Odor trap for flat roof inlet

Hello everyone,

we are currently building a roof terrace on our flat roof. It is noticeable that there is a "sewer smell" coming from the roof drain. Is there any valve insert or similar that can be retrofitted into the pipe? It should be a standard 100 mm KG pipe.

The alternative would be to break open the wall on the ground floor and install a siphon there, but that is a lot of effort...

Why channel? Have you connected your roof terrace to the sewage system?

Yes, the rainwater from the flat roof flows (together with other connections such as kitchen / bathroom / WC) into the wastewater. It is difficult to change that afterwards, it should have been done 40 years ago... ;-) The fact that the flat roof can and should be used as a roof terrace was not planned back then.

That would be forbidden for us.

Aha, why is that? What is the background? As mentioned, it has been like this for the last 40 years (toitoitoi!), but if it is forbidden, there must be some reason for it... Possibly the ammonia that can damage the seal of the flat roof?

There are cities/municipalities that do not have separate black and grey water systems.

Where there is only one common sewer, only that one can be used. And where there are two, they should also be properly connected.