Deduction of housing loan

Hi. Friends.. I wana ask 2 things. One of my relative took housing loan of 27lak. N now he is payng emi. He is still not in possession of house. My 1st question is- can he take interst part paid in emi as deduction ? Is their any condition other condtion? My 2nd question- what abt principal part? Is it claimed immediately in sec80c or wait till he get possession. Pls guide. Thanks