San Francisco Legislative Update (2016): Accessory Dwelling Unit Ordinance Finds Additional Housing Stock in Existing Space


San Francisco’s new “Accessory Dwelling Unit” law – adopted in Ordinance 162-16 – is another effort in the City’s broader plan of trying to squeeze additional dwelling units out of existing inventory. Accessory Dwelling Units (also known as “ADUs”, “Secondary Units” or “In-Law Units”) are defined as dwelling units entirely within the existing built “envelope” of an existing building. (In other words, with the exception of allowing small height increases when ADUs are built in conjunction with seismic retrofit work, the addition cannot increase the size/height of a building.)

The Planning Code distinguishes between buildings with four or fewer existing dwelling units and those with more than four. For the former, one ADU is permitted, while there is no limit for the latter, so long as the additions conform with the ADU rules. These rules include the following:

• An Accessory Dwelling Unit cannot be constructed using space from an existing dwelling unit. They also cannot be merged with another dwelling unit;
• They cannot be created in certain Neighborhood Commercial Districts;
• They cannot be used for Airbnb/short term residential rentals;
• They cannot be converted to condominiums;
• While ADUs are necessarily “new construction”, they are exempted from vacancy control prohibitions under Costa-Hawkins, and this is the case whether or not the building in which the ADU is located is also “new construction”;

ADUs are, however, prohibited where the property owner has performed an owner/relative move-in eviction within five years or any other non-fault eviction – like the Ellis Act – within ten.