Urgent help needed to join sewer pipes

TACH Forum, I urgently need help, we are building an extension onto our existing single-family house and are converting it into a two-family house, for which we need to reroute the sewer pipes located on our property. Our pipe is currently a DN 160 pipe, and so is the neighbor’s (also a two-family house). Now we thought since both pipes have to be laid, we could combine them. What size pipe would it then have to be? From the gut feeling, I would say a DN 250 would have to be laid. What do you think???

I think the DN160 should be completely sufficient. An increase inevitably leads to a significant rise in the amount of water needed to transport the feces. A too large cross-section is just as bad as a too small one. A friend of mine built a six-family house with about 700 sqm last year. The connection was a 160 pipe.

Hello,

Two houses with 2 apartments each on one main sewer line? Technically no problem, but if a clog occurs ...... which house will bear the costs?
I would definitely discuss the shared sewer line with the municipality's wastewater department. Should one of the two main lines be connected to the municipal sewer, or should a completely new line be installed? Is there a so-called separate system in the municipality or in the street (rainwater and wastewater are each discharged separately)? I think in any case a permit from the municipality is necessary (observe the drainage regulations).

If it is permissible, a manhole should definitely be constructed at the junction point of the two lines.

Good success

I would not connect the two houses to a sewage pipe. Because, as already mentioned, who ultimately will be responsible for clearing a blockage? Imagine if the neighbor is the cause but has no money for the cleaning; then it all falls on you even though it's not your fault. And if a shaft is constructed, on which property should it then be built? Someone ultimately ends up with the short end of the stick. Furthermore, one of the connections leading to the public sewer must also be closed.

There are clear specifications for the diameters of the pipes from the municipality or the DIN standard. So that should not be your task; the municipality must determine that. However, 250 is usually too large because sometimes only 200 pipes are laid in the street sewers (max. 300). Basically, combining a sewer (as long as the municipality/city agrees) is not a problem. A sewer does not clog that quickly, and a simple cleaning does not cost so much that it would make you poor. And you already save the money for 1-2 cleanings now by combining, so that would not be a reason for me. You should definitely install an inspection shaft, and it will probably even be required. Of course, it has to be on the property, but if you place it in a reasonable spot, then it is not really a restriction on the property. If someone doesn't want to see it at all, they can put it in the driveway and pave over it (but of course that is a lot of effort if you ever need to get to it). Keep in mind that in almost all municipalities/cities, an approval of the sewer pipe is mandatory. So only cover with sand and earth again after an employee of the public service has inspected it.