A surging home-purchase market helped boost new single-family business volume at Fannie Mae and Freddie Mac in May, according to a new ranking and analysis by Inside The GSEs.Together, the two companies issued $62.03 billion of single-family mortgage-backed securities in May, an unspectacular 6.3 percent increase from April. In fact, May’s volume was the second lowest monthly production of the year. But that’s because the early months of 2017 were still heavy with refinance business. Purchase-mortgage business at Fannie and Freddie was up a solid 15.5 percent from April, hitting $36.78 billion, tops so far in 2017. Meanwhile, Fannie and Freddie securitized just $23.98 billion of refinance loans in May.