San Bruno ADU Zoning and Building Standards

San Bruno, California, is ideal for adding an Accessory Dwelling Unit (ADU) to your property. Recent amendments to California’s ADU law make this investment progressive and beneficial for property value. However, understanding San Bruno’s specific regulations for ADU construction is crucial. Local ordinances ensure that new ADU constructions align with community standards, promoting development and neighborhood harmony.

San Bruno ADU Zoning and Building Standards

Property Requirements

Building Size

  • Single Family Zoned Lots:

Building size for ADUs here is generally flexible, with no minimum lot size and a maximum size determined by your floor area ratio (FAR) and zoning district. The FAR is a ratio of your ADU’s floor area to the total lot area. It ensures your ADU doesn’t overwhelm the property.

  • Duplex Family Zoned Lots:

In duplex zones, you can build one detached ADU with a maximum size of 850 sq. ft. for a one-bedroom unit or 1,000 sq. ft. for a two-bedroom or more unit. Additionally, you can build multiple converted ADUs within existing non-livable spaces like garages or basements, up to 25% of the existing dwelling units.

  • Multi-Family Zoned Lots:

The rules get more specific. You can build up to two detached ADUs with the same maximum sizes as duplex zones. Additionally, you can create converted ADUs within existing structures, but the number depends on the type of ADU and the number of existing units on the property.


Owner-occupancy is only required for ADU permits on January 1, 2025, meaning you can build and rent out your ADU for maximum income without living on the property. Enjoy the flexibility to choose whether to occupy the main dwelling or the ADU or maximize rental potential!

Number of Units Allowed

In single-family lots, you can build one detached ADU and one Junior ADU (JADU) within an existing structure. One detached ADU is allowed for duplex lots, with additional JADUs depending on existing units. In multi-family lots, up to two detached ADUs and JADUs can be built within existing structures, depending on existing units.

San Bruno Building Height

  • Single-Family: ADUs here enjoy the most generous height allowance – a maximum of 16 feet. Whether you dream of a spacious two-story layout or a lofted studio, you have plenty of vertical freedom.
  • Duplex Family: Can still reach a respectable 16 feet, offering ample room for comfortable living spaces.
  • Multi-Family: Height is capped at 14 feet, but fear not, you can still create functional one- or even two-bedroom layouts within this limit.

San Bruno Building Size

  • Single-Family: There is no minimum lot size here, just a flexible maximum based on your Floor Area Ratio (FAR). Think of it as a ratio of your ADU’s size to your lot’s size. The higher your FAR, the bigger you can build!
  • Duplex Family: Play it safe with a maximum of 850 sq. ft. for a one-bedroom ADU or 1,000 sq. ft. for two bedrooms or more. Feeling creative? Convert existing spaces like garages into cozy ADUs, up to 25% of your dwelling size.
  • Multi-Family: Double the fun with up to two detached ADUs following the same size limits as duplex zones. Convert existing spaces, but the number of ADUs depends on the type and existing units on the property.

Fire Safety Regulations

All ADUs need interconnected smoke alarms on every level, including hallways outside bedrooms. Regular testing and maintenance are crucial. Sprinklers aren’t usually required for ADUs in San Bruno if they’re not mandatory in the primary residence. However, they’re highly recommended for extra protection.


Detached ADUs usually require one parking space unless exempted. Exemptions apply if you’re within ½ mile of public transit, existing structures, or historic districts. Attached ADUs and Junior ADUs typically don’t need dedicated parking, saving space and hassle.

Utility Connections

If possible, connecting your ADU to the existing utilities of your main dwelling is efficient and cost-effective. This applies to water, sewer, and gas lines. In some cases, separate meters might be required for your ADU, particularly for electricity. This allows for individual billing and usage tracking.


Detached ADUs require a minimum distance of 4 feet from side and rear property lines and 6 feet from existing structures. Front lot line setbacks should also be respected. Attached ADUs can share walls with the main structure. Junior ADUs have no strict setbacks but require enough space for fire safety.

Zoning Regulations

San Bruno ADU Zoning Regulations

Single Family

Lets you build your dream home with flexibility on lot size and generous maximum ADU size based on your Floor Area Ratio. There is no minimum lot size, just zoning rules and creative freedom to design your perfect haven!

Duplex Family

One detached ADU (up to 850 sq. ft. for one bed, 1,000 sq. ft. for two+) joins your existing home, with bonus converted ADUs possible in garages or basements. Think cozy guest havens or rental income potential!


Build up to two detached ADUs (same size limits as duplex zones) and potentially add converted ADUs within existing structures, depending on the number of existing units. Imagine a vibrant ADU community or maximizing rental potential – the possibilities are exciting!

