 Oakland expanded during the 1920s, as its population expanded with factory workers.Approximately 13,000 homes were built in the 3 years between 1921 and 1924, more than during the 13 years between 1907 and 1920.Many of the large downtown office buildings, apartment buildings, and single-family houses still standing in Oakland were built during the 1920s; they reflect the architectural styles of the time.