California ADU rules · Marin County
Can I Build an ADU in Larkspur?
Yes — you can build an ADU in Larkspur. California's statewide ADU law requires every city, including Larkspur, 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 (new), 1 conversion ADU, 1 JADU; max 2 ADUs + 1 JADU + primary (4 dwellings total)
Allows up to 2 ADUs (1 detached new, 1 conversion) plus 1 JADU on a single-family lot, not to exceed 4 dwellings total.
Units on a multifamily lot
Local ruleConversions: up to 25% of existing units; Detached: up to 2 (proposed multifamily) or up to 8 (existing multifamily), not to exceed number of existing units
Detached ADUs capped at 2 for proposed multifamily, 8 for existing multifamily, and total ADUs cannot exceed number of existing units.
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
Detached ADUs: 800 sqft by-right; up to 850 (studio/1-bed), 1000 (2-bed), or 1200/50% of primary (3+ beds), but not less than 800.
Max attached ADU size
Local ruleLesser of 1,200 sqft or 50% of primary dwelling (not less than 800 sqft for 3+ bedrooms)
Attached ADUs capped at 1,200 sqft or 50% of primary, whichever is less; 800 sqft minimum for 3+ bedrooms.
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
Local rule16 ft
Detached: 16 ft standard, 18 ft near transit/multifamily, up to 20 ft for roof pitch; attached: up to 25 ft or height of primary.
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
CA state lawNo front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
Local ruleUp to 1 space
1 off-street space per ADU; multiple exemptions apply.
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 garage/carport is converted or demolished for ADU/JADU.
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
30 days for completeness, 60 days for ministerial approval/denial after complete application.
Owner-occupancy
Local ruleOnly for a JADU
Owner-occupancy required for JADUs only; not required for ADUs.
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, Certificate of occupancy
Both building permit and certificate of occupancy required for all ADUs/JADUs.
Larkspur-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Very High Fire Hazard Severity Zone (VHFHSZ)
No additional fire sprinklers required for ADUs unless required for the primary dwelling.
Historic Districts/Properties
ADUs on historic properties or in historic districts require a professional report and must comply with Secretary of the Interior’s Standards.
Larkspur allows up to 2 ADUs plus 1 JADU on single-family lots, with nuanced caps for multifamily properties. Detached ADUs may exceed 800 sqft up to 1,200 sqft or 50% of the primary dwelling, and historic/fire zone rules apply.
Frequently asked questions
Can I build an ADU in Larkspur?
Yes. California's statewide ADU law requires Larkspur 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 Larkspur?
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 Larkspur?
Side and rear setbacks are limited to 4 ft. No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone.
Is parking required for an ADU in Larkspur?
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 Larkspur?
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 Larkspur?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Larkspur Municipal Code Chapter 18.23 (Ordinance 1096, effective Feb 4, 2026)
- LMC §18.23.050, §18.23.060(A)
- LMC §18.23.050(B), §18.23.060(F)
- LMC §18.23.060(F)(2)(c)
- LMC §18.23.060(G), (H)
- LMC §18.23.060(I)
- LMC §18.23.060(I)(5)
- LMC §18.23.040, §18.23.070(A)
- LMC §18.23.070(A)
- LMC §18.23.080
- LMC §18.23.060(P)
- LMC §18.23.060(J)
- 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 Larkspur'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 Larkspur Planning before relying on it.
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