Single-family mortgage business at Fannie Mae and Freddie Mac grew substantially from July to August, according to an Inside The GSEs analysis of mortgage-backed securities data. The two firms issued $79.34 billion of single-family MBS last month, a 20.5 percent increase from July’s volume. That brought year-to-date volume to $523.40 billion, down 6.1 percent from the first eight months of 2017. [Includes two data charts.]