The City of Los Altos permits ADUs across most residential zones. Los Altos follows both state and local ADU laws, allowing most single-family homes to build one detached ADU and one Junior ADU (JADU) per lot. Multi-family properties may be eligible for multiple ADUs, depending on site conditions.

Los Altos aligns with California’s broader ADU legislation but has its own requirements for height, setbacks, and design review.

• Detached ADU: A standalone unit in the backyard
• Attached ADU: A unit attached to the main home
• Conversion ADU: A unit created by converting existing space in the main home or an accessory structure (like a garage or basement) into a separate living unit
• Junior ADU (JADU): An ADU of 500 square feet or less in size with an efficiency kitchen, with or without sanitation facilities, is called a junior accessory dwelling unit (JADU) and is permitted within a single-family home.

• Maximum Size:
  
  • Detached: The maximum size of a detached accessory dwelling unit that is a studio or with one (1) bedroom is eight hundred and fifty (850) square feet and the maximum size of an accessory dwelling unit with more than one (1) bedroom is one thousand (1,000) square feet
  • Attached: The maximum size of an attached accessory dwelling unit is one thousand (1,000) square feet or fifty (50) percent of the primary dwelling’s living area, whichever is less, provided that at least 800 square feet is allowed
    
• Setbacks:
  
  • Minimum 4 ft from side and rear property lines for all ADU types (Detached, Attached, Conversion, and JADU)
    
• Height Limits:
  
  • Typically The greater of 16 feet or the height of the underlying zoning district whichever is greater.
    
• Parking Requirements:
  
  • Additional parking is not required if the ADU is:
    
    • Converted from an existing area of the residence or an accessory structure
    •  Converted or demolished garage, carport, or parking structure to accommodate the ADU
    • Located within half a mile of public transit (bus stop or train station)
    • In a historic district or architecturally/historically significant area
    • On-street parking permits required in the area but not available to the ADU occupant

To build an ADU in Los Altos, the following approvals and submittals are typically required:

• Building permit application submission
• Site plan showing property lines, existing structures, proposed ADU, setbacks, utilities, and driveways
• Architectural drawings (floor plans, elevations, roof plan, cross-sections)
• Structural calculations and engineering, if applicable
• Fire flow verification letter from water provider
• Tree removal or protection permit (if applicable)
• Administrative design review approval for detached accessory structures over 120 sq ft
• Permit submission through the City of Los Altos Building Division
  

Homeowners should also review Los Altos’ current fee schedule, utility connection requirements, and fire code compliance.

The review times for ADU permits in Los Altos can vary based on project complexity and city workload. Typically, the review process takes between 6 to 12 weeks. However, projects requiring corrections or additional documentation may experience longer review periods. Engaging professionals familiar with Los Altos’ ADU process can help streamline approval and potentially reduce delays.

Most residential zones are eligible for ADUs, including R-1 zones. There are no minimum lot sizes for ADUs in most areas of Los Altos. Some hillside or environmentally sensitive zones may have special restrictions.

For the most current and complete information, refer directly to the City of Los Altos.