Hello Roger,
Our thermal engineer says KfW 55 can only be achieved with 0.7 windows. If both are much worse than 0.7 windows, then this is definitely decisive for the calculation and must be considered. Thanks for the info.
KfW 55 does not depend solely on the value of the glass; how could it? Where, for example, certified RC II windows are installed, the value shoots up so much that - if your energy consultant were right - no KfW 55 efficiency house with certified windows would be possible. Since this is not the case, your consultant is mistaken on this point or you may not have understood him correctly.
What about the floor-to-ceiling window doors in your attic or upper floor; I don’t know which house type you are building. Do you have French balconies planned there or mullion elements? If the latter, the glass value no longer matches your energy consultant’s statement either. Unless you have installed PH windows; then it also works with laminated safety glass.
The Ug value of the glass, for example in our windows with triple glazing, is 0.6 watts/m2K. This value looks nice - and it is, yet the U-value of the window must still be considered. When installing safety glass (laminated safety glass, VSG), it is already 1.2 watts/m2K. Building a KfW 55 efficiency house requires (based on our building specifications) for the pure masonry "only" insulated bricks, insulation under the base plate (from my personal point of view the biggest nonsense in house construction at all) and supervision by the external expert. Either way, a daylight spot 35 x 35 cm with single-pane safety glass does not affect the verification.
Rhenish regards