I find it normal that you don’t have the house 100% figured out from the start. It develops gradually. We currently live in a house built in 1958 with 110 sqm. The energy costs were initially 5000€ per year, after some renovations around 4000€. We live with a basement and radiators. Since we are used to that, we had planned the same for the new house. For us, it was important to reduce energy costs. At first, we thought we would simply build according to the energy saving ordinance with photovoltaic and storage. After several forum suggestions and conversations with home builders from recent years, a new picture emerged. Underfloor heating and central ventilation improve living quality. So we included it. A basement as a possible option to accommodate grandma in the future is simply too expensive at 100,000€. You can also build an extension in a few years, convert the attic, and make space for grandma on the ground floor, etc. So the basement was out. Now I have a house with controlled ventilation + heat pump + underfloor heating + photovoltaic with storage anyway. So why not try to go for the 40+ [KfW standard]. That does not fully make sense to me.