Banks with a long interest-free provision period for new construction

Very interesting. Does that mean that the planning is separated from the construction itself, so you only have to pay for the planning up to the building permit at first, right? Do the solid/wood prefab house providers even go along with that?

With us, yes. 5% of the offer is the planning fee. This is then deducted from the contract for work.

One way to save on commitment interest could also be to "park" the amount not yet drawn after the end of the commitment interest-free period in the account (if it is with the financing bank). This probably incurs a custody fee, but usually, it is better than paying commitment interest. Of course, the risk is low if you are still well above the deposit insurance.