Los Altos Hills – ADU Regulations


All properties zoned in the R-A (Residential Agricultural) District with an existing single-family house are eligible to build an ADU.

Number of units

Lots zoned for single family use that have an existing dwelling are permitted to add 1 ADU and 1 Jr. ADU (JADU).

Building size

Maximum square footage is determined by your lot size, zoning and ADU type:

  • 500 sq. ft. for a Jr. ADU (JADU); if an on-site parking space is provided, a JADU can be up to 650 sq. ft.
  • Every property is eligible for an 800 sq. ft. ADU, even if it has reached the maximum floor area ratio for the lot
  • 850 sq. ft. for a 1 bedroom ADU
  • 1,000 sq. ft. for a 2+ bedroom ADU
  • If an ADU provides for 30 ft. side and rear yard setbacks and an additional parking space, an ADU may be up to 1,200 sq. ft.

Building height

Detached ADUs can reach a maximum height of 16 feet (one-story). Attached ADUs can reach the same height as the main structure, assuming they comply with municipal code (including daylight plane).

If a detached ADU provides side and rear setbacks of 30 ft. and an additional on-site parking space, the maximum building height can be increased to one-story and 19 ft.


Minimum setbacks of 4 feet from the side and rear lot lines, as well as 6 feet from any existing structures are required for detached ADUs. Front setbacks of 30 ft. are required.


One on-site parking space is required for accessory dwelling unit as follows:

  • The parking space may be covered or uncovered and shall be at least ten 10 ft. wide by 20 ft. feet deep
  • The space may be provided as tandem parking on a driveway or located in a setback area, unless specific findings are made by the planning director that parking in a setback area or as tandem is not feasible based upon specific site or regional topographical or fire and life safety conditions
  • The parking space shall not encroach into a required fire truck turnaround or obstruct the driveway access to the primary dwelling

No additional parking is required for JADUs or for conversion or replacement of an existing garage or carport. ADUs are exempt from the parking requirement if they are within 0.5 mi. of public transportation or a car share vehicle.


Owner occupancy is not a requirement for permitting an ADU from January 1, 2020 until January 1, 2025. This is a great opportunity for rental property owners to increase their yields in a cost-effective way.


While long-term rentals are permitted for ADUs, homeowners may be required to sign a deed restriction preventing short-term rentals (e.g. Airbnb for less than 30 days).