San Mateo County

Brisbane ADU rules

Research summary of local ADU rules on file for Brisbane in San Mateo County. Not a determination for a specific lot.

Last checked October 26, 2026.

City or county ADU page

Brisbane rules on file

Local rules recorded in this project for this jurisdiction. Where a city figure on file is stricter than the state baseline on file, both are shown.

Local ADU rules
Brisbane's ADU rules are in Municipal Code Chapter 17.43, amended by Ordinance No. 700, adopted October 2, 2025 and in effect 30 days after adoption. ADU and JADU building permit applications are reviewed ministerially and acted on within 60 days of a complete application. If the application also creates a new home, the City acts on it after the new home's permit, and the ADU cannot be occupied before the new home.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.030 (Section 8); Section 18, accessed 2026-10-25.

ADU types under state law (state-exempt units)
On a single-family lot, any mix of: an ADU inside the proposed or existing home or an existing accessory structure (an accessory structure may grow up to 150 sq ft for entry and exit), one new detached ADU up to 800 sq ft, and a JADU. On multifamily lots: ADUs in non-livable space such as storage rooms, attics, basements or garages (at least one, up to 25% of existing units), plus detached ADUs (up to 8 with existing multifamily, not more than the number of existing units; up to 2 with proposed multifamily). These units do not count toward lot coverage or floor area and are exempt from parking and landscaping rules, and they may be placed in the front setback.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), §§ 17.43.040, 17.43.050, 17.43.070 (Sections 9, 10, 15), accessed 2026-10-25.

Where ADUs are allowed
ADUs are allowed in the R-1, R-2, R-3, R-BA, NCRO-2, SCRO-1, PAOZ-1, PAOZ-2 and PD districts on lots with an existing or proposed single-family home, multifamily building or dwelling group. There is no minimum lot size, and ADUs do not count toward the lot's density.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.040 (Zoning Districts, Density, Lot Size), accessed 2026-10-25.

Maximum size
ADUs that are not state-exempt units may be up to 1,000 sq ft of floor area. A new detached state-exempt ADU may be up to 800 sq ft; converted state-exempt ADUs have no size cap.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.040 (Unit Size); § 17.43.070(C), accessed 2026-10-25.

Side and rear setbacks
At least 4 ft from side lot lines (or the zone's side setback if less) and 4 ft from the rear lot line. No setback is needed to convert existing legal living area, a garage or an accessory structure, or to rebuild one in the same place and size.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.040 (Setbacks), accessed 2026-10-25.

Height of attached ADUs
An attached ADU may be up to two stories and must meet the height limit of the zone.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.040 (Height), accessed 2026-10-25.

Parking
No parking is needed for an ADU in the R-1, R-2, R-3, NCRO-2, SCRO-1, PAOZ-1 or PAOZ-2 districts, for any state-exempt ADU, or for a JADU. When a garage, carport or parking space is removed or converted for an ADU, the spaces do not have to be replaced.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.34.020 (Section 6); § 17.43.040 (Parking), accessed 2026-10-25.

Facilities and entry
Each ADU needs a full kitchen and a full bathroom. An attached ADU needs its own exterior entry, separate from the main home's entrance; an interior door is allowed only off a common living area of the main home.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.040 (Required Facilities, Unit Access), accessed 2026-10-25.

Fees and utilities
No impact fees for a JADU or an ADU under 750 sq ft; ADUs of 750 sq ft or more pay impact fees in proportion to the main home's size. An ADU is not a new residential use for City water and sewer connection fees, and separate water, sewer or power connections are not required.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.030 (fees); § 17.43.040 (Utilities), accessed 2026-10-25.

Fire sprinklers
Fire sprinklers are not needed in an ADU or JADU unless the main home needs them.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.040 (Compliance with Codes); § 17.43.060 (Compliance with Codes), accessed 2026-10-25.

Junior ADUs
One JADU per lot with a single-family home, up to 500 sq ft inside the existing walls of the home (an attached garage counts as part of the home), with at least an efficiency kitchen. The bathroom may be shared with the main home or separate. A JADU needs its own exterior entry and no off-street parking. A recorded declaration of restrictions bars selling the JADU separately and renting it for less than 30 days.
Source: City of Brisbane Ordinance No. 700 (ADU and JADU amendments to BMC Chapters 15.10, 17.02, 17.12, 17.16, 17.32, 17.34 and 17.43; Municode ordinance bank), § 17.43.060 (Section 11), accessed 2026-10-25.

