Correct execution of thermal separation house/garage

Well, then I would simply choose floor-to-ceiling windows on the left side, possibly even fixed glazing, and for the bottom side the lift-and-slide door.

Why - the manufacturer did mention weight problems, and both of the mentioned house walls do not stand over exterior walls of the basement (?)

The energy consultant must prove the thermal bridges. For this, there are forms from [KFW] which must be filled out. Basically, many things are possible; in existing buildings, it is almost standard that the garage is attached without insulation, and [KfW55] is also possible. What thermal bridge surcharge does the form sheet result in?

: I don't think that the weight of the lift-and-slide door is the problem, because the specification regarding special thickness for the walls also applies to houses on a slab foundation, i.e. it's not something that would be due to our special construction. I suspect it has more to do with the fact that the HSTs have a significantly deeper frame – at least the models I have seen. Probably the construction depth is then at the edge or even exceeds the thickness of the timber frame and causes difficulties with fastening/stability. But this is only my suspicion; I have not received an explanation from the company – only the statement that it only works this way.

: So far, from the energy consultant's side, I have only seen a hand-drawn action plan painted over the architectural plans; I have the suspicion that a more precise calculation has (not yet) been carried out. I will have to ask how confident they are in their “experience values.”

But I thought that in the case of renovation of existing buildings, slightly different calculation methods than in new construction are also allowed?

The KfW standard does not change, regardless of whether it is a new building or an existing one, otherwise, for example, there would have to be 2 different KfW55. I would always make sure that calculations are done according to DIN EN 18599. It is not a greater effort with one zone, but the results are much more accurate. In new buildings, everything is often simpler because thermal bridges are already taken into account according to Annex 2 of the standards, provided the architect has ever dealt with thermal bridges.