The number of vacant housing units in the United States increased to a record 19 million in the first quarter of the year, up from 18.9 million in the fourth quarter, the Commerce Department reported Monday. About 14.5% of homes were vacant, with 4.4 million available to be rented and 2 million available to be sold. The vacancy rate for rentable units fell to 10.6% from 10.7% in the fourth quarter. The vacancy rate for homes ready to be sold was steady at 2.7%. In the past year, the housing inventory rose by 1.14 million to 130.9 million, while occupied homes increased by 1.07 million to 111.9 million.