California ADU rules · San Joaquin County
Can I Build an ADU in Lathrop?
Yes — you can build an ADU in Lathrop. California's statewide ADU law requires every city, including Lathrop, 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 + 1 attached/conversion ADU + 1 JADU (total 4 units incl. primary)
Allows both a detached and an attached/conversion ADU plus a JADU on a single-family lot.
Units on a multifamily lot
Local ruleConversions: >=1 or up to 25% of units from non-livable space; Detached: up to 8, but not more than number of existing units; Proposed multifamily: up to 2 detached ADUs
Detached ADUs on multifamily lots capped at number of existing units; up to 2 detached ADUs for proposed multifamily.
Junior ADU (JADU)
Local ruleAllowed
JADUs allowed only within single-family dwellings, not multifamily.
Size & height
Max detached ADU size
Local rule1,200 sq ft
Local maximum matches state cap; not more restrictive.
Max attached ADU size
Local rule50% of primary, >=850 (>=1,000 for 2+ bedrooms)
Explicitly codifies state minimums and 50% rule.
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
Local rule4 ft
Street side setback is 10 ft; conversions may have no setback.
Rear setback
Local rule4 ft
Conversions may have no setback.
Front setback
Local ruleNo greater than required for primary residence
ADUs cannot be required to have a greater front setback than the primary.
Separation from main house
Local ruleNone required
No specific minimum; must comply with building code separation.
Parking
Parking required
Local ruleUp to 1 space
1 off-street space per ADU or per bedroom, whichever is less.
Transit parking exemption
Local ruleYes — no parking required near transit & for conversions
No parking required if within 1/2 mile of public transit or other state exemptions.
Garage-conversion replacement parking
Local ruleNot required
No replacement required for parking lost to ADU/JADU conversion or demolition.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
Local rule60 days
15 days for completeness check; 60 days for approval.
Owner-occupancy
Local ruleOnly for a JADU
No owner-occupancy for ADUs; JADU requires owner-occupancy only if sanitation is shared.
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
Must comply with all applicable building/fire codes.
Lathrop-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
Sprinklers required for ADU/JADU only if required for primary residence per California Building Code.
Historic district
Parking exemption applies if ADU is in a historic district.
Lathrop allows both a detached and an attached/conversion ADU plus a JADU on single-family lots, for up to four units total. Height limits and parking rules vary by ADU type and proximity to transit, and detached ADUs are capped at 1,200 sq ft.
Frequently asked questions
Can I build an ADU in Lathrop?
Yes. California's statewide ADU law requires Lathrop 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 Lathrop?
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 Lathrop?
Side and rear setbacks are limited to 4 ft. No greater than required for primary residence.
Is parking required for an ADU in Lathrop?
Up to 1 space. 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 Lathrop?
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 Lathrop?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Lathrop Municipal Code Chapter 17.80 (Ord. 23-449, 11/13/2023)
- § 17.80.020.C-D
- § 17.80.020.E
- § 17.80.020.C, § 17.80.030.A.2.a
- § 17.80.030.A.1.b
- § 17.80.030.A.1.a
- § 17.80.030.A.3.a
- § 17.80.030.A.3.c
- § 17.80.030.C.1
- § 17.80.030.D.1
- § 17.80.030.D.6
- § 17.80.050.B
- § 17.80.030.A.1.f, § 17.80.030.A.2.d
- § 17.80.040.B
- § 17.80.030.A.1.d, § 17.80.030.A.6
- § 17.80.030.D.2
- 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 § 66333 (junior ADUs)
- 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 Lathrop'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 Lathrop Planning before relying on it.
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