Chairman Bob Carlton-Porter said that the jumps in profit and turnover were a direct result of the acquisition of Llewellyn last September for £16.2m.
He said: "These increases were contributed to by Llewellyn, whose performance has exceeded our expectations. Llewellyn's construction turnover and operating profit before goodwill for the first half were driven to £76.1m and £1.2m respectively."
ROK announced that it has appointed Ashley Martin to the board as finance director. Martin was finance director at media group Tempus. Carlton-Porter said: "Ashley brings with him a wealth of experience of building businesses by acquisition."