfield Zoning Code § 25.50(D)(1); Gov. Code § 66323
- Fairfield Zoning Code § 25.50(E)(2)(b)
- Fairfield Zoning Code § 25.50(D)(2)(a)(ii)
- Fairfield Zoning Code § 25.50(D)(2)(a)(i)
- Fairfield Zoning Code § 25.50(D)(2)(a)(iii)
- Fairfield Zoning Code § 25.50(D)(2)(b)(ii)
- Fairfield Zoning Code § 25.50(D)(2)(b)(iii)
- Fairfield Zoning Code § 25.50(C)(4)
- Fairfield Zoning Code § 25.50(E)(2); Gov. Code § 66333(b)
- Fairfield Zoning Code § 25.50(B)(1)-(3), (F)
- Fairfield Zoning Code § 25.50(B)(5)
- Fairfield Zoning Code § 25.50(C)(5)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated 2026-06-25. This is an AI-assisted summary of Fairfield's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with Fairfield Planning before relying on it.
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