Again: it’s not about the monthly rate itself (by the way, we can also change the repayment twice), but rather about the fact that I can set an interest rate today that can be used in ten years if the normal interest rate rises. The building savings contract doesn’t have to be fully saved up, I could also continue to finance with it!?
Exactly that problem has already been addressed several times here. If the saver does not save up enough so that they are entitled to allocation in 10 years, then you have no interest rate security at all, but you have to take out an expensive interim financing in 10 years (which can be dictated to you by the bank), while your saved money waits in a poorly interest-bearing building savings contract until it is entitled to allocation. Only when the building savings contract is entitled to allocation is the loan/interim financing redeemed and you can then make use of the favorable loan from the building savings contract.
If the building savings contract is just entitled to allocation in 10 years and you could not pay installments into the building savings contract for one year, then it’s simply not enough if you pay double your installments into the building savings contract the following year, because you still don’t have the same valuation number.
Since I’m still not sure whether you have understood the building savings system, I want to point out again that you cannot compare the interest rates quoted by the building society with interest rates from annuity loans.
How long is the building loan actually planned for? Usually, that’s not much longer than the savings phase.
You would have a similarly long interest rate security with a 20-year loan.