California ADU rules · Humboldt County
Can I Build an ADU in Eureka?
Yes — you can build an ADU in Eureka. California's statewide ADU law requires every city, including Eureka, 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 ruleUp to 2 ADUs (attached or detached) + 1 JADU; in RE and R1 zones, total dwellings (primary + ADUs + JADU) cannot exceed 4
Allows more than state baseline; zone cap applies in RE/R1.
Units on a multifamily lot
Local ruleUp to 8 detached ADUs (not exceeding number of existing primary units) + internal ADUs (up to 25% of existing units, or at least 1); on lots with proposed multifamily, max 2 attached or detached ADUs
Detached ADUs capped at 8 or number of existing units, whichever is less.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,200 sq ft
Local cap applies unless state exemption (Gov. Code § 66323(a)(1), (3), (4)).
Max attached ADU size
Local rule1,200 sq ft cap (same as detached); state exemption applies for conversions
Local cap unless state exemption.
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
CA state law500 sq ft
Max height
CA state law16 ft
16 ft baseline; cities must allow 18 ft within ½ mi of a major transit stop or where the primary dwelling is two-story, and 20 ft on a lot with a multistory multifamily building.
Setbacks
Side setback
CA state law4 ft
A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.
Rear setback
CA state law4 ft
Front setback
Local ruleNo minimum front setback for new ADUs ≤800 sq ft with 4-ft side/rear setbacks, or for ADUs qualifying under state law
Front setback waived for certain ADUs.
Separation from main house
Local ruleNone required
No minimum separation required.
Parking
Parking required
Local ruleNone
No on-site 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 if garage is converted.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
Local rule45 days
Shorter than state default; applies to lots with existing dwellings.
Owner-occupancy
Local ruleOnly for a JADU
Owner-occupancy required for JADUs only.
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 ruleZoning clearance, Building permit
Both zoning clearance and building permit required.
Eureka-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Historic properties (EMC Ch. 157)
ADUs on historic properties must comply with historic preservation rules, except detached ADUs not between historic building and street, interior conversions, and some attached ADUs are exempt from historic review.
Eureka allows up to 2 ADUs plus 1 JADU on single-family lots, with a local 1,200 sq ft cap for both attached and detached ADUs (unless exempt under state law). No parking is required for ADUs or JADUs, and historic property rules may apply.
Frequently asked questions
Can I build an ADU in Eureka?
Yes. California's statewide ADU law requires Eureka 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 Eureka?
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 Eureka?
Side and rear setbacks are limited to 4 ft. No minimum front setback for new ADUs ≤800 sq ft with 4-ft side/rear setbacks, or for ADUs qualifying under state law.
Is parking required for an ADU in Eureka?
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 Eureka?
A complete application must be acted on within 45 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 Eureka?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Eureka Municipal Code § 155.316 (Accessory Dwelling Units), last amended Ord. 951-C.S. (10-17-23)
- EMC § 155.316.040(A)
- EMC § 155.316.040(B)
- EMC § 155.316.060(D)(2)
- EMC § 155.316.060(F)
- EMC § 155.316.060(C)(1)
- EMC § 155.316.060(G)
- EMC § 155.316.060(G)(2)
- EMC § 155.316.020(B)
- EMC § 155.316.060(J)
- EMC § 155.316.020(A)
- EMC § 155.316.060(H)
- 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 § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- 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 Eureka'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 Eureka Planning before relying on it.
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