An estimated 40,458 homes and condos are sitting vacant in San Francisco, and that number could potentially go down if the city were to introduce a vacancy tax that would fine homeowners who leave their properties empty, a new report released Monday by the city’s budget and legislative analyst said.

The report was commissioned by Supervisor Dean Preston, who wanted to take a deep look at the scope of residential vacancies in San Francisco and explore whether vacancy tax policies adopted in other cities could help ease SF’s housing shortage.