Hello, is it advisable for me to voluntarily contribute additional money into my CPF even though my BTO down payment is coming up?

Mortgage loan is one of the cheaper loans you can find. And in the case of BTO/HDB, you can never refinance the loan.

In general, I would suggest you do not voluntarily contribute at this point. In the past, there will be people who would even buy investments with CPF-OA to lock up the money, let the downpayment happen, then sell the investments. I don't think you should do that either though.

The biggest reason is that you would want to keep excess CPF-OA monies, and cash on hand, in case of any emergencies like job loss, or being unable to service the mortgage. In the case of keeping cash on hand, you would probably need it for various stuff, such as renovation, daily expenses, etc.

Best to sit down and draw out your budget. Understand how much reserve buffer you have, and anticipate any near term large expenditure.
If you would like, you can schedule a goalsmapper session with me, and you would get a chart similar to the one attached. https://rplg.co/gmconsult

No, I won't do it.

I am going to need cash for

1. renovation
2. furniture
3. electric appliances.
4. Downpayment for the flat too.....

If you pay the housing loan from CPF, when you sell the flat, you have to return to the CPF Board. If you pay the house loan from CASH, when you sell the flat, the proceeds can return to you as cash.

When you get back the cash in 5 yrs or more when you want to sell, it's up to you whether you like to use the cash for other reasons or contribute to your CPF.

If you had sent the cash to CPF, and then use CPF to pay for the housing, you have no choice, the sales proceed of this portion would be paid back to your CPF account whether you like it or not.