Thank you very much for your answers. I will try to respond in order:
Thank you for the tip. Indeed, we wanted to swap the fixed element with the sliding door to the kitchen so that you can go directly from the kitchen to the terrace.
We have considered what all needs to be stored. That might be everything on the ground floor from winter jackets, skis to tablecloths, decorations, and similar items. Upstairs, for example, we would like to store bed linen, suitcases, and similar things. It just adds up. As a result, of course, there is more space available in the bedroom (or you can make do with less) because no suitcases, bed linen, etc. have to be stored there. A purely practical question for you: why do you have large bedrooms? We thought that people don't spend much time awake in them anyway (don’t walk around there…) and if everything is cleverly stored in wardrobes etc., why would you still need free space? We currently have a pantry and don’t want to miss it. In our case, the freezer would also go in there.
The idea was rather the other way around: guests downstairs and private upstairs, just for us. The large office serves as an office for one of us but should also be usable by both on weekends (if, for example, one is working/playing on the PC and the other can lie down on a couch there and read). Also, it should allow the possibility to move a beanbag under the windows into the sun.
In general, it should be considered to reduce the storage room on the ground floor and give more space to the living room; the approach is understandable, and we will sleep on it a few more times. On the other hand, what is, in your experience, the middle ground between an overly large open space and wasted space and being too cramped? We are also aware that you can’t place a book wall in the living room because there is simply too little wall space for furniture (also due to the windows). We have seen criticism in other threads in this regard.
We discussed and rejected the cellar issue because, in the end, you might save about 8 sqm of storage space on the ground floor and 10 sqm upstairs, as well as the pantry and the technical room on the ground floor. What would a partial cellar cost? (not living space quality) The extensions we want (house lengthening) cost about 35k. A partial cellar for 50 sqm will certainly be more expensive, no question. But it also brings more square meters. Following your advice, we asked the project manager again, and he sees the partial cellar as not optimal since, in the worst case, a floor slab still has to be laid across the entire cellar area, and it then doesn't pay off financially. He estimates a full cellar (no living space quality) would cost about 100k – which does not make sense for us because we really don’t need the space.
The large office came about because, as described above, other uses would be desirable (catching some winter sun when the sun has already disappeared behind the hedges on the ground floor).
Please find attached the wording from the development plan – which is clear in my opinion. None of the other approximately 100 builders received an exemption to place the garage on the boundary either. (To be honest, I can understand the municipality's point, it looks more open. It is naturally disadvantageous when one (like us) has a narrower plot.) A wooden garden shed may be placed on the boundary, nothing more.
We also have neighbors to the north. Indeed, 4m is not enough, and there won’t be a fully functional double garage. As described above, the widening of the plot towards the back might bring it to maybe 4.5–5m. Hopefully, that will be enough for a comfortable single garage.
An office with glass doors would be worth considering, thanks for the hint. Do you have any ideas for implementing windows in the wall? Or examples of realizations?
