Total existing-home sales transactions that include single-family homes, townhomes, condominiums and co-ops, slipped 1.3 percent to a seasonally adjusted annual rate of 5.44 million in July from a downwardly revised 5.51 million in June. July's sales pace is still 2.1 percent above a year ago, but is the lowest of 2017.

Lawrence Yun, NAR chief economist, says the second half of the year got off on a somewhat sour note as existing sales in July inched backward. "Buyer interest in most of the country has held up strongly this summer and homes are selling fast, but the negative effect of not enough inventory to choose from and its pressure on overall affordability put the brakes on what should've been a higher sales pace," he said. "Contract activity has mostly trended downward since February and ultimately put a large dent on closings last month."

The median existing-home price for all housing types in July was $258,300, up 6.2 percent from July 2016 ($243,200). July's price increase marks the 65th straight month of year-over-year gains.