Calculation of KFW40+ criteria - Update

We have now received information from our energy consultant that our photovoltaic system needs to almost triple and the storage has to double. Our (finished) house provider will cover the costs, but we are still wondering how such a major change came about. Do I need to worry about the insulation of the house?

Have you already started building? Normally, the calculated values at the time the calculations or the preliminary energy certificate are created apply. I know that the limit values are occasionally tightened. Have you made any changes that would require a new calculation? Or did the house builder exchange any materials if he is already voluntarily covering the additional costs?

The planning is completed to this extent, but there has not yet been a groundbreaking on the property. Since the planning was not finished when submitting the KFW application, different values were used here, which have now been adjusted after the planning was completed, resulting in this change—so the explanation goes. Compared to the submitted application, the living area has increased by about 5 sqm and the window area has become slightly larger. The takeover was also not voluntarily done directly, but if I agree to a fixed price for a KFW-subsidized house, then the provider has to live with it if it becomes more expensive, just as I have to live with it if the sinks they sold me for 300€ only cost 100€ in the offer. Moreover, the originally planned photovoltaic system costs about the same as the larger photovoltaic system on the open market..

If he owes you a subsidized house, and the changes can be explained by more window areas - as well as the occasionally tightened limits - I wouldn’t worry about the insulation. In our experience, the technical components have a greater impact on the calculation... The general contractor has to do a Blower Door Test anyway for the KfW, and the energy consultant sets the BnD based on his submitted calculations. Congratulations on the larger photovoltaic system without extra charge, I would say ;)