Source: US. Bureau of the Census
Release: Housing Vacancies and Homeownership
Included in this category are year-round units which were vacant for reasons other than for occasional use, and units Occupied by persons with usual residence elsewhere. For example, held for settlement of an estate, held for personal reasons, or held for repairs.
US. Bureau of the Census, Housing Inventory Estimate: Vacant Housing Units Held Off the Market and Vacant for Other Reasons for the United States [EOTHUSQ176N], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/EOTHUSQ176N, October 21, 2016.