Source: US. Bureau of the Census
Release: Housing Vacancies and Homeownership
This group consists of vacant units offered for rent and those offered both for rent and sale.
US. Bureau of the Census, Housing Inventory Estimate: Vacant Housing Units for Rent for the United States [ERENTUSQ176N], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/ERENTUSQ176N, July 24, 2016.