We have 3 large sliding doors from the living/dining/kitchen area to the terrace. The terrace is partially enclosed by a balcony (with its own drainage). One door is secured under the balcony, 2 doors are not closed. The terrace must be connected barrier-free.
Do I need a drainage channel only in front of the 2 unclosed sliding doors or also at the closed sliding door?
According to the regulations for unclosed ones, yes.
For closed ones, it depends on how they are closed.
Individually you can coordinate everything if you don't want a gutter. But then don't whine if there are problems.
The gutter must be 15 cm wide.