Extension of a 1960s house and energy-efficient renovation

Honestly, it is not intended for renting out

But if you ever want to move before it’s paid off, then a tenant would definitely be helpful. And they don’t care whether it’s okay according to your taste to go from the bedroom through the dining room to the balcony. Rather, they find another apartment with a better layout more appealing.

In that sense, I wouldn’t want to "create" a only moderately attractive property just for "owner-occupancy".

In the second draft (OG), the bedrooms would be located in the attic. These rooms are accessed via the staircase in the hallway. This way, there would be no corridor shaped like a tube. However, in this concept, there is a room between the living/dining area and the balcony that I am not quite sure how to use yet.

The description in your initial post is a bit confusing to me. On the other hand, I mentioned that the ground floor should be uploaded as a jpg at some point.
What is missing for clarity is a site plan of the property, existing building and proposed extension in a different color.
Also floor plans of the existing building and new walls in a different color, and if applicable demolition.

Your 3D looks and will probably be too bulky in reality.
In the 3D view, there is also an extension on the ground floor (east): who will use this?
Wouldn't it be more sensible to place the entrance to the upper floor in the extension on the east?
What I took away: 7.5 meters total height... that means you would hardly have a standard room in the attic.

Best regards, Yvonne

Basically, for a project like this I would use an architect, who with much more sophistication and skill is able to get the ultimate out of the [BePlan] and your requirements.

You can post his draft here.

Regards, Yvonne