Many of these apartments — also known as “granny flats” or accessory dwelling units (ADUs) — provide perfectly adequate housing and are among the most affordable accommodations in a city where home values average nearly $1.3 million and the average rent is almost $2,700, according to Zillow.

During a four-year pilot program that started Wednesday and extends through 2028, Berkeley homeowners can approach city planners about getting unpermitted accessory units inspected for safety, and legalized, while being assured that the process will be confidential and no penalties will be assessed on the previously undocumented apartment.