Introduction
The regulations governing ADUs in Los Altos ensure streamlined and efficient development processes, balancing urban growth with community aesthetics. These rules facilitate homeowners in enhancing property value while contributing to housing solutions. ‘ADU Specialist Bay Area’ offers expert guidance through each step, ensuring compliance and smooth project execution.
Essential ADU Rules for Los Altos
What you can build
Maximum size
ADUs up to 1,200 sq ft are permitted.
Side / rear setbacks
Minimum setbacks are 4 feet.
Two stories
Two-story ADUs are allowed under specific conditions.
Building separation
A minimum separation of 10 feet from other structures is required.
Permitting timeline
Standard
Typically takes 60-90 days.
Coastal
Varies based on environmental review processes.
Zoning Regulations in Los Altos
Zoning regulations in Los Altos are designed to support ADU development while maintaining neighborhood character. Specific zoning requirements must be met.
ADU Size Limitations
| Lot Size | Single-Family (Maximum Floor Area Allowed) | Duplex and Multi-Family (Maximum Floor Area Allowed) |
| Under 7000 | 700 sq ft | Not permitted |
| 7000 - 9999 | 800 sq ft | 1 ADU + 400 sq ft per existing unit (up to 1000 sq ft max) |
| 10000 - 12999 | 900 sq ft | 1 ADU + 450 sq ft per existing unit (up to 1000 sq ft max) |
| 13000 - 19999 | 1000 sq ft | 1 ADU + 500 sq ft per existing unit (up to 1000 sq ft max) |
| 20000+ | 1000 sq ft | 1 ADU + 550 sq ft per existing unit (up to 1000 sq ft max) |
ADU Height Limitations
ADUs in Los Altos must not exceed 16 feet in height unless otherwise specified by zoning laws.
Building Coverage
The total coverage of all structures must not exceed 40% of the lot area.
Location
| Property Type | Location Requirement |
| Single-Family Homes | Attached ADUs: Must be within primary structure |
| Detached ADUs: Must be in the rear half of the lot | |
| Junior ADUs (JADUs): Must be within the existing residence | |
| Duplex and Multifamily | Attached ADUs: Can be within existing units or attached |
| Detached ADUs: Must be in the rear half of the lot |
Exterior details
ADUs should match the architectural style and color scheme of the main house, ensuring visual harmony.
Parking
One parking space per ADU is required, which can be in tandem configuration on the driveway.
Setbacks and buffer zones
ADUs must maintain a minimum setback of 4 feet from the side and rear property lines to ensure privacy and space.
Minimum Lot Area
| Lot Size | Minimum Lot Area for ADU | Description |
| Under 7000 | ADUs not permitted | Lots under 7000 sq ft are not eligible for ADUs |
| 7000 - 9999 | 7000 sq ft | Must have at least 7000 sq ft |
| 10000 - 12999 | 10000 sq ft | Must have at least 10000 sq ft |
| 13000 - 19999 | 13000 sq ft | Must have at least 13000 sq ft |
| 20000+ | No minimum lot area requirement | Any size lot is eligible for an ADU |
Connection for utilities
ADUs must have independent utility connections for water, sewer, and electricity to ensure functional autonomy.
Fire safety
All ADUs must comply with local fire codes, including smoke detectors, fire sprinklers, and clear access routes.
Room specifications
- Sleeping Areas: Must include proper egress windows and a minimum ceiling height of 7 feet.
- Kitchen: Requires a sink, refrigerator, stove, and adequate counter space.
- Bathroom: Must have a toilet, sink, and shower or bathtub.
- Storage: Adequate storage must be provided, including closets and cabinetry.
Short-term Rentals and Home Occupations Regulations
Short-term rentals are not permitted in ADUs, and home occupations must adhere to specific zoning regulations.
Building Codes
ADUs must comply with California Building Code standards, ensuring safety and structural integrity.
Los Altos ADU Permit Guidelines
| Permit Type | Description | Estimated Fee |
| Building Permit | Required for ADU construction. | $2500 - $5000 |
| Electrical Permit | Required for electrical systems. | $400 - $700 |
| Plumbing Permit | Required for plumbing installations. | $400 - $700 |
| Mechanical Permit | Required for HVAC systems. | $400 - $700 |
| Grading Permit | Needed for site preparation. | $300 - $500 |
| Site Development Permit | Required for site development works. | $300 - $500 |
| Zoning Permit | Required for zoning compliance. | $200 - $400 |
Property requirements
Properties must meet specific requirements to be eligible for ADUs, including compliance with zoning and building codes.