California state rules on file

The statewide baseline recorded from state law and the HCD ADU Handbook.

Detached size cap described in state law
1,200 sq ft. Recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Side and rear setback cap for a new ADU
4 ft. Recorded in this rules file from Government Code section 66314, which describes a cap on side and rear setbacks for a new ADU.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Setback for a conversion of an existing structure
No additional setback, as recorded in this rules file from Government Code section 66314 for a conversion of an existing structure.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Minimum lot size
A city may not impose a minimum lot size for an ADU, as recorded in this rules file from Government Code section 66314.
Source: California Government Code section 66314, 66314, accessed 2026-10-16.

Minimum unit the handbook says cities must allow
At least an 800 sq ft ADU with 4 ft side and rear setbacks. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(3).
Source: HCD ADU Handbook, 66321(b)(3); handbook updated March 2026, accessed 2026-10-16.

Detached height described in the handbook
16 ft, or 18 ft or 20 ft in some cases. The HCD ADU Handbook (updated March 2026) describes this under section 66321(b)(4).
Source: HCD ADU Handbook, 66321(b)(4); handbook updated March 2026, accessed 2026-10-16.

Permit decision deadline
60 days. Recorded in this rules file from Government Code section 66317(a)(3): the permitting agency must decide on (approve or deny) a completed ADU application within 60 days when an existing single-family or multifamily dwelling is on the lot. Section 66317(a)(1) says the application is considered ministerially, without discretionary review or a hearing.
Source: California Government Code section 66317, 66317(a)(1), (a)(3), accessed 2026-10-17.

Owner-occupancy requirement
None. Recorded in this rules file from Government Code section 66315: a local agency may not impose an owner-occupancy requirement on an ADU. It may require that the property be used for rentals of terms 30 days or longer. The HCD ADU Handbook (updated March 2026) describes the same rule.
Source: California Government Code section 66315, 66315; HCD ADU Handbook updated March 2026, accessed 2026-10-17.

Parking near public transit
No parking standards within one-half mile walking distance of public transit. Recorded in this rules file from Government Code section 66322(a)(1). Section 66322(a) lists several other cases where parking standards may not be imposed.
Source: California Government Code section 66322, 66322(a), accessed 2026-10-17.

Ministerial categories
The HCD ADU Handbook (updated March 2026) states that Government Code section 66323 sets four ministerial categories. This rules file does not restate those four categories.
Source: HCD ADU Handbook, 66323; handbook updated March 2026, accessed 2026-10-16.

Fire Hazard Severity Zones
If your lot is in a Fire Hazard Severity Zone, the CAL FIRE Office of the State Fire Marshal says in Information Bulletin 25-004 (issued March 3, 2025): “Fire Hazard Severity Zones (FHSZs) should not restrict the development of Accessory Dwelling Units (ADUs). However, additional building standards may be necessary, including but not limited to California Fire Code Chapter 49 and California Building Code Chapter 7A.” State ADU law does not itself bar an ADU there. A city or county may still apply its building code, including wildfire-resistant construction (Gov. Code 66314(d)(8)); require side and rear setbacks “sufficient for fire and safety” for a unit converted under 66323(a)(1); and decline parking in setbacks on specific fire and life safety findings (66314(d)(10)(B)). It may also consider public safety when it designates where ADUs may be permitted (66314(a)). Sprinklers can't be required in an ADU or JADU if the primary residence doesn't need them (66314(d)(12), 66323(d)). Some cities and counties still apply their own fire-zone limits. Where this summary has one, it is listed with the local rules. This summary does not look up your lot. Check the CAL FIRE Fire Hazard Severity Zone map viewer linked from the State Fire Marshal's Fire Hazard Severity Zones page: https://experience.arcgis.com/experience/5065c998b4b0462f9ec3c6c226c610a9
Source: CAL FIRE Office of the State Fire Marshal Information Bulletin 25-004, page 4, issued March 3, 2025; Gov. Code 66314, 66323, accessed 2026-10-20.

State baseline on the directory → · State ADU rules on the homepage →

Can I build an ADU in Brisbane?

State law sets a baseline for ADUs in Brisbane, and the local standards on file are listed on this page. Whether a specific lot can add an ADU depends on zoning, utilities, and other site facts this page does not measure. Confirm with the City of Brisbane Community Development Department (Planning), or run a free address summary.

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