House and condominium sales in Rhode Island went in different directions during May, with the former following the regional trend downward and the latter rising sharply, according to a Boston-based research firm.

Sales of single-family houses fell 10.5 percent in May when compared with the same month last year and were off 5.4 percent for the first five months of the year, according to a report released yesterday by The Warren Group. The drop in May followed an April decline of 5.6 percent.

But condominium sales rose significantly during May, rising 18.8 percent when compared with May 2006. It was the second straight month of sharp sales increases. Condo sales rose 24.6 percent in April.

From January to May, condo sales are up 6.6 percent.

“We continue to see sales of single-family homes struggling a bit, but condominium sales in Rhode Island are providing stability to the market,” said Timothy Warren Jr., chief executive officer of The Warren Group, which publishes Banker & Tradesman and other business periodicals.

There were 3,450 sales of single-family houses in the first five months of the year, with 867 occurring in May. Last year, there were 3,648 single-family house sales, with 969 of those taking place in May, The Warren Group said.

By contrast, 1,000 condo units were sold from January to May of this year, with 266 coming in the last month. Last year, 938 condos sold during the five-month period, with 224 occurring in May.

Monthly condo sales have been fairly consistent since January 2005, the report showed, with sales hovering around 250 units during the spring and summer.

An analyst for The Warren Group was at a loss to explain why condominium sales shot upward in May, describing it as “a little bit of an anomaly.”

“Although sales are up . . . that doesn’t necessarily say the condo market is immune to the softness of the real-estate market,” said Terry Egan, editor in chief of publications at the Warren Group.

That softness is illustrated in the median sales price, which fell 8 percent for May, from $250,000 to $230,000, according to the report. Year to date, the median price dropped 4.4 percent, from $235,250 to $225,000.

House prices remained steadier during the five-month period, with the median falling 1.9 percent from $265,000 last year to $260,000 this year. The median price for May fell 2.4 percent, from $267,500 to $261,000.

The sales figures do not take into account incentives sellers may offer to close a deal, a strategy being employed in many places across the country during the current real-estate downturn.

Sellers are offering to pay closing costs on real-estate transactions and raising the money allotted for property improvements, such as new rugs or paint, Egan said.

“Even with existing home sales, we’re hearing from Realtors that incentives and concessions are becoming much more prominent,” Egan said.

Single-family house sales are likely to remain soft for the remainder of the summer, he said, until the effects of subprime mortgages finish working their way through financial markets and interest rates remain volatile.

pgrimald@projo.com