In 2014, San Francisco passed legislation allowing property owners to add accessory dwelling units, or ADUs, to their homes and buildings. The law was then expanded in late 2016 so that any building with at least five existing apartments could add an unlimited number of units, the San Francisco Chronicle reports.

As property owners take advantage of the new law, the city has seen an explosion of ADUs over the past year. "There are now 1,046 ADUs in the pipeline, with building permits approved for 531 of them," according to the Chronicle.