The number of residential building permits issued over the year ending in September increased 9.3 percent, according to data compiled by the Home Builders Association of Greater Des Moines. Creighton Cox, the organization's executive officer, said the numbers could show a 10 percent jump by year's end. The report also shows a trend for a decline in the construction of multifamily projects and an increase in single-family houses and townhouses. Apartment units dropped 23.5 percent over the year ending in September, to 1,119 from 1,463 in September 2012. Single-family construction increased 36.4 percent, to 2,410 as of September from from 1,767 for the year-ago period. However, the number of multifamily units in Des Moines virtually had a dramatic increase, to 577 from 113. Cox said construction of apartment buildings has leveled in Greater Des Moines with an improvement in the economy and rise of prices for existing homes, making new construction more affordable.