Water on flat roof - double layers of roof sealing

Hello,

on our side extensions (garage), we have standing water for an extended period (24-36 hours) after rain showers. I estimate 5 cm, I plan to get up on the roof soon.
The builder says that with a flat roof this is completely permissible or even good because of the waterproofing. I'm having a hard time with that ops:

I remember your builder as a serious and competent partner - are you sure that there is actually 5 cm of water standing? Our eyes like to play tricks on us now and then.

If that should prove true, it would probably mean that the required slope of 2% on the flat roof was not executed correctly ... assuming, of course, the drains are not the cause; that is, clogged with leaves.

Rhenish regards

Hi construction expert,

yes, for me it means up on the roof with the spirit level. I hope it's not 5 cm. In the meantime, we had a good conversation. I will report.

So water stands about 1.5 - 2 cm.....

The roof also has a minimal slope. However, only up to the corner where the gutter is installed. There the roof becomes level again. Therefore, these remaining 1.5 cm can never drain.

It is a bit comparable to a shower tray (I hope you understand).

Now, of course, the question is harmful yes or no.....

How big is the puddle? I think it’s probably harmless, BUT I’m not a roofer either.

We also have small areas roughly 20x80cm where about a centimeter of water stays standing.

I have to measure again. But it is more like 3 * 3 meters. Basically a flat shower tray............

upDate:

Water is between 0.7-1 cm....

The roof insulation makes everything look a bit different.

Now the question is whether to take action or not. I have always learned that water finds its way... But it could also be that everything above is sealed.