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Foster City ADU Zoning And Building Standards

Foster City, renowned for its beautiful waterfronts and well-planned neighborhoods, has become an attractive location for homeowners interested in building Accessory Dwelling Units (ADUs). The city offers detailed guidelines and regulations to ensure that your ADU project aligns with local standards, providing a smooth process from the initial planning stages to the final construction.

How We Can Help

We are dedicated to guiding you through each phase of your ADU project in Foster City. From navigating zoning regulations to obtaining necessary permits, our experienced team ensures your ADU meets all city requirements. Our comprehensive support makes the process stress-free and efficient, ensuring your vision becomes a reality without unnecessary complications.

Foster City ADU Zoning and Building Standards

Property Requirements

In Foster City, specific property requirements must be met to build an ADU. These regulations ensure that the ADU is compatible with the main dwelling and the neighborhood, maintaining the area’s overall aesthetic and functionality.

Building Size

The size of your ADU in Foster City will depend on your property’s zoning and specific lot size. These regulations are designed to preserve the character and integrity of residential areas while allowing for additional housing options that blend seamlessly into the community.

  • Single-Family Zoned Lots:

For single-family zoned lots, ADUs must comply with size and setback regulations. These requirements are intended to preserve the character of the neighborhood while providing homeowners with the flexibility to add valuable living space.

  • Duplex Family Zoned Lots:

Duplex family zoned lots in Foster City can accommodate ADUs under certain conditions. These regulations ensure that the additional unit fits harmoniously within the existing property layout, providing a balance between density and livability.

  • Multi-Family Zoned Lots :

Multi-family zoned lots have specific guidelines to accommodate multiple ADUs. These regulations ensure that the development is cohesive and maintains the aesthetic integrity of the community, providing a diverse range of housing options.

  • Attached ADUs:

Attached ADUs must share at least one wall with the main dwelling and follow specific size restrictions. This integration ensures that the new unit blends seamlessly with the existing structure, providing additional living space without significantly altering the property’s appearance.

  • Detached ADUs:

Detached ADUs are separate structures on the same lot as the main dwelling. They must adhere to specific size and setback requirements to maintain neighborhood harmony and ensure that the additional unit complements the main residence.


Foster City requires that either the main dwelling or the ADU be owner-occupied. This regulation helps ensure that properties are well-maintained and that the community remains vibrant and engaged. Owner-occupancy requirements foster a sense of responsibility and investment in the neighborhood’s well-being.

Number Of Units Allowed

The number of ADUs allowed on a property in Foster City depends on the zoning designation. Typically, single-family lots allow one ADU, while multi-family lots may permit more, depending on the specific zoning regulations and property size. This flexibility allows for diverse housing solutions while maintaining the area’s character.

Foster City Building Height

Building height regulations in Foster City vary depending on the type of dwelling and zoning designation. These rules ensure that new constructions blend well with existing structures and do not disrupt the visual harmony of the neighborhood.

  • Single-family: For single-family homes, ADUs must comply with height restrictions that ensure they do not overshadow neighboring properties or alter the neighborhood’s character. These height limits are designed to maintain a cohesive streetscape and prevent any one structure from dominating the visual landscape.
  • Duplex family: Duplex properties in Foster City have specific height restrictions for ADUs. These regulations ensure that the additional units are compatible with the existing buildings and the surrounding area, maintaining a balanced and harmonious environment.
  • Multi-family: Multi-family properties have more flexible height regulations, allowing for taller ADUs that can accommodate more residents while maintaining aesthetic harmony. These rules provide opportunities for increased density and diverse housing options without compromising the community’s visual appeal.

Foster City Building Size

Building size regulations in Foster City ensure that ADUs are proportionate to the lot size and existing structures. These rules help preserve the residential area’s overall look and feel, ensuring that new constructions complement the existing environment.

  • Single-Family Freedom: Single-family homes in Foster City enjoy a degree of freedom in ADU size, provided they meet the overall lot coverage and setback requirements. This flexibility allows homeowners to add substantial living space while maintaining the neighborhood’s character.
  • Duplex house: Duplex properties must ensure that ADUs do not exceed the allowable size limits, maintaining balance and proportion with the main dwelling. These size restrictions help preserve the aesthetic and functional harmony of the property and the surrounding area.
  • Multi-Family Mix: Multi-family properties can accommodate larger ADUs, allowing for diverse housing options while adhering to specific size regulations. These guidelines ensure that the additional units fit well within the property’s overall design and do not overwhelm the existing structures.

