ᐅ Sewer Manhole Backup – Backwater Valve?

Hello housebuilding forum,

So far, I have avoided posting, but with my current question, I would like to clearly describe the situation here.

We have added an extension to our single-family house and are already quite far along (currently plastering is underway). In the extension, a new bathroom was planned and built.
The wastewater from the bathroom flows into our combined sewer system (our town only has combined sewer systems).
After the bathroom wastewater, rainwater is also fed in, and then it goes directly to the sewer shaft at the street. My architect tells me that I need a double backwater valve between the bathroom and the rainwater in the underground drainage pipe.
However, my bathroom is located above the backwater level at the street, so I usually read that it is not necessary to install a backwater valve, especially since, if required, it would have to be an electric one, which would of course be more costly.

I basically have no problem installing a backwater valve... but if, aside from a blockage in my underground drainage pipe, it doesn’t make sense, I don’t see the necessity.

A brief illustration of the location:

O (Sewer shaft) Shaft cover is still 35cm (14 inches) below the finished floor level of the bathroom
|
|
|
|
________L (Rainwater inlet)
.................|
.................| (This is where my architect wants to install a double backwater valve)
.................L (Bathroom)

I hope my question is clear enough.

Regards, Anbauer2019

Hello again.
Doesn't anyone have an opinion or advice for me?

Anbauer2019 schrieb:

Doesn’t anyone have an opinion?

I could imagine that your 1980s computer graphics, so to speak, "don’t exactly come across clearly to most people right away."

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https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/

11ant schrieb:

I could imagine that your 1980s-style computer graphics, so to speak, "don’t exactly immediately resonate with the majority."

Hello, okay, I understand. I deliberately did not upload a drawing or even the wastewater plan because I hardly see posts with drawings here (which are still normally answered). I had assumed that mentioning the backwater level BELOW the bathroom floor height would be sufficient. But no problem, I can gladly present it more clearly.

Perhaps a simple image created with Paint is not ideal, but I would rather not use the official underground piping plan.
I hope this makes my question easier to understand.

Hello

Since the backflow level is below the bathroom drains, I don’t see any need for a backwater valve here. To prevent backflow in case of a blockage and to have an additional inspection and cleaning opening, I would suggest installing a small shaft in front of the bathroom.

Olli

wrobel schrieb:

Hello,

Since the backflow level is below the bathroom drains, I don’t see any need for a backwater valve here.
To prevent backflow in case of a blockage and to have an additional access and cleanout point, I would recommend installing a small inspection chamber before the bathroom drains.

Olli

Hi Wrobel, thanks for your reply. That’s also the only information I’ve been able to find during my research so far. I have to say that my architect hasn’t been the best fit for us, so I wanted to bring this topic to the forum for advice.

The idea of an access and cleanout point sounds good. What would you recommend for that? When I search online, I see, for example, DN110 (4 inch) pipes with DN400 (16 inch) chambers. A basic question: are these chambers sealed and odor-tight? Does anyone have experience with this? It would be located near our terrace.