California ADU rules · San Mateo County
Can I Build an ADU in South San Francisco?
Yes — you can build an ADU in South San Francisco. California's statewide ADU law requires every city, including South San Francisco, 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 JADU + 1 conversion ADU (within existing space)
Allows both a detached ADU and a conversion ADU in addition to a JADU on a single-family lot.
Units on a multifamily lot
Local ruleup to 2 detached ADUs + conversions (>=1 or 25% of units)
Caps detached ADUs on multifamily lots at 2, not 8 as in state baseline.
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 rule1,000 sq ft
Detached ADU max: 850 sq ft (1 bedroom or less), 1,000 sq ft (more than 1 bedroom).
Max attached ADU size
Local rule50% of primary dwelling, or 850 (1 bedroom or less), or 1,000 (2+ bedrooms), whichever is greater
Allows attached ADU up to 50% of primary or state minimums, whichever is greater.
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
16 ft standard; 18 ft if within ½ mile of major transit or for multifamily/multi-story; attached ADUs up to 25 ft or primary dwelling height, whichever is less.
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
No more than 1 space per ADU or per bedroom, whichever is less; exemptions per state law.
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 for garage/carport conversion.
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
CA state lawOnly for a JADU
No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.
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, Demolition permit (if garage conversion)
Demolition permit required concurrently for garage conversion.
South San Francisco limits detached ADUs to 1,000 sq ft (more than 1 bedroom) and allows only 2 detached ADUs on multifamily lots. No replacement parking is required for garage conversions.
Frequently asked questions
Can I build an ADU in South San Francisco?
Yes. California's statewide ADU law requires South San Francisco 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 South San Francisco?
A detached ADU of at least 1,000 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 South San Francisco?
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 South San Francisco?
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 South San Francisco?
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 South San Francisco?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- South San Francisco Planning Code § 207.2 (State-Mandated ADU Program)
- SF Planning Code § 207.2(d)(1)-(4), (e)
- SF Planning Code § 207.2(d)(4), (e)
- SF Planning Code § 207.2(e)(6)
- SF Planning Code § 207.2(e)(5)
- SF Planning Code § 207.2(e)(9)
- SF Planning Code § 207.2(e)(8)
- 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 § 66315 (owner-occupancy)
- 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 South San Francisco'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 South San Francisco Planning before relying on it.
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