RF Zone Minimum Lot Area in San Bruno

The minimum lot area for the RF zone in San Bruno varies depending on the specific lot location and zoning district within the RF zone. Here are some examples of minimum lot areas for different zoning districts within the RF zone:

  • R-1-20: Minimum lot area of 2,000 sq. ft. (single-family homes)
  • R-1-30: Minimum lot area of 3,000 sq. ft. (single-family homes)
  • R-2: Minimum lot area of 5,000 sq. ft. (single-family homes)

Room Specifications

Room TypeSpecifications
Bathroom– Shower or bathtub – Toilet

– Sink

– Exhaust fan

– Minimum floor area of 35 sq. ft. (excluding fixtures)

– Ceiling height of 7.5 ft. (min. clearance)

Kitchen– Sink with hot and cold water

– Refrigerator/freezer

– Countertop with space for food preparation – Stovetop or cooktop

– Exhaust fan

– Minimum floor area of 40 sq. ft. (excluding fixtures)

– Ceiling height of 7.5 ft. (min. clearance)

Sleeping Areas– Closet or built-in storage

– Window for natural light and ventilation

– Minimum floor area:

– Studio: 150 sq. ft.

– One-bedroom: 70 sq. ft.

– Two-bedroom: 70 sq. ft. per bedroom

– Ceiling height of 7 ft. (min. clearance)

Storage– Dedicated space for storing cleaning supplies, linens, etc.

– Can be in closets, cabinets, or built-in units

– Consider utilizing vertical space with wall shelves or hanging organizers

San Bruno Requirements

  • Detached ADU San Bruno: Standalone unit with private living space, ideal for guests, renters, or generating income. Requires separate permits and connections. Offers privacy and flexibility.
  • Attached ADU San Bruno: Seamlessly connect extra living space to your home, perfect for family members, home office, or additional bedrooms. Sharing utilities and permits with the main dwelling saves space and enhances connection.
  • JADU San Bruno: Compact and well-equipped spaces within existing structures, perfect for creating studios, gyms, or guest rooms. Simplified permitting requirements may apply. It is ideal for maximizing existing space without major construction.

Rental Requirements

  • Building Permit: Obtain a building permit specific to ADU construction from the San Bruno Planning Department. Costs vary depending on the size and complexity of your ADU but typically range from $1,000 to $5,000.
  • Business License: Apply for a business license from the San Bruno Finance Department if you plan to operate your ADU as a short-term rental (less than 30 days). The cost is usually around $100.
  • Tenant Screening: Implement a thorough tenant screening process to ensure responsible and compatible occupants for your ADU.
  • Lease Agreements: Have a clear and detailed lease agreement outlining rental terms, responsibilities, and maintenance procedures for you and your tenant.
  • Taxes and Insurance: Report rental income on your tax returns and consider obtaining landlord insurance for additional protection.

Development Standards for San Bruno ADU

ADU TypesDevelopment Standards Specifications
Single-family– No minimum lot size, maximum size based on Floor Area Ratio (FAR)

– One detached ADU + one JADU

Duplex– One detached ADU (850 sq. ft. for 1-bed, 1,000 sq. ft. for 2+)

– JADUs possible in existing structures (25% of existing dwelling units)

Multi-family– Up to two detached ADUs (same size limits as duplex)

– JADUs possible in existing structures (depending on number of existing units)

Junior ADUs (JADUs)– Must be within existing non-livable spaces (garages, basements)

– No specific size restrictions, but require sufficient space for fire safety

San Bruno Property Designations for ADU

  • Flood zones: San Bruno, nestled along the San Francisco Bay, is susceptible to flooding. The Federal Emergency Management Agency (FEMA) designated certain areas as flood zones, indicating varying degrees of flood risk. Building an ADU in a flood zone requires specific regulations and mitigation measures to ensure safety and compliance.
  • Geohazard zones: San Bruno also sits within a region with potential earthquakes and landslides. Geohazard zones are designated based on the likelihood of these events occurring. Building an ADU in a geohazard zone may require additional structural reinforcement and design considerations.
  • Easements: grants specific rights to use a portion of your property to another party, often for utilities, roads, or drainage purposes. Building an ADU within or near an easement might be restricted or require approval from the easement holder.

ADU Permit Requirements and Fees

Elegant ADU In San Bruno

  • Building Permit: The foundation permit for your ADU covers all construction aspects. Costs vary depending on size and complexity, typically from $1,000 to $5,000.
  • Electrical Permit: Ensures your ADU’s electrical system meets safety standards. Fees usually fall within $100-$300.
  • Plumbing Permit: Guarantees your ADU’s plumbing system adheres to codes. Expect costs around $100-$200.
  • Mechanical Permit: Covers heating, ventilation, and air conditioning (HVAC) systems. Fees are generally around $100-$200.
  • Plan Review Fees: Vary based on the complexity of your ADU plans but typically range from $500 to $1,500.

Design Your Dream ADU Today!

Discover the potential of designing your dream ADU in San Bruno! Our expert team will guide you through each step, ensuring your vision aligns with local regulations. Create a space that adds value to your property and enhances your lifestyle. Call us at +1-669-293-1126 to schedule a consultation and bring your ideal ADU to life!



Short-term rentals (less than 30 days) require a business license, but longer-term leases are fair game! Welcoming a remote worker to contribute to the local economy is a win-win situation.

No, ADUs in San Bruno are generally limited to residential use. Check the zoning regulations for your property to confirm permitted uses.

Yes, you must disclose any existing ADUs to potential buyers. This includes providing information about permits, inspections, and relevant rental agreements.