Covering shallow sewer pipe under concrete Patio

[DIwhYdidIstartThis]

Hello all,

I’m replacing a concrete paving slab patio in the back yard. The original patio used 50mm deep concrete slabs on hardcore & sand. I’m planning to pour a 100mm deep concrete patio on 100mm hardcore. In order to achieve the same final height to line up with the rest of the patio, I have to dig down an additional 50mm into the existing hardcore to accommodate the additional concrete.

However, when I removed the original 50mm slabs and started to dig the hardcore, I found a 4” sewer pipe just under the surface of the hardcore, sloping downwards form the boundary wall to the neighbour's house. I mention sewer pipe but this is likely the drain for the neighbour's kitchen sink, dishwasher & washing machine waste-pipes as it eventually runs alongside my own drain for the same purpose.

However, it seems much shallower than I expected. For me to pour my own new concrete patio it looks like I could be pouring directly onto the exposed pipe at the boundary wall. The patio is going to take some weight as I’m planning to pour this as if it were a new floor for a future extension.

I’m worried due to the shallow nature of the pipe that the weight of the new patio may damage it. As the pipe comes through the wall the underside likely rests on a block so that would be a pressure point.

There will be no chance to dig this up once the concrete is poured.




Questions are:

1. Is there any regulation to specify a minimum depth for such pipes (This is a 3 year old build in a new estate)?
2. Does it seem strange that the a pipe from another property has been routed through my own?
3. It would seem that this shortsightedness will limit what I can do in my own property. However, I'm too far into the project now to change. Are there any recommendations to protect this pipe in any way?

Thanks and advance for the suggestions.

 

[DIwhYdidIstartThis]

Adding picture of pipe coming from from wall to neighbours property:

Another picture of pipe running parallel to kitchen waste pipe from my own property:

 

[Ben-gee]

You need to find out for certain what this pipe is used for- not just guessing.
Then, if it were me I would re-route it so that it would be outside the area of my proposed extension.
( I wouldn’t bother if it was used as a conduit for cables for instance)

 

[DIwhYdidIstartThis]

You need to find out for certain what this pipe is used for- not just guessing.
Then, if it were me I would re-route it so that it would be outside the area of my proposed extension.
( I wouldn’t bother if it was used as a conduit for cables for instance)

Hi Ben-gee,

Thanks for your response. I can't say for sure because none of the pipework in my neighbour's house are exposed but it definitely isn't used for cables and the pipe runs alongside my own one that is definitely used for grey water. There is also a rain water gully just to the other side of the wall that is likely connected to it. I have added a diagram with orange lines showing pipes I have access to and dotted lines showing my best guess as to what is going on:

I'm not sure what the correct terminology is for those access drains on the right but they are the sealed black drain covers atfor a 90 degree turn to route the drains out to the street.
Rerouting it around the slab seems like a big job. If it is already this shallow then wouldn't adding another 4-5m affect the fall too much?
No matter what I do, some part of it will be under the concrete slab / floor. I'm wondering if there is some regulation that states a minimum depth. If so, and this pipe is too shallow, maybe I can go back to the builder and get him to reroute it properly.

I appreciate any and all input.

 

[Ben-gee]

As it’s new build I’m surprised that the rain water seems to be combined with the waste?
Round here they would definitely be looking at disposing of rain water to a soak away, to relieve pressure on our overworked sewerage system.
That’s why I say you need to establish exactly what goes where, don’t assume anything!
How deep are the pipes when you look inside the two man-holes?

 

[DIwhYdidIstartThis]

As it’s new build I’m surprised that the rain water seems to be combined with the waste?
Round here they would definitely be looking at disposing of rain water to a soak away, to relieve pressure on our overworked sewerage system.
That’s why I say you need to establish exactly what goes where, don’t assume anything!
How deep are the pipes when you look inside the two man-holes?

Thanks. I'll take a measurement tomorrow and come back to you.
In the meantime, with regard to my original picture, does that pipe at the wall seem a bit shallow? Is there a minimum regulated depth it should be below the surface?

 

[DIwhYdidIstartThis]

Thanks. I'll take a measurement tomorrow and come back to you.
In the meantime, with regard to my original picture, does that pipe at the wall seem a bit shallow? Is there a minimum regulated depth it should be below the surface?

Coming back with measurements, tops of the pipes are 20cm from the top of the manholes. I also did some tests with the neighbour when we had them opened. You were indeed correct in that the rainwater and greywater are not mixed.
Although the pipe from my house is definitely the grey water drain, the pipe from the neighbours house that runs alongside my own seems to be only connected to the rainwater gully.
I'm a bit confused then why, if their grey water is piped via an alternative route (probably under the house), why wouldn't their grey water be piped via the same route?
Does it seem strange that the builder would pipe the rain water only form the neighbour under my patio alongside my greywater drain?
Is there a minimum regulated depth it should be below the surface?

Thanks for the help