Buy a single-family house - mortgage a condominium unit and sell it later?

You have to as well. Otherwise, you will have a problem paying your bills if there is no money in the account.

And this is exactly where the problem lies: 1. If it were "only" 55k to be financed variably, I wouldn’t even think twice. But with 150-300k, that’s at least €375 per month. 2. Who guarantees that I will receive this amount in 1 1/2 years? I don’t expect a significant decline, but what if 50k is missing in the end? Both have their advantages and disadvantages.

Who guarantees me that I will receive this amount in 1 1/2 years?

That is why a buffer is also included. Increase long-term financing by T€ XXX.

That is why a buffer is also included. Increase long-term financing by T€ XXX.

hm, do I understand correctly that the „actual“ financing is then increased by 30k to have a buffer for the variable loan (selling price lower than expected?) Does the bank give more money than it has to? I thought you then have to submit receipts for everything. There is a cost breakdown, etc. So far I haven’t spoken to any bank that financed a buffer.

So far I haven’t spoken to any bank that financed a buffer.

Then let’s put it another way. Calculate a conservative sales revenue that is simply €30,000 lower than before. And you already have a buffer. Nobody ever calculates to the last cent. Apart from that, every bank finances a buffer. Just give it the name "special equipment" or whatever.