(ShareCast News) - SIG has confirmed that Doug Robertson will retire as group finance director at the end of the month and leave the company on 28 February following a handover period.The supplier of insulation, roofing, and specialist construction products said he will be succeeded by Nick Maddock, who will join the group on 23 January.Maddock will be appointed as a director of the board on 1 February.At 1510 GMT, the shares were down 3.8% to 104.80p.