Generally speaking, a property owner can add additional dwelling units to their parcel up to the limits of zoning density. However, a series of policy and legislative changes starting with a Mayor’s Executive Directive in 2013 sought to maintain existing dwelling units, whether or not they were permitted and/or exceeded allowable density. That directive dictated that Building and Planning implement discretionary review analysis prior to removal of unauthorized units.
2014 saw the addition of a City-wide “in-law unit” legalization program to provide a path to legalization for an estimated 30,000 to 40,000 units in the City that “often meet life and safety standards, and may require only exceptions from density. open space, and other Planning Code requirements in order to become legal”.
2016 brought the first ADU law, which, like the 2014 ordinance, provided a density bonus, but did not require the unit to have existed prior to 2014. (In other words, if the prior ordinance was about grandfathering in existing units, the ADU ordinance was an incentive to create them.) Coupled with the 2016 ordinance requiring, for the first time, conditional use authorization from the Planning Commission to remove authorized or unauthorized units, San Francisco has taken an aggressive approach to adding to its housing stock.