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Los Altos Hills, California: ADU Regulations

City or County:

Los Altos Hills, California

Date Updated:



R-A (only existing single-family homes)

Types of ADUs:

Attached, Detached, Junior
Note: New ADUs that provide on-site parking with rear and side setbacks of 30’ qualify for incentives in floor area and height.


Short-term rentals not allowed.


Detached: One story max

Lot Size:


Maximum ADU Floor Area:

Attached/Detached - Studio and One-Bedroom: 850 sq.ft.
Attached/Detached - Two-Bedroom: 1,000 sq.ft.
Attached/Detached - Incentives met for expansion: 1,200 sq.ft.
Junior: 500 sq.ft.
Junior - Incentives met for expansion: 650 sq.ft.
Note: Floor Area incentives all subject to MDA and MFA Lot coverage requirements

Lot Coverage:

Floor area up to 800 sq.ft. is exempt from a lot’s maximum development area (MDA) and maximum floor area (MFA). All floor area over 800 sq.ft. is counted


Min. 1 bedroom


No min/max


Require separate kitchen facilities (permanent range, counters, refrigerator, and sink).


Requires at least one full bathroom.

Note: Drainage and sewer connections should be assessed on a project by project basis.


1 parking space must be provided of 10'x20' and in setback or in tandem, unless the planning director finds it infeasible to abide by setback standards of zone based on site, topographical, or fire and life safety conditions. Parking space cannot encroach into a required fire truck turnaround or obstruct the driveway access to the primary dwelling. State parking exceptions apply (public transit, historic district, no permits for ADU occupants, car share, attached/conversion/junior) as well as when garage, carport of covered parking structure is demolished in conjunction with construction of/conversion to ADU.


Front of 40’, Side/Rear of 4’

Note: Fire Department regulations should be assessed on a project by project basis.


Attached: subject to primary residence
Detached: 16’
Detached - Incentives met for expansion: 19’ .


If separate from primary dwelling, ADU shall not be sited in a visually prominent location and shall respect the visual and acoustic privacy of primary dwellings on contiguous lots. Additionally, views of prominent scenic features by primary dwellings on contiguous lots to be preserved.

Rear Yard Coverage:



Secondary dwelling to be subordinate to and architecturally consistent with primary dwelling, and Attached will be “constructed so that the entire structure appears to be one dwelling”. All exterior lighting should be shrouded and/or downward facing. Exterior finish colors for new ADUs need light reflectivity value of 50 or less, and roof materials need LRV of 40 or less.
For geological reasons, the placement of a new ADU cannot be: 1)Within the critical root zone of a Heritage Oak; 2)Located on slopes that exceed 30 percent; 3) Within 25 feet of the top of a creekbank; 4) Within a recorded easement (open space, public utility, etc.); or 5) Within a geotechnical or seismic hazard zone.


For Detached units within 30’ of side or rear property lines, exterior entrance shall not face a side or rear property line.

Source Code:

Important Note: Rules and regulations are updated and changed frequently. It’s one of our jobs to be up to speed and navigate those regulations. Let us know if our website isn’t up to date or if you have any information that could help. Cheers!