Is it possible to renovate a residential house from 1954 into an energy-efficient house? How?

Honestly: with the external dimensions and the floor plan, I would rather advocate for demolition and new construction. Even with an extension, it is hardly possible to come up with a reasonable solution for a family.

Honestly: given the exterior dimensions and the floor plan, I would rather advocate for demolition and new construction.
Even with an extension, it is hardly possible to find a reasonable solution for a family.

That may be true for some people, but a Town & Country 1.5-story 90 or 100 sqm doesn't have more space either and it's definitely enough for the three of us.
That's my opinion.

there where the window is placed in the kitchen on the drawing

Which window: the eaves or the gable side?

but as said, still in the idea phase.

As said, just post the plot here, then like-minded thinkers will gladly join.

Honestly: with the external dimensions and the floor plan, I would rather advocate demolition and new construction.

No demolition. I see the roof as needing a complete reconstruction and adding a knee wall in the process. A possible linear extension should be examined more closely.

The charm of the little house can be preserved and transformed and, in my opinion, is worth the effort, which will hardly be less than that of a newly built house paid for by credit card.

Which window: the eaves side or the gable side?

The eaves side window, I will try to get a few pictures over the weekend.

hello us again, nearly a month has passed since we wrote something here, I wanted to post a layout plan of the little house here again.

the gray roof areas are the extensions, the smaller of the two should be demolished, there is a veranda that makes the hallway and everything else very dark.
In the larger extension there is the bathroom and a living room, the bathroom is to remain with an additional skylight and the living room is to be opened to the current living room to create one room.

We had an architect come by to discuss the basic feasibility, spent an hour walking through the house, looked, measured, and laid out our ideas so he could make a rough cost estimate.

The result was the table listed below with which we cannot start according to my ideas. Cost point 180 € for this
and then also miscalculated, or rather, it is not clear in which total the windows are included etc.

here is a veranda which makes the hallway and everything very dark.

Extend the series of visual representations with photos - and with two more paintings: ground floor (existing) and upper floor (planning).

it is not visible in which sum the windows are hidden

I don't see them included there at all.