completion of house

hi experts if i have constructed house in oct 2009 and i m residing in that house. which date should i take the date of completion for the purpose of claiming interest u/s 24 . do i need to get any completion certificate from any authority. suppose the concerned authority does not give me that certificate due to some violation done by me or it take long time to issue the certificate due to some vested interest. then can i claim interest . one more query when my employee want claim the interst loss in his salary should i allow that interest without getting completion certificate while calculating tds liability of the employee. pls reply if sure.