Water on flat garage roof problematic/dangerous?

Editing is unfortunately no longer possible. I still wanted to post the complete response from the GU here:

"The construction of the flat roof is not yet completed. The lower edge of the drain of the garage roof is, to date, above the current water-bearing layer. This drainage element is a finished part and therefore cannot be installed deeper due to construction design. Therefore, water currently remains standing on the flat roof. Since the garage roof receives a gravel covering, additional protective mats (made of rubber) will be applied to the waterproofing to protect the waterproofing. These mats raise the water-bearing layer and thus largely prevent standing water. The remaining standing water on the waterproofing afterwards does not constitute a defect according to flat roof guidelines, but rather cannot be completely avoided due to connection details, component overlaps, dimensional tolerances, etc."

Regards Christian

well look... then let him finish it properly. And if there is too much on it, you can still complain. There was hardly anything on ours, but now we have grassed it anyway. Neighbors opposite deliberately have no drainage - for cooling. Uh no comment.

otherwise roof greening

This drain element is a finished part, and therefore cannot be installed deeper due to design constraints.

However, the assembly instructions do not say "choose a product from our range intended for a different purpose or install a suitable product the wrong way around". I do not believe that a drainage system inventor would design a drain that guarantees residual moisture on the garage roof – unless the model is specifically intended for a green roof and is supposed to take into account that grass is less suitable for conventional hydroponics. An unplanted roof is not supposed to become a moss-covered roof, so zero-residual drains are used for that.

"additional building protection mats (made of rubber) are applied to the waterproofing for the protection of the waterproofing. These mats increase the water-bearing layer and thus largely prevent standing water"

I will translate: the water will then stand between the roof layer and the building protection mat in the future.

For all puddles, the rule is: it doesn't matter in summer, but in winter it freezes, expands, and gradually destroys the surface of the roof. The drainage is simply too high; the reason "it can't be installed deeper" is a joke. Ask him if he really can't do it and whether you seriously have to get someone else who can.

PS. and what is the gap between the pipe and the roof supposed to be? Is it sealed or does everything flow past the pipe there? The roof waterproofing belongs inside the pipe, not the other way around.

The roof sealing belongs inside the pipe and not the other way around.

A truth - in our world. But the executing contractor apparently has no (or an esoteric) understanding of physics