So the OP is quite aware of what he is signing up for :-) It is definitely NOT a building savings financing, it is a completely normal annuity loan, the rate remains constant, the ratio of interest and repayment shifts accordingly. The repayment schedule and contract conditions are available. And the interest rate is anything but insignificant. We are done in 24 years without special repayments. It is an offer from BHW, mediated by a financial service provider. The building savings contract for the residual debt of the KFW loan after 10 years was our idea, by the way :)