An assessee can claim deduction of Interest on Housing Loan to acquire house property u/s 24(b) and simultaneously HRA exemption on rent paid (if he resides in property other than acquired). Further, upon sale of said property, interest already claimed as deduction u/s 24(b) can be added to cost of property for the purpose of computing capital gain.
If your assessee is residing in the new house (own) from Jan-15, he/she can claim HRA till Dec-14 ( if the assessee paid rent) and for the period Jan-15 to Mar-15, interest on HL can be claimed subject to a maximum of Rs. 2 lacs.