Almost half of single-family houses in the New York and Washington metropolitan areas are losing value, a sign that buyers' tolerance for high prices in many large U.S. cities may be reaching a limit.

The values of 45 percent of houses in both the Washington and New York areas slumped by at least 2 percent in June from a year earlier, according to a new index created by Allan Weiss, co-founder of the Case-Shiller home price indexes. In June 2014, only 15 percent of Washington residences dropped in value, while 20 percent fell in New York. Because the index is of only single-family homes, it doesn't include Manhattan. More properties also were in decline in Los Angeles, Chicago, Phoenix and Miami. 

A steady rise in U.S. home prices since the bottom of the market combined with weak income growth has made housing less affordable, especially in big cities. Credit remains tight and demand is now being driven primarily by buyers dependent on mortgages, as foreign buyers and investors pull back from the market.