A nationwide network of home improvement installers has been acquired by Roark Capital Group, a private equity firm that owns some of the best-known restaurant franchises in the nation. Roark’s plans for The Home Service Store (HSS), which already provides installation services for Lumber Liquidators, Costco and BJ’s Wholesale Club, are equally ambitious; the Atlanta-based investment firm has put Robert Sheft, who helped develop Home Depot’s first foray into installed sales, in charge of its expansion plans.