California ADU rules · San Mateo County
Can I Build an ADU in Brisbane?
Yes — you can build an ADU in Brisbane. California's statewide ADU law requires every city, including Brisbane, 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 ADU (detached or attached) + 1 JADU; max 4 total units if urban lot split or two-unit development (SB 9) applies
SB 9 overlay may further limit total units to 4 on a single lot
Units on a multifamily lot
Local ruleConversions: up to 25% of existing units (minimum 1); Detached: up to 8, but not to exceed number of existing main units; JADUs not allowed
Detached ADUs capped at number of main units; JADUs prohibited on multifamily lots
Junior ADU (JADU)
Local ruleAllowed
JADUs allowed only on single-family lots
Size & height
Max detached ADU size
CA state law1,200 sq ft
Statewide default cap for detached new-construction ADUs in the absence of a compliant local ADU ordinance. The unconditional by-right floor a city must always allow is 800 sq ft (see Guaranteed minimum size); a city with a compliant ordinance may set its own ceiling.
Max attached ADU size
CA state law50% of the primary dwelling, but ≥850 sq ft (≥1,000 sq ft for 2+ bedrooms) is always allowed
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
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
CA state lawUp to 1 space
At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.
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 conversions
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
Owner-occupancy required only for JADUs
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
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
Brisbane-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)
ADUs/JADUs must comply with all applicable building, health, and fire codes; sprinklers required only if main dwelling requires them
Brisbane caps detached ADUs at 800 sq ft and prohibits JADUs on multifamily lots. Detached ADU height is 16 ft, or 18 ft for multistory multifamily or near transit. No replacement parking is required for garage conversions.
Frequently asked questions
Can I build an ADU in Brisbane?
Yes. California's statewide ADU law requires Brisbane 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 Brisbane?
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 Brisbane?
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 Brisbane?
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 Brisbane?
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 Brisbane?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- Brisbane Municipal Code Chapter 17.43 (Ord. No. 700, last amended 10-2-25)
- §17.43.070(B) & Table; §17.43.060(D)(2)
- §17.43.050(B)(1)-(2); §17.43.070(B)
- §17.43.060(E)(1)
- §17.43.040(M)(1); §17.43.060(J)(1)
- §17.43.060(H)
- §17.43.040(P)(1); §17.43.060(L)(1)
- 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 § 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 Brisbane'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 Brisbane Planning before relying on it.
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