If you intend to take HDB loan for the purchase, the answer is yes. You need to fork out 50% of cash proceed. Pls note that this is cash proceed, not sales proceed. Your CPF proceed will also be fully utilised on the new purchase.
However, if you decide to take a bank loan, you will need to put in 5% of valuation cash and the balance 15% in CPF.
Hope that I had answered your question.
Feel free to contact me if you need my assistance.
Thanks and Regards
Dennis Wee Realty Pte Ltd