Building a house in a marriage-like partnership - How do partners secure themselves?

Dear forum, I am seeking advice in the following situation:

My partner and I are unmarried. We are currently building a house on a plot of land that belongs to me alone. Value of the plot ~ 150 TEUR. In addition, we have taken out a construction loan of ~ 300 TEUR, for which we are jointly and severally liable. So that my partner does not end up "with nothing" in case of separation, we are considering transferring 35% of the plot to her. This is based on our (non-expert) assessment that with a total value of the property of ~ 450 TEUR at time x, she has paid roughly half of the loan or of the loan portion repaid by then. In case of separation, we would notarize that she (subject to the bank's approval) transfers the ownership share back to me and I pay her half of the loan portion repaid by then in return. The interest paid would then be

As far as I understand correctly, for this transfer of ownership between unmarried couples, in addition to the fees for the notary and land registry office, real estate transfer tax or gift tax may also be incurred?

Are there any other possibilities to adequately protect both partners in our situation? (Except for marriage, which is not excluded but currently not planned :))

Thank you very much for the advice.

The interest paid would then be

to be seen as a kind of rent. (Clicked send too quickly)

Put everything in a partnership agreement. Why do you always have to be married. ;-)

Attention - Tax Traps!!!

If persons A and B (unmarried) build a house and, for securing the other party, e.g. take out a term life insurance, then inheritance tax may apply, and not insignificantly. Not only for the house. Also for a possible insurance payment! And loans cannot be offset.

Get intensive advice from a specialist about the disadvantages of "not being married" and be aware of these problems or resolve them.

Keyword e.g. policyholder ≠ beneficiary!

Put everything in a partnership agreement.

And with that you can avoid inheritance taxes? That's new to me.

And with that you can avoid inheritance taxes? That's new to me.

I must have overlooked that part of the OP's post. Somehow assumed he was getting at something else. Sorry.