Change of the size of roof windows after building permit

From which rafter spacing is the 94 cm derived?

I really can't say, I wasn't working in the roof window sector. If the nominal size refers to the rough opening between the rafters, it would be about 110 cm. In general, the rafter spacing has increased, since the rafter cross-sections have also changed in connection with the insulation thickness. Forty years ago, 80 cm rafter spacing was still largely common and, except for very narrow double casement windows, almost the rule to require replacements.

could one maybe remove a rafter and flange on,

Flange on??? - what, to what?

Attach??? - what, where?

That means you take out a part of the rafter and place a slightly longer one next to this free space. This way you gain the width of the rafter (about 6 cm in my case). See picture "Rafter spacing slightly too narrow"

I would have also seen it as a kind of "change," but the sketch is quite revealing about the different types.

Without counter-bracing that clamps this auxiliary rafter, it seems like a botched construction to me. Warping is practically inevitable. This might work in glued laminated timber, but in solid wood, it’s a joke.

Without bracing that clamps these auxiliary rafters, this seems to me like a botched construction. Warping is practically guaranteed. It might still work with glued laminated timber, but with solid wood it's a joke.

You're probably right. I think there are only 2 options: a proper beam or trying to space the rafters a few centimeters further apart – if the structural engineering and the carpenter allow it.

You are probably right.

And if not, I strongly believe it anyway ,-)

I think there are only 2 possibilities: a proper change or trying to set the rafters a few centimeters further apart

Forget it, it’s not necessary. I just checked in . No extra width is needed, the double casement windows are all just supplementary, even at the staircase it is sufficient. If anything, then only install a wider* one there – but so that it can be cleaned from the gallery. In the floor plan, the double casement windows seem to me to fit in width between two rafters – but not placed between rafters in terms of rhythm. That means I expect a need for adjustment here, then move them into the next bay towards the interior of the room.

*) or taller: it only needs to reach exactly to the 2 m line at the top.