Window height / Venetian blind box

At 250 height you must/should install aluminum windows. Everything else will cause problems in the long run.

Yes, that really seemed to be a challenge. But the window supplier sees it as no problem since the sash is only 1m wide.
Additionally, he designs the windows as balcony doors but said that apart from sturdier fittings there is no difference to a window. He only insisted on gluing the panes to the frame.

The boxes are all 30cm. The problem is that at 250 height the "package" of the slats also needs a lot of space in the box. If you even find 25cm high boxes somewhere, your slats won't fit in and will be visible when raised. Personally, I would find that annoying...

I would find that annoying too and your statement supports the feeling that it fundamentally can't be narrower.

What clear room height will you have?

275cm from finished floor level was planned.

10cm floor build-up? That little? What does your floor build-up look like? What insulation do you have? Our floor build-up is 15cm (1.5 tile, 5cm screed, 2.5cm tacker board, 6cm insulation) although we have 12cm XPS under the floor slab...

The basement is built on existing structure, the 12cm insulation doesn’t count somehow, for whatever reason. The zero line was set above that.

I think I will have to bite the bullet and reduce the window height. It just feels a bit stupid since the tall windows were really important to me and that’s why I was okay with the smaller width. (Yes, they are not really small now..)

Best regards

Am I mistaken in the impression that your house is being very much "on the run" "planned"?

Well, as a layperson in construction, you see drawings with measurements and think, we have discussed everything important, the rest they will know how to implement.
I think one cannot expect a non-construction expert to know how high roller shutter boxes should be at which window height.

Over time you learn more and question things more critically. Whether the initial planning was not good... no idea, I think it was, since there have already been some adjustments, but I really can't judge that.
The roller shutters were planned in the ground floor from the start, so no last-minute change on our part.

I also find 10cm floor construction quite little. You should also discuss the transition from floor to window. Floor-to-ceiling windows do not necessarily mean threshold-free (which many people want).

Fortunately, I found out relatively early (by asking) that floor-to-ceiling does not mean flat threshold. The ones for stepping out we have designed with a flat threshold. But thank you for the hint.

I think I will have to swallow the toad and reduce the window height. It just feels sort of stupid because high windows have always been really important to me and that's why I was fine with the smaller width. (Yes, they aren't really small now..)

I understand that too. Higher rooms and tall windows were important to me as well. We have 270 clear height and 240 high windows + 30mm venetian blind boxes. The structural carpenter made a flush lintel, the boxes (Beck and Heun) come as mounting boxes directly on the windows. Sounds all nice and good. Unfortunately, we have a huge problem with the window supplier, the delivery dates are constantly being postponed...

Well, as a construction layman you look at drawings with measurements and think, we have discussed all the important things, the rest they will surely know how to implement. I think you can’t expect a non-construction professional to know how high Venetian blind boxes should be for which window height. Over time you learn and question things more critically. Whether the initial planning wasn’t good... no idea, I think it was, since there have already been some adjustments, but I can’t really judge that.

As a construction layman, you wisely discuss your project as a whole in such a forum with a lot of people who find overview and insight amidst the confusion of drawings and measurements instead of in umpteen single threads (each again about only one little aspect). And you get a planner for the whole project. On the other hand, if you have to only start studying smartly about each trade as it comes up and are pointed out principle differences of alternatives A/B/C by the specialist dealer, you’ll get many gray hairs and never stop being amazed (which is not a feature, but a bug).

The Venetian blinds were planned on the ground floor from the start, so no last-minute switch on our part.

In the end, it doesn’t make much difference whether you fall short in the planning itself or in understanding why things were planned that way.