Slowed by frustratingly low inventory levels in many parts of the country, existing-home sales lost momentum in July and decreased year-over-year for the first time since November 2015, according to the National Association of Realtors (NAR). Only the West region saw a monthly increase in closings in July.

Total existing-home sales, which are completed transactions that include single-family homes, townhomes, condominiums and co-ops, fell 3.2 percent to a seasonally adjusted annual rate of 5.39 million in July from 5.57 million in June. For only the second time in the last 21 months, sales are now below (1.6 percent) a year ago (5.48 million).

Lawrence Yun, NAR chief economist, said existing sales fell off track in July after steadily climbing the last four months.

“Severely restrained inventory and the tightening grip it’s putting on affordability is the primary culprit for the considerable sales slump throughout much of the country last month,” he said in a statement. “Realtors are reporting diminished buyer traffic because of the scarce number of affordable homes on the market, and the lack of supply is stifling the efforts of many prospective buyers attempting to purchase while mortgage rates hover at historical lows.”

Adds Yun, “Furthermore, with new condo construction barely budging and currently making up only a small sliver of multi-family construction, sales suffered last month as condo buyers faced even stiffer supply constraints than those looking to purchase a single-family home.”

The median existing-home price for all housing types in July was $244,100, up 5.3 percent from July 2015 ($231,800). July’s price increase marks the 53rd consecutive month of year-over-year gains.

Total housing inventory at the end of July inched 0.9 percent higher to 2.13 million existing homes available for sale, but is still 5.8 percent lower than a year ago (2.26 million) and has now declined year-over-year for 14 straight months. Unsold inventory is at a 4.7-month supply at the current sales pace, which is up from 4.5 months in June.

“Although home sales are still expected to finish the year at their strongest pace since the downturn, thanks to a very strong spring, the housing market is undershooting its full potential because of inadequate existing inventory combined with new home construction failing to catch up with underlying demand,” said Yun. “As a result, sales in all regions are now flat or below a year ago and price growth isn’t slowing to a healthier and sustainable pace.”

The share of first-time buyers was 32 percent in July, which is below last month (33 percent) but up from 28 percent a year ago. First-time buyers represented 30 percent of sales in all of 2015.

All-cash sales were 21 percent of transactions in July, down from 22 percent in June, 23 percent a year ago and the lowest share since November 2009 (19 percent). Individual investors, who account for many cash sales, purchased 11 percent of homes in July, unchanged from June and down from 13 percent a year ago. Seventy percent of investors paid in cash in July.

According to Freddie Mac, the average commitment rate for a 30-year, conventional, fixed-rate mortgage dropped from 3.57 percent in June to 3.44 percent in July. Mortgage rates have now fallen five straight months and in July were the lowest since January 2013 (3.41 percent). The average commitment rate for all of 2015 was 3.85 percent.

NAR President Tom Salomone, broker-owner of Real Estate II Inc. in Coral Springs, Florida, says in addition to affordability concerns, an issue seen earlier in the housing recovery may be reemerging. Realtors are indicating that appraisal complications are appearing more frequently as the reason why a contract signing experienced a delayed settlement.

“Appraisal-related contract issues have notably risen over the past year and were the root cause of over a quarter of contract delays in the past three months,” he said. “This is likely a combination of sharply growing home prices in some areas, the uptick in home sales this year and the strong refinance market overworking the already reduced number of practicing appraisers. Realtors are carefully monitoring this trend, and some have already indicated they’re extending closing dates on contracts to allow extra time to accommodate the possibility of appraisal-related delays.”