Taking interest bearing loan.

Assalamu alaikum,. I have researched this dilemma on the internet and have yet to come to an understanding. Some say it is permissible to a degree and some say it is not permissible at all. It is as follows: My wife, my son and I live in a small home. It strains our "nerves", and sometimes causes arguments. Her Mother and Father will be coming to live with us soon. We need a larger home. Is it permissible to get a loan by conventional (US) methods with interest, with the intent on converting it to a Non-Riba loan in the future (Set time 5 years) we CAN do this but not now. Most require 20% down, and it would take us time we do not have to accumulate the 20%. If we rent we loose on the conversion (taxes) from going from a owned home to a rented one. I have checked all other avenues (Broker, Friends, Family) and their are no other feasible options. wa salaam