Parking
One parking space is required per ADU, which can be accommodated on the driveway in a tandem arrangement.
Front setbacks
A minimum front setback of 20 feet is required to maintain the street frontage aesthetics.
Side and rear setbacks
ADUs must maintain a minimum side setback of 4 feet and a rear setback of 4 feet.
Open space and rear yards
A minimum of 30% of the lot must remain as open space, ensuring sufficient greenery and recreational areas.
Properties that qualify
To determine your property’s eligibility for ADU development, contact the Los Altos Planning Department.
- Verify that your property is within Los Altos’ jurisdiction.
- Check the specific residential zones that permit ADUs. Common zones in Los Altos include R-1, R-2, and R-M.
- Other General Plan designations that permit ADUs:
- Residential Mixed-Use (RMU): Encourages a blend of residential and commercial uses.
- Transit-Oriented Development (TOD): Focuses on higher density near transit hubs.
- Specific Plan areas: May have unique requirements that support ADU development.
Development standards
Single-family
- Attached: Must comply with the primary residence’s design and cannot exceed 50% of the main home’s floor area.
- Detached: Must be located in the rear yard and not exceed 1,200 sq ft.
Duplex properties
- Attached: Can be built within existing structures or attached to the primary building.
- Detached: Should be in the rear half of the property, adhering to size limits.
Multifamily properties
- Attached: Can utilize existing non-livable spaces, such as basements or garages.
- Detached: Must be located in designated areas of the property, ensuring adequate space for each unit.
Junior ADUs (JADUs)
JADUs must be created within the primary residence and limited to 500 sq ft, with a separate entrance and kitchenette.
Property designations
- Flood Zones: Properties in flood zones must comply with additional regulations to ensure safety and flood resilience.
- Geohazard Zones: ADU construction in geohazard zones requires a geotechnical report to assess risks and mitigation measures.
- Historic Designation: ADUs on historically designated properties must preserve the historical integrity and comply with specific guidelines.
- Easements: Any existing easements must be respected, and ADUs cannot encroach upon these designated areas.
Summary
Creating an ADU in Los Altos involves navigating a variety of regulations and standards to ensure safety, functionality, and aesthetic harmony. ‘ADU Specialist Bay Area’ can help streamline the process, providing expert advice and handling all aspects of compliance and construction.
FAQ
In Los Altos, ADUs can be up to 1,200 sq ft, ensuring sufficient living space while complying with local regulations.
The minimum setback requirements are 4 feet from the side and rear property lines to ensure privacy and space.
Yes, two-story ADUs are permitted under specific conditions, allowing for more flexible designs.
There must be at least 10 feet of separation between the ADU and other structures on the property.
The standard permitting process typically takes 60-90 days, depending on the project specifics.
Yes, coastal areas may require additional environmental reviews, which can affect the timeline.
Zoning regulations in Los Altos support ADU development while maintaining neighborhood character, requiring compliance with specific zoning laws.
ADUs must not exceed 16 feet in height unless otherwise specified by zoning laws.
The total coverage of all structures on the lot must not exceed 40% of the lot area.
ADUs must be within the rear half of the lot for detached units and can be within the primary structure for attached units.
ADUs should match the architectural style and color scheme of the main house to ensure visual harmony.
Yes, one parking space per ADU is required, which can be in tandem configuration on the driveway.
ADUs are not permitted on lots under 7,000 sq ft, with varying requirements for larger lots.
Yes, ADUs must have independent utility connections for water, sewer, and electricity to ensure functional autonomy.
ADUs must comply with local fire codes, including smoke detectors, fire sprinklers, and clear access routes.
Specifications include proper egress windows, adequate kitchen and bathroom facilities, and sufficient storage space.
Short-term rentals are not permitted in ADUs in Los Altos, promoting long-term housing solutions.
ADUs must comply with California Building Code standards, ensuring safety and structural integrity.
Required permits include building, electrical, plumbing, mechanical, grading, site development, and zoning permits.
Yes, properties must meet zoning and building code requirements to be eligible for ADUs.
One parking space per ADU is required, which can be accommodated on the driveway in a tandem arrangement.
A minimum front setback of 20 feet is required to maintain the street frontage aesthetics.
ADUs must maintain a minimum side setback of 4 feet and a rear setback of 4 feet.
A minimum of 30% of the lot must remain as open space, ensuring sufficient greenery and recreational areas.