Fire Safety Regulations

Foster City mandates strict fire safety regulations for ADUs. These include requirements for fire-resistant materials, smoke detectors, and clear access for emergency services. These safety measures ensure that all ADUs provide a secure living environment for residents.


Parking requirements for ADUs in Foster City vary by zoning designation but generally include provisions for off-street parking to minimize neighborhood congestion. These regulations help ensure that the addition of an ADU does not negatively impact the availability of parking for other residents.

Utility Connections

ADUs in Foster City must have independent utility connections for water, electricity, and sewage. This ensures that they function as separate living units and comply with all health and safety standards. Proper utility connections are essential for the ADU’s functionality and the well-being of its occupants.


Setback requirements in Foster City ensure that ADUs maintain adequate distance from property lines. These rules preserve privacy, reduce the impact on neighboring properties, and ensure that the new units fit harmoniously within the existing layout.

Zoning Regulations

Foster City’s zoning regulations for ADUs ensure that new units are compatible with the existing residential environment. These rules maintain community standards and ensure that new developments enhance the neighborhood rather than detract from it.

Foster City ADU Zoning Regulations

Single Family

Single-family zoning regulations allow for one ADU per property, provided it meets size, height, and setback requirements. These guidelines ensure that the additional unit complements the main dwelling and the overall neighborhood.

Duplex Family

Duplex zoning regulations in Foster City accommodate ADUs while ensuring they do not disrupt the balance and aesthetic of the existing duplex properties. These rules help maintain the character and livability of duplex neighborhoods.


Multi-family zoning regulations allow for multiple ADUs, with specific guidelines to ensure that the development remains cohesive and in harmony with the neighborhood. These regulations provide flexibility while maintaining the area’s visual and functional integrity.

RF Zone Minimum Lot Area In Foster City

In Foster City, RF Zone minimum lot sizes range from spacious single-family homes (RF-20) to sprawling estate properties (RF-40), ensuring ample space for your ADU and lifestyle. These lot size requirements ensure that each property can comfortably accommodate an ADU while maintaining the neighborhood’s character.

  • RF-20: RF-20 zones require a minimum lot size that accommodates single-family homes with ADUs, ensuring enough space for comfortable living and additional amenities. These lot sizes provide a balance between density and spaciousness.
  • RF-30: RF-30 zones provide larger lot sizes for single-family homes, allowing for more substantial ADUs and additional features. These larger lots offer more flexibility in ADU design and placement.
  • RF-40: RF-40 zones offer the largest lot sizes, ideal for expansive single-family homes and larger ADUs. These lots provide ample space and privacy, making them suitable for more extensive ADU projects.

Room Specifications Table

ADU room specifications ensure that each living space is functional, comfortable, and compliant with building standards. These guidelines ensure that all rooms meet the necessary requirements for safety, comfort, and usability.

Foster City ADU Room Specifications

Bathroom– Size: 60 sq. ft.
– Ventilation: Exhaust fan
– Fixtures: Low-flow toilet and shower
– Flooring: Water-resistant tiles
– Accessibility: Grab bars
Kitchen– Size: 100 sq. ft.
– Countertops: Durable material
– Appliances: Energy-efficient
– Ventilation: Range hood
– Storage: Ample cabinetry
Sleeping Areas– Size: 120 sq. ft.
– Windows: Egress compliant
– Closets: Built-in
– Flooring: Carpeting or hardwood
– Lighting: Overhead and task
Storage– Size: 50 sq. ft.
– Shelving: Adjustable
– Accessibility: Easy access
– Security: Lockable
– Ventilation: Adequate airflow

Foster City Requirements

Foster City has specific requirements for ADUs to ensure they are safe, functional, and compatible with the main dwelling and surrounding neighborhood. These regulations cover various aspects of ADU construction and use, ensuring high-quality living spaces.

Detached ADU Foster City: Detached ADUs in Foster City must meet specific size, setback, and height regulations. These rules ensure that the additional unit complements the main dwelling and does not disrupt the neighborhood’s harmony.

Attached ADU Foster City: Attached ADUs must share at least one wall with the main dwelling and adhere to size and design guidelines. These requirements ensure that the ADU integrates seamlessly with the existing structure, providing additional living space without significantly altering the property’s appearance.

JADU Foster City: Junior Accessory Dwelling Units (JADUs) are smaller, converted spaces within the main dwelling. They must meet specific size and functionality requirements, providing a cost-effective housing solution while utilizing existing space efficiently.

Rental Requirements

Foster City has rental requirements for ADUs to ensure that tenants are qualified and that properties are well-maintained. These regulations help maintain the quality and safety of rental units, benefiting both landlords and tenants.

