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Los Altos Hills ADU Zoning And Building Standards

Los Altos Hills has specific zoning and building standards for ADUs that ensure the units blend harmoniously with the surrounding environment. These standards cover various aspects, including unit size, placement, and design features, ensuring that the new constructions maintain the aesthetic and functional integrity of the community. Understanding these guidelines is essential for a smooth approval process and to avoid costly mistakes.

DevArt8 Construction specializes in navigating these regulations, ensuring your ADU meets all local zoning and building standards. Our expertise and attention to detail will help you avoid common pitfalls and streamline the approval process. We provide comprehensive support, from site assessment to securing necessary permits, ensuring your project stays on track and within budget.

Los Altos Hills ADU Zoning and Building Standards

Property Requirements

Property requirements in Los Altos Hills for ADUs are designed to ensure that each unit is a beneficial addition to the community. These requirements address lot size, existing structures, and other critical factors that influence the feasibility of your ADU project. Compliance with these requirements is crucial to obtain approval from local authorities and ensure the longevity and functionality of your ADU.

Building Size

The size of your ADU is regulated to ensure it remains subordinate to the main dwelling and fits within the character of the neighborhood. These regulations vary based on the type of lot and existing structures. Adhering to these size constraints helps maintain neighborhood harmony and avoids potential conflicts with neighbors and local authorities.

  • Single-Family Zoned Lots:

Single-family zoned lots in Los Altos Hills are typically large, offering ample space for an ADU. The regulations for these lots are designed to ensure that ADUs are proportional to the main dwelling and do not disrupt the neighborhood’s character. This allows for seamless integration of the ADU, providing additional living space without compromising the aesthetic appeal of the area.

  • Duplex Family Zoned Lots:

For duplex family zoned lots, the regulations allow for the construction of ADUs in a manner that complements the existing structures. These lots can accommodate both attached and detached ADUs, providing flexibility in design and usage. This flexibility ensures that homeowners can choose the best option to suit their needs while adhering to zoning requirements.

  • Multi-Family Zoned Lots :

Multi-family zoned lots have specific regulations that allow for the inclusion of multiple ADUs. These regulations ensure that each unit is well-integrated into the overall property layout. This helps in maximizing the use of available space while maintaining a balanced and aesthetically pleasing environment.

  • Attached ADUs:

Attached ADUs must be integrated with the main structure, maintaining a cohesive architectural style. This ensures that the new unit blends seamlessly with the existing home, preserving the overall aesthetic of the property.

  • Detached ADUs:

Detached ADUs are standalone structures that provide additional living space while maintaining privacy and independence from the main dwelling. These units offer versatility and can serve as guest houses, rental units, or private retreats.


Los Altos Hills requires owner-occupancy for properties with ADUs, ensuring that either the main dwelling or the ADU is occupied by the property owner. This regulation helps maintain the community’s residential character and ensures proper property management. It also provides a sense of accountability and ensures that the property is well-maintained.

Number Of Units Allowed

The number of ADUs allowed on a property in Los Altos Hills varies based on zoning and lot size. Typically, single-family lots can accommodate one ADU, while multi-family lots may allow more, depending on specific zoning regulations. This regulation ensures a balanced density and prevents overcrowding, maintaining the town’s serene environment.

Los Altos Hills Building Height

The height of ADUs in Los Altos Hills is regulated to ensure they do not overshadow neighboring properties and maintain the area’s aesthetic appeal. Height restrictions vary based on the type of property and specific zoning guidelines.

  • Single-family: For single-family properties, ADUs are generally limited to a maximum height that ensures they remain secondary to the main dwelling. This helps preserve the visual integrity of the neighborhood and prevents the ADU from becoming a dominant feature.
  • Duplex family: Duplex family properties have height regulations that allow for a slightly higher ADU, accommodating the existing multi-family nature of the property. This ensures that the ADU is in harmony with the surrounding structures while providing adequate living space.
  • Multi-family: Multi-family properties can have taller ADUs, provided they comply with specific zoning regulations that ensure harmony with the surrounding structures. These regulations help maintain a balanced skyline and avoid overwhelming the existing buildings.

Los Altos Hills Building Size

The building size for ADUs in Los Altos Hills is carefully regulated to ensure that the units remain subordinate to the main dwelling and blend seamlessly with the neighborhood. These regulations help maintain the community’s aesthetic and functional balance.

  • Single-Family Freedom: Single-family properties enjoy significant freedom in ADU size, provided they comply with maximum size limits relative to the lot and main dwelling. This allows homeowners to create spacious and functional ADUs without compromising the overall property layout.
  • Duplex house: Duplex properties have specific size limits for ADUs that ensure they remain in proportion to the existing structures. This helps maintain a balanced appearance and prevents the ADU from overshadowing the main dwellings.
  • Multi-Family Mix: Multi-family properties can accommodate larger ADUs, subject to zoning regulations that maintain balance within the property layout. This flexibility allows for the creation of multiple living spaces while ensuring each unit is functional and aesthetically pleasing.

