Foul water under slab

[Ben100]

Hi All,

 

I have a question on foul water pipe running through a slab. The issue I have is that the existing external drain I'm trying to connect to is quite shallow and I'm also digging down in the extension to lower the floor level. These two points mean that I don't have a lot of drop to run my new foul water pipes.

 

Because of the shallow drop issue I'm trying to run the pipes along the shortest distance and at a drop of 1:80. I believe 1:80 should be fine as I have 4 toilets, 3 showers, 1 bath and a kitchen going through the pipe, so lots of flow.

 

The issue I have running the pipe through the house is that at it's highest level it will run in the concrete slab, with 10cm concrete and 6cm screen above it. The pipe will then descend through the slab into the insulation and then into the hardcore layer before connecting to the external drain. The runs are mainly straight with the ability to rod.

 

I'm not sure if this is allowed, not recommended, or just a bad idea...?

 

Cheers,

Ben

[PeterW]

No issue with it but I would make sure that junction is fully roddable or run a spine from the back corner of your larder direct to the manhole and then fishbone into that all the way down as that is a serious change of direction !

[Mr Punter]

I am not sure what the right angle is for. I would have 2 straight runs - 1 from utility to manhole - picking up the WC en route and 1 from kitchen to manhole. I would want access to the start of each run for rodding / jetting. This means you will not need an inspection chamber in the kitchen and the runs will be a fair bit shorter.

[Ben100]

Thanks, that's good to hear this is possible!

 

The reason for the right angle is that this is an extension, not a new build, so there is no direct route from the utility room to the manhole without digging under the existing house.

 

I should be able to replace the right angle with a more gentle curve or 2 45 degree angles with spacing. I can then add in rodding access at the ends.

[Ben100]

On a related topic, would you bed the pipe in shingle or encase in concrete? I’ve also read a gap should be left around the pipe when going through the foundations?