Hello Phil,
I am not an expert in these matters – especially since there are several ways to Rome – but I can answer you from my professional experience.
Our KfW 70 efficiency houses are equipped with the following standard values for the building envelope:
Floor slab: 0.26 W/(m2K) => reference building 0.35 W/(m2K)
Windows (glass and frame): 0.9 W/(m2K) => reference building 1.3 W/(m2K)
Wall (36.5 monolithic): 0.23 W/(m2K) => reference building 0.28 W/(m2K)
Roof: 0.17 W/(m2K) => reference building 0.20 W/(m2K)
Considering the thermal bridges => 0.05 W/(m2K) => we usually achieve a calculated primary energy demand of Q 58.3 kWh(m2a) [reference building Q 83.41 kWh(m2a)] when using an air-water heat pump and if the building is not located on the Zugspitze; see attachment.
However, we already cover other values from the BB by default; the 200 mm insulation in your list is only one of several points in which we probably differ.
If a builder wishes to install a gas condensing boiler with solar heating support, they can generally assume that this is not sufficient to achieve the KfW 70 status; usually, the installation of a ventilation system with heat recovery is required. This is sufficient in most cases to qualify for the KfW promotional loan; in very rare cases (depending on the location), additional insulation must be added. In the next step (KfW 55, attachment), only a ventilation system with heat recovery as well as a filled block with the value 0.20 W/(m2K) are missing.
I wrote at the beginning that there are several ways to Rome; this is to be taken literally because there are several calculation methods to provide the KfW proof. And then there are differences in the persons who provide the proof. We have structural engineers who calculate concrete in water and others who orient themselves on the actual conditions. Since ultimately everything depends on the paperwork, it is quite possible that your planner belongs to the first category or takes the “apparently” worse calculation method.
Subject KfW 70 efficiency house – As long as the subsidies are secondary for you (they are not really much cheaper at the moment anyway), I would not worry too much. A single-family house built according to the Energy Saving Ordinance is not really bad; from my personal point of view, it is often the better choice, considering the not exactly small monetary effort. What is important in my opinion is not that the paper says “You have built a single-family house subsidized according to KfW 70,” but the actual energy consumption. In case of sale, this will interest a potential buyer more than anything else.
Rhenish regards
