In common with other Eastern European countries, Bulgaria has suffered a serious urban housing shortage since World War II, although large reserves have existed in rural housing. Great numbers of workers have left the villages over the years to find employment in the rapidly expanding industrial centers, but housing construction has not kept pace with this migration. During the early years of communist rule, priority in the allocation of scarce building materials and funds was given to the building of new plants and other industrial installations rather than to new housing. In the 1960s only between 3 and 6 percent of the gross national income was invested in housing construction as compared with 20 percent or more in most Western European countries. Bulgaria has had the lowest housing investment among the communist countries of Eastern Europe. In 1970 the Politburo and the Council of Ministers adopted a special program for the solution of the housing problem within the next ten to fifteen years. The program stated that the aim of the BKP was to enable every family to have its own apartment, and every member of the family his own room. In 1972 there were some 250,000 more urban families than there were housing units. Aggravating the housing shortage in the early 1970s was an accelerating deterioration of old buildings. Money and materials for maintenance of existing structures have been even scarcer than for new buildings. In addition, many of the postwar apartment buildings were put up hastily, using inferior materials and workmanship, and soon turned into crumbling slums. In order to spur housing construction without imposing too great a burden on the state budget, the government was forced to abandon its intention of providing low-rent housing for everyone. Instead, it has encouraged the population to invest in its own housing. As a result, special savings accounts for the purchase of private housing have grown at a more rapid rate than regular savings accounts. During the 1968-70 period approximately one-third of the new housing units made available were financed entirely by state funds, another one-third were financed entirely by private funds, and the last one-third were financed by private funds with the aid of loans from state sources. State enterprises are instructed to grant their employees interest-free, fifteen-year mortgages for the purchase of an apartment or house. Up to 4,000 leva can be borrowed for this purpose in urban areas and up to 3,000 leva in rural areas. This, however, covers less than one-half of the cost of a two-room apartment.