  • Proof of income: Tenants must provide proof of income to ensure they can afford the rent. This typically includes recent pay stubs, bank statements, or tax returns, demonstrating financial stability.
  • Credit score: A good credit score is required to demonstrate financial responsibility and reliability as a tenant. Landlords use credit scores to assess the risk of renting to potential tenants.
  • Rental history: Prospective tenants must provide a rental history to show they have a track record of being good renters. This includes references from previous landlords and rental agreements.
  • Application fee: An application fee is required to cover the costs of processing the rental application and conducting background checks. This fee helps landlords screen potential tenants effectively.
  • Security deposit: A security deposit is required to cover any potential damage to the property and ensure the tenant fulfils the lease terms. The deposit provides financial protection for landlords.
  • Proof of renter’s insurance: Tenants must provide proof of renter’s insurance to cover their personal belongings and liability in case of accidents. This insurance helps protect both the tenant and the property owner.
  • Pet policy: The pet policy outlines whether pets are allowed in the ADU and any associated fees or restrictions. This policy helps manage potential damage and nuisance issues related to pets.
  • Smoking policy: The smoking policy specifies whether smoking is allowed in the ADU. This regulation helps maintain a clean and healthy living environment for all residents.

Development Standards For Foster City ADU

Development standards for ADUs in Foster City ensure that new units are safe, functional, and aesthetically pleasing. These guidelines cover various aspects of ADU construction and use, ensuring high-quality living spaces.

ADU TypesDevelopment Standards Specifications
Single-family– Max size: 850 sq. ft.
– Setback: 5 ft.
– Height limit: 16 ft.
– Owner occupancy required
– Utility connections required
Duplex– Max size: 950 sq. ft.
– Setback: 5 ft.
– Height limit: 16 ft.
– Owner occupancy required
– Parking: 1 space required
Multi-family– Max size: 1,200 sq. ft.
– Setback: 10 ft.
– Height limit: 18 ft.
– Owner occupancy required
– Utility connections required
Junior ADUs (JADUs)– Max size: 600 sq. ft.
– Setback: 4 ft.
– Height limit: 16 ft.
– Owner occupancy required
– Parking: 1 space required

Foster City Property Designations For ADU

Property designations in Foster City determine where ADUs can be built and ensure that they are safe and compatible with the main dwelling. These designations help maintain the quality and safety of residential areas.

  • Flood zones: Properties in flood zones must meet specific building standards to ensure the safety and resilience of ADUs during floods. These standards include elevation requirements and waterproofing measures.
  • Geohazard zones: Geohazard zones require additional building precautions to protect ADUs from natural hazards like earthquakes and landslides. These precautions include foundation reinforcements and structural enhancements.
  • Easements: Easements must be respected when building ADUs, ensuring that access rights and utilities are not disrupted. These easements include utility lines, access paths, and shared spaces.

ADU Permit Requirements And Fees

Foster City requires various permits for ADU construction to ensure that new units meet all safety and building standards. These permits cover different aspects of the construction process.

Foster City ADU Permit Requirements and Fees

  • Building Permit: A building permit is required for the construction of an ADU, ensuring that the structure complies with local building codes. This permit covers the overall design and construction of the unit.
  • Electrical Permit: An electrical permit ensures that all electrical work in the ADU meets safety standards and is properly installed. This permit covers wiring, outlets, lighting, and other electrical components.
  • Plumbing Permit: A plumbing permit is necessary to ensure that all plumbing work in the ADU is up to code and safely installed. This permit covers pipes, fixtures, water heaters, and other plumbing elements.
  • Other Permits: Depending on the scope of the project, additional permits may be required for specific aspects of the ADU construction, such as roofing or landscaping. These permits ensure that all elements of the project meet safety and quality standards.

Design Your Dream ADU Today!

Ready to design your dream ADU in Foster City? Our team is here to help you every step of the way, ensuring your project meets all local regulations and exceeds your expectations. Contact us today to get started on your ADU journey! With our expertise and support, you can create a beautiful, functional, and compliant ADU that enhances your property and provides valuable living space.


Yes, but specific setbacks and design considerations apply. Contact the Woodside Planning Department for detailed guidance on navigating unique lot shapes.

Some lenders offer ADU loans, but traditional home loans can also be used for ADU construction, especially if they add value to your property.

Yes! The State of California offers various ADU incentive programs, including grants for low-income homeowners and developers. Research state and local programs to see if you qualify for financial assistance.

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