Is a personal loan for buying a house sensible?

The bank would consider that as equity, right?

No, it does not. It is included as a financing component in your KDF calculation, just like any other loan.

Find a bank that is listed as second rank in the land register.

Write something about the total amount and monthly burden.

What do you earn and why does the bank not give you the loan without a private person.

The bank comes in first position. There are simply financiers who take on different risks.

Except that you have a full repayment loan and are inflexible

Getting €70,000 at 2.5% interest. Only conditions: repayment in 8 years and registration of a land charge in the land register (subordinate to the bank).

Is there anything against that?

That will then be a monthly installment of about €800 just for this loan. Plus, of course, the registration costs.

What speaks against it is that you are taking on a very high total installment, but have not yet been able to save any equity. The installment doesn't seem to match the income. Are you sure you can and want to afford that?

Have you even spoken to a bank yet or did you just figure out the loan-to-value ratio on your own? Somehow I have the feeling there might be a thinking error here...

Otherwise, go to one of the big intermediaries, just because one bank rejects doesn’t mean every bank rejects. If no reputable bank can be found to finance the project, there is probably a good reason for that.

A private loan would be a no-go for me personally. A small interest-free amount from your parents is okay, but what you’re aiming for you should think about carefully!
I don’t think this counts as equity capital, it is a burden registered on the house. Also, when determining your max monthly rate, the repayment for the private loan is included.

It’s best to write down the actual numbers. Purchase price, ancillary costs, renovation costs, equity, loan amount ... then you will surely get a useful assessment of your project here.