St. Helena Municipal Code Chapter 17.116,030: Accessory Dwelling Units

A.    An accessory dwelling unit shall meet the design and development criteria described below:

1.    Accessory dwelling units are allowed in any zoning district that allows residential uses insofar as there is an existing single-family residence on the lot;

2.    Each accessory dwelling unit shall meet the requirements for building height, setbacks, yards and lot coverage for principal buildings of the zoning district in which it is located, except that a detached accessory dwelling unit may exhibit a minimum side yard and rear yard setback of five feet. However, detached ADUs, not meeting the setback requirements of the primary dwelling, are limited to a maximum height of fifteen (15) feet, unless built above an existing garage or resulting from the conversion of an existing structure which is taller than fifteen (15) feet in height;

3.    The design of the accessory dwelling unit shall employ a design compatible with the principal dwelling and shall be consistent with the principal dwelling in terms of form, massing, scale, and level of articulation;

4.    Any window or door on a second story shall be located and designed utilizing techniques that lessen the impacts on the privacy of adjacent properties. These techniques may include use of obscured glazing, window placement above eye level, windows and doors located toward the existing on-site residence or screening treatments;

5.    Accessory dwelling units are required to follow the same building and safety requirements as the principal dwelling;

6.    Accessory dwelling units are required to provide fire sprinklers only insofar as they are required for the principal dwelling;

7.    There shall be a minimum five-foot separation between a detached accessory dwelling and any adjacent structure or building;

8.    No passageway shall be required in conjunction with the construction of an accessory dwelling unit;

9.    The introduction of an accessory dwelling unit shall be subject to review and approval by the local health officer where a private sewage disposal system is proposed;

10.    Accessory dwelling units located on property listed on the City of St. Helena Historic Resources Master List and/or the California Register of Historic Resources (CRHR) and/or the National Register of Historic Places (NRHP) shall exhibit compliance with the Secretary of the Interior’s Standards for the Treatment of Historic Properties for Rehabilitation and shall further be subject to the standards enumerated in Chapter 17.92, if applicable. At the determination of the planning director, any application for an accessory dwelling unit located on a property listed in the City of St. Helena Historic Resources Master List, identified as potentially eligible for listing or previously listed in the CRHR or NRHP (except for those contained entirely within an existing structure) may be required to provide a historic resource evaluation and/or consistency analysis prepared by a qualified architectural historian to determine compliance with applicable standards.


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