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Los Altos Hills ADUs

Everything about building Accessory Dwelling Units in Los Altos Hills, CA

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Los Altos Hills ADU Guidelines Last Updated 04/05/20

PLANNING OFFICE The city planning office is not open to the public at this time, but is accepting ADU permit questions and applications.

The city government of Los Altos Hills will approve ADUs under California's statewide mandated regulations.
The California Building Code (CBC) 2019 is adopted.
Relevant state bill updates for SB13, AB68, AB881, AB670 are shown in green below.


City Hint: The city has not yet responded to requests for ADU permit volumes for the past year, but they will be provided here once response has been received.

Number of ADUs allowed:

According to state law, all single-family homes are allowed at least one ADU. Additionally, single-family lots which are owner-occupied may create one ADU and one Junior Accessory Dwelling Unit. Also, multi-family lots may now add one ADU per every four existing residential units, so long as they were legally established.

As of January 1st, 2020

Types of ADUs allowed:

Detached ADU, Attached ADU, Junior ADU are permitted. ADUs may be new construction or converted from existing space. Junior ADUs must be converted from existing space.

Lot size:

Accessory Dwelling Unit (ADU) projects on single family or multi-family residential parcels will not be subject to the minimum lot size of the underlying local zoning code or by special ordinance. ~ According To AB68

As of January 1st, 2020

ADU size:

Single-family and multi-family Parcels will be permitted to add up to 850 square feet for a one bedroom ADU or up to 1,000 square feet for a two bedroom ADU, regardless of the underlying zoning standards of the property. A Junior Accessort Dwelling Unit (JADU) up to 500 square feet is permitted. The minimum size of any living unit (including ADUs and Junior Accessort Dwelling Unit (JADU)s) is 150 square feet according to Califronia Residential Code. ~ AB68

As of January 1st, 2020


Setbacks for a detached new construction Accessory Dwelling Unit shall be no more than 4 feet from the rear and side lot lines. No setbacks shall be required for Accessory Dwelling Units and JADUs converted from legally eastablished existing space. Attached new construction Accessory Dwelling Units and conversions from existing space to be expanded must comply with the setbacks of the underlying zone. ~ AB68

As of January 1st, 2020


Replacement parking shall not apply to properties which convert an existing garage to an Accessory Dwelling Unit (ADU) or Junior ADU. ~ AB68 & AB881 Update

As of January 1st, 2020

Fire Safety:

Per state minimum requirements.

Shape, materials and style:

A ADU shall be subordinate to and architecturally consistent with the
primary dwelling;

The purpose of Code provisions regarding accessory structures and ADUs is to assure that such structures are subordinate to and compatible with the main residence on a lot;

If the ADU is within or attached to the primary dwelling, it shall be
constructed so that the entire structure appears to be one (1) dwelling;If the ADU is separate from the primary dwelling, it shall not be sited in a
visually prominent location, and shall respect the visual and acoustic privacy of primary dwellings on contiguous lots;


Height will be restricted to the maximum height of the underlying zone.

Design review:

Ministerial review Process per state standards.

Number of Bedrooms:

Not specified by State Standards.


Owner-occupancy will not be required for new Accessory Dwelling Unit (ADU)s (conversion and new construction) built between 2020 and 2025. ~ Updated: State Law SB-13

As of January 1st, 2020

Utility connections:

The lot on which an ADU is located must be connected to the public sanitary sewer system or have a private sewage disposal system that is deemed to be adequate for the addition of the accessory dwelling by the Santa Clara County Division of Health Services; and must have an adequate water supply;

Permit Fees

SB13 Update: As of January 1st, 2020, local impact fees for ADUs will be reduced substantially statewide.


“Secondary dwelling” means an attached or detached residential dwelling unit which provides complete independent living facilities for one (1) or more persons. A secondary dwelling shall include facilities for living, sleeping, eating, cooking, and sanitation, and be located on the same parcel under the same ownership as a primary dwelling. (§ 1, Ord. 305, eff. October 3, 1986; § 1, Ord. 327, eff. December 10, 1989)


Any vehicular access to a secondary dwelling shall be by a common driveway with the
primary dwelling;

Allowed Zones:

*** Beginning in 2020, according to state law, all residential zoning districts, including single-family and multi-family, are allowed to build Accessory Dwelling Units. ***

As of January 1st, 2020

Open Space & Views

The views of prominent scenic features by primary dwellings on contiguous lots shall be

Street & Traffic

The secondary dwelling shall not have a significant adverse impact on traffic flow and

Existing Structures

The Site Development Authority may determine that an accessory structure which does
not contain all of the elements of a “secondary dwelling” per the Zoning Code definition,
could readily be modified or used for independent living purposes. In such a case, the
Site Development Authority may, at its discretion, require a property restriction to be
recorded against the property title, limiting the use of the structure so that is it not
modified to a "secondary dwelling". The language of the restriction shall include
provisions for Town inspection and enforcement of this provision.

SB13 Update: Amnesty program to permit unpermitted units will be administered statewide, allowing non-health and safety code violations to be deferred.

Residential Building Code:

The California Building Code (CBC) 2019 is adopted.

Los Altos Hills City Planning Offices


26379 Fremont Road Los Altos Hills, CA 94022 Los Altos Hills, CA 94022

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Size: 500 sqft


Appreciation Estimate = (Base Value: $) / (Home's Living Space: sqft) * (ADU's Living Space: sqft)

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