Median home prices have increased 2.9 percent to $674,000 this year in Westchester. In Rockland, prices are up .15 percent to $496,250, while in Putnam prices fell .15 percent to $404,380. Sales of single-family houses increased 5.5 percent in the third quarter in Westchester and 1.5 percent in Rockland. House sales were flat in Putnam. “We are not seeing evidence that the subprime problem or the credit crunch are having a meaningful effect on this market, in terms of sales or prices of homes,” said P. Gilbert Mercurio, Westchester County Board of Realtors CEO.