ᐅ Main drainage pipes beneath the foundation slab

Created on: 19 Mar 2026 17:20
P
Pathe
P
Pathe
19 Mar 2026 17:20
Hello dear forum users,

I have attached a soil pipe plan and have some questions about it. I hope to receive helpful answers.

We received the following plan from our builder. I have added some measurements for reference. The blue circle indicates the soil stack from the upper floor. The vent pipe is routed through the roof there.

From my research, the main drain (soil pipe) is quite long, and I am concerned that the kitchen (on the far right) might face drainage issues.

Due to the upper floor layout, there is no real possibility to install an additional vent pipe through the roof at the end of the branch.

How would experts assess this situation overall?
Y
ypg
19 Mar 2026 18:33
Then why not show the drawing?
P
Pathe
19 Mar 2026 19:54
Hey,

sorry, it seems the attachment didn’t come through properly.

Y
ypg
19 Mar 2026 20:51
Ok.. by the way, there are very few experts here, almost everyone is a homeowner.

Basically, you can do it like this. The building services engineer will offer you the shortest, and therefore most cost-effective, pipe routes, which in this case are under the house, so a basement pipe duct.

Where is the wastewater shaft located? What is the space under the stairs?

For us, it was a while ago, but as far as I remember, the toilet, technical room, and kitchen were planned to connect directly to the outside, then combined around and in front of the house. The top priority: keep as few pipes as possible under the house if you want to maintain control.

This may mean a few extra meters and a bit more money, but it is more sensible and practical for any future work on the plumbing.
Knöpfchen19 Mar 2026 21:32
Indeed, the section of the drain pipe from the downpipe to the kitchen is actually quite long without ventilation.
If you do experience issues, you have the option to retroactively install a vacuum breaker vent on the external soil stack; planting a small shrub nearby can help hide it. 🤗
Another consideration could be a drain for condensate as well as a drain for emptying the heating system, both inside and outside for a heat pump.
A utility sink in the technical room can also be very useful for mops and similar cleaning tools.
Y
ypg
19 Mar 2026 22:21
Knöpfchen schrieb:
A utility sink in the technical room can also be very useful for mops and similar items.

With just over 4 meters (13 feet), there is hardly any room to move, let alone handle a mop..!