Fire Safety Regulations

Fire safety regulations for ADUs in Los Altos Hills are stringent, ensuring that each unit is equipped with necessary safety features like smoke detectors, fire extinguishers, and proper egress windows to protect occupants. These regulations are crucial for the safety and well-being of all residents and must be strictly adhered to during construction and occupancy.


Parking requirements for ADUs ensure that there is adequate space for residents without causing congestion. Typically, ADUs must provide at least one parking space, though some exemptions apply for properties near public transit. These requirements help maintain the neighborhood’s convenience and accessibility.

Utility Connections

Utility connections for ADUs must be properly planned and executed to ensure seamless integration with the main dwelling’s systems. This includes water, sewer, electricity, and gas connections, all of which must meet local code requirements. Proper utility connections are essential for the functionality and sustainability of the ADU.


Setbacks are crucial in Los Altos Hills to maintain space between structures and property lines. ADUs must adhere to specific setback requirements, which vary based on the type of property and location within the lot. These requirements help ensure privacy, light, and ventilation for both the ADU and neighboring properties.

Zoning Regulations

Zoning regulations in Los Altos Hills dictate where ADUs can be built and the specific requirements they must meet. These regulations ensure that ADUs are a beneficial addition to the community and maintain the town’s character.

Los Altos Hills ADU Zoning Regulations

Single Family

Single-family zones allow for ADUs that complement the primary residence, adhering to specific size and placement regulations. These guidelines ensure that the new units do not disrupt the neighborhood’s aesthetic or functional harmony.

Duplex Family

Duplex family zones have regulations that accommodate ADUs while maintaining the balance and character of the neighborhood. These regulations provide flexibility for homeowners while ensuring that the additional units are well-integrated.


Multi-family zones allow for multiple ADUs, with specific regulations ensuring they integrate well with existing structures and provide adequate living space. These guidelines help maximize the use of available space while maintaining a balanced and aesthetically pleasing environment.

RF Zone Minimum Lot Area In Los Altos Hills

In Los Altos Hills, 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 zoning designations help preserve the town’s open and serene character while allowing for diverse property uses.

  • RF-20: The RF-20 zone requires a minimum lot size that allows for comfortable single-family living with space for an ADU. This zoning designation ensures that properties maintain a balance between built structures and open space.
  • RF-30: RF-30 zoning offers larger lot sizes, accommodating more substantial ADUs and additional amenities. This provides flexibility for homeowners to create spacious and functional living environments.
  • RF-40: RF-40 zoning provides the largest lot sizes, ideal for expansive ADUs and luxury property features. These properties can accommodate a variety of additional structures and amenities, making them perfect for large families or those seeking more space.

Room Specifications

When designing your ADU, specific room specifications ensure functionality and comfort. The following table provides an overview of essential room requirements. These guidelines help ensure that each room is designed to meet the needs of future occupants, providing a comfortable and functional living environment.

Los Altos Hills ADU Room Specifications

Room TypeSpecifications
Bathroom1. Minimum of 1 full bathroom
2. Exhaust fan
3. Water-efficient fixtures
4. Adequate lighting
5. GFCI outlets
Kitchen1. Minimum of 1 kitchen area
2. Energy-efficient appliances
3. Ample countertop space
4. Storage cabinets
5. Proper ventilation
Sleeping Areas1. Minimum of 1 sleeping area
2. Egress windows
3. Smoke detectors
4. Adequate closet space
5. Comfortable living area
Storage1. Dedicated storage area
2. Built-in shelving
3. Lockable storage units
4. Easily accessible
5. Weatherproof construction

Los Altos Hills Requirements

Los Altos Hills has specific requirements for ADUs that ensure each unit is a valuable addition to the property while maintaining the community’s standards. These requirements include compliance with local building codes, zoning regulations, and environmental considerations.

Detached ADU Los Altos Hills: Detached ADUs must comply with size, setback, and height regulations. These units provide additional living space separate from the main dwelling, ideal for privacy and independence. Detached ADUs offer flexibility in design and usage, making them a popular choice for homeowners.

Attached ADU Los Altos Hills: Attached ADUs need to integrate with the existing structure, maintaining architectural cohesion and meeting specific building code requirements. These units provide additional living space while remaining connected to the main dwelling, offering convenience and accessibility.

JADU Los Altos Hills: Junior Accessory Dwelling Units (JADUs) are smaller ADUs that utilize existing space within the main dwelling, such as converting a bedroom into a separate living unit. These units are a cost-effective solution for adding living space without the need for extensive construction.

