California ADU rules · San Mateo County
Can I Build an ADU in San Bruno?
Yes — you can build an ADU in San Bruno. California's statewide ADU law requires every city, including San Bruno, 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
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
Local ruleconversions (>=1 or 25% of units) + up to 8 detached (not to exceed number of existing units); up to 2 detached on lot with proposed multifamily
Detached ADUs on multifamily lots capped at number of existing units; only 2 detached allowed on lots with proposed (not existing) multifamily.
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
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
Local ruleSame as detached: 850 sq ft (studio/1-bed) or 1,000 sq ft (2+ bed) on lots <7,500 sq ft; 1,200 sq ft (2+ bed) on lots ≥7,500 sq ft
Attached ADUs subject to same size limits as detached.
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 rule0 ft
Detached: 16 ft (single-family/single-story multifamily), 18 ft (multi-story multifamily or within 1/2 mile of major transit), up to 25 ft for attached ADUs or ADUs over garage.
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
Local ruleNone required
No minimum separation required; must meet building/fire code.
Parking
Parking required
Local ruleUp to 1 space
1 per ADU unless exempt; exemptions per state and local code.
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
Local ruleOnly for a JADU
No owner-occupancy for ADUs; JADUs require owner to reside in primary or JADU.
Impact-fee waiver
Local ruleWaived under 1,200 sq ft
No impact fees for any ADU or JADU, regardless of size.
Permits required
Local ruleBuilding permit, JADU deed restriction
JADUs require a recorded deed restriction in addition to building permit.
San Bruno-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Fire code compliance
ADUs must comply with all applicable building and fire codes; sprinklers not required if not required for primary dwelling.
Airport noise overlay
ADUs in 65 CNEL or higher must meet Aircraft Noise Insulation Program standards.
San Bruno sets ADU size maximums based on lot size, with stricter caps for smaller lots and no impact fees for any ADU or JADU. Multifamily detached ADUs are capped at the number of existing units, and JADUs require owner occupancy.
Frequently asked questions
Can I build an ADU in San Bruno?
Yes. California's statewide ADU law requires San Bruno 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 San Bruno?
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 San Bruno?
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 San Bruno?
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 San Bruno?
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 San Bruno?
Owner-occupancy: only for a jadu. ADUs under 1,200 sq ft are also exempt from impact fees.
Sources
- San Bruno Municipal Code Chapter 12.90, as amended by Ord. 1947 (4/9/2024), Ord. 1958 (1/28/2025), Ord. 1965 (8/26/2025)
- SBMC §12.90.030(C)(1)
- SBMC §12.90.050(E)(4)
- SBMC §12.90.050(E)(7)
- SBMC §12.90.050(E)(2)(b)
- SBMC §12.90.050(E)(9)
- SBMC §12.90.050(E)(9)(d)
- SBMC §12.90.060(B)
- SBMC §12.90.080(C)
- SBMC §12.90.040, §12.90.060(B)
- SBMC §12.90.050(B), (D)
- SBMC §12.90.050(D)
- 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 § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
Last updated 2026-06-25. This is an AI-assisted summary of San Bruno'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 San Bruno Planning before relying on it.
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