Is a rain gutter below the terrace window necessary?

Hello,

I am currently planning the construction of our terrace. We want to design the terrace along the three floor-to-ceiling window elements.
I recently walked through the new development area and looked at how other builders have implemented it.
Many have no drainage at all, some only have one drain directly on the masonry (almost between the windows), and others again directly below the windows.
In the red marked areas there would be space for a rain gutter. I could drain the outer two directly over the downpipes.
Is that sensible (do you possibly need a trap for odors if the rainwater is temporarily stored in a cistern)?

Looking forward to your ideas, many thanks in advance.

Best regards
Julian

What does your architect or landscape gardener say about that? They have to guarantee it in case of doubt.

We asked our construction company about this again. In principle, windows with a flat threshold probably need a drainage. We have a roller layer made of facing bricks in front of it and attach the terrace below the roller layer. According to the construction company's statement, then one is not needed. He said, "if the water is that high, we have completely different problems" :D

We have a ground-level entrance, so it would make sense to install a drainage channel. The architect is no longer reachable because the construction has already been handed over and he has since retired. The landscaper said it is not necessary, although I would rather play it safe.

What is your experience regarding connecting a drainage channel to the rainwater system, which has a cistern attached (with respect to odor development)?

Many have no drainage at all, some only have drainage directly on the masonry (basically between the windows), and others directly below the windows. There would be space for a gutter in the red-marked areas. I could drain the two outer ones directly over the downspouts.

The question is what kind of terrace you want. For a stone terrace with ground-level exit = yes, install a drainage channel. Wooden terrace/WPC = no, do not install a drainage channel (this does not comply with the standard but is a pragmatic and well-functioning solution).