Rental Requirements

Rental requirements for ADUs ensure that tenants are reliable and the property is well-maintained. These requirements include various checks and documentation to ensure that the ADU remains a safe and habitable living space.

  • Proof of Income: Tenants must provide proof of income to ensure they can meet rental payments. This typically includes recent pay stubs, tax returns, or employment verification letters.
  • Credit Score: A minimum credit score is required to assess the financial responsibility of tenants. This helps landlords determine the likelihood of timely rent payments and overall financial stability.
  • Rental History: A positive rental history helps ensure tenants have a record of maintaining properties well. Landlords may request references from previous landlords to verify this information.
  • Application Fee: An application fee covers the cost of processing rental applications. This fee is typically non-refundable and may vary based on the landlord’s requirements.
  • Security Deposit: A security deposit protects against potential damage to the property. This deposit is usually equivalent to one or two months’ rent and is refundable at the end of the lease term, provided the property is in good condition.
  • Proof of Renter’s Insurance: Tenants must provide proof of renter’s insurance to cover personal belongings and potential liability. This insurance helps protect both the tenant and the property owner in case of accidents or damage.
  • Pet Policy: The pet policy outlines any restrictions or requirements for tenants with pets. This may include additional deposits, pet rent, or breed and size restrictions.
  • Smoking Policy: The smoking policy defines whether smoking is allowed in the unit and any associated restrictions. This helps maintain a clean and healthy living environment for all tenants.

Development Standards For Los Altos Hills ADU

Development standards for ADUs in Los Altos Hills ensure that each unit is well-designed, functional, and compliant with local regulations. The following table provides an overview:

ADU TypesDevelopment Standards Specifications
Single-family1. Maximum size of 1,200 sq ft
2. Maximum height of 16 feet
3. Minimum setbacks of 4 feet
4. One parking space required
5. Owner-occupancy required
Duplex1. Maximum size of 1,200 sq ft
2. Maximum height of 18 feet
3. Minimum setbacks of 4 feet
4. One parking space per unit
5. Owner-occupancy required
Multi-family1. Maximum size of 1,200 sq ft
2. Maximum height of 18 feet
3. Minimum setbacks of 4 feet
4. One parking space per unit
5. Owner-occupancy required
Junior ADUs (JADUs)1. Maximum size of 500 sq ft
2. Must be within existing structure
3. Separate entrance required
4. Kitchen and bathroom facilities
5. Owner-occupancy required

Los Altos Hills Property Designations For ADU

Certain property designations in Los Altos Hills impact the feasibility and design of ADUs. These include flood zones, geohazard zones, and easements. Understanding these designations is crucial for ensuring the safety and compliance of your ADU project.

  • Flood Zones: Properties in flood zones must adhere to additional regulations to mitigate flood risks, including elevated construction and specific materials. These measures help protect the ADU and its occupants from potential flood damage.
  • Geohazard Zones: Geohazard zones require additional geotechnical assessments to ensure the safety and stability of the ADU. These assessments help identify and mitigate risks associated with landslides, earthquakes, and other geological hazards.
  • Easements: Easements must be respected in ADU design, ensuring that access and utility rights are maintained. This includes providing necessary clearance for utility lines, driveways, and other essential infrastructure.

ADU Permit Requirements And Fees

Permitting is a crucial part of the ADU development process in Los Altos Hills, ensuring compliance with all local regulations. The permit process involves several steps and associated fees, which must be accounted for in your project planning.

Los Altos Hills ADU Permit Requirements and Fees

  • Building Permit: A building permit is required for all ADUs, covering the structural aspects of the project. This permit ensures that the construction meets local building codes and standards.
  • Electrical Permit: An electrical permit ensures that all electrical work meets safety standards. This includes wiring, outlets, lighting, and other electrical installations.
  • Plumbing Permit: A plumbing permit is necessary for any plumbing installations or modifications. This includes water supply lines, drainage systems, and gas lines.
  • Other Permits: Other permits may include mechanical, grading, and demolition permits, depending on the scope of the project. These permits ensure that all aspects of the construction comply with local regulations.

Design Your Dream ADU Today!

Designing your dream ADU in Los Altos Hills is a collaborative process that blends your vision with practical considerations. DevArt8 Construction is here to help you navigate the complexities, ensuring your ADU is a perfect fit for your property and lifestyle. Contact us today to get started on your ADU project, and let us bring your vision to life with precision and excellence. Our team of experts will work closely with you throughout the entire process, from initial concept to final completion, ensuring your satisfaction and the success of your ADU project.


Yes, but specific setbacks and design considerations apply. Contact the Los Altos Hills 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.