Drainage plan for extension

[JimExtension]

Hi, I'm trying to self plan a rear extension to our semi-detached house, and hoping someone could give some feedback on my drainage plan.

Currently the rain water pipe (RWP), and soil vent pipe (SVP) connect to a manhole at the rear of the property. This is a private drain, that then runs into the neighbour's garden where it becomes a public sewer, before heading off to the street sewer.

We're planning a rear kitchen extension which goes over the manhole / SVP / RWP. Additionally the old kitchen will turn into a toilet / shower room.

My plan, as shown on the attached images, is to
- keep the existing manhole (change to a sealed cover) - I believe this is allowed as this is a private drain.
- for easy maintenance add a rodding point in a straight line to this manhole, outside of the extension.
- create an additional manhole at the side where the new toilet/shower room and re-routed RWP can connect into. This new manhole will connect to the old manhole under the extension.
- leave the existing SVP within the extension, but boxed in. I believe moving it would require a lot of work to the bathrooms on the 1st and 2nd floors to re-route pipes, which I'm keen to avoid.

How's this look? Is this anywhere near sensible - is there anything I've missed? Thank you

 

[George_engineer]

No.

If you must have a drain/sewer under your extension, take it to a MH on one side then run it straight through to a MH on the other side. Avoid internal MHs at (almost) all costs. I would only countenance one in a garage, not even in a utility.

Relocate the existing SVP - either completely or by running it laterally at higher level (consider access and rodding points)

 

[^woody^]

No.

If you must have a drain/sewer under your extension, take it to a MH on one side then run it straight through to a MH on the other side. Avoid internal MHs at (almost) all costs. I would only countenance one in a garage, not even in a utility.

Relocate the existing SVP - either completely or by running it laterally at higher level (consider access and rodding points)

View attachment 308679

What's the m/h on the right of the extension doing?

 

[George_engineer]

What's the m/h on the right of the extension doing?

Ideally you have an IC at the point it leaves your property. It also allows the new pipe to be laid to a consistent gradient. Trying to tap it into the existing pipework may create an unintended change in gradient mid-run.

 

[JimExtension]

Thanks for the replies.

If the SVP is moved to the side and routed to the manhole on the left does that make the underground pipe bend too sharp?

It looks like it would have to go through a tight bend at the manhole.

 

[George_engineer]

You can get a 45 degree bend just before entering a IC then allow 90 degrees in the IC itself. It is not ideal but it is a workable solution. See the diagram on this page (the bible) https://www.pavingexpert.com/drain05

Other option is to run it to the downflow IC on the right hand side of the extension.

 

[JimExtension]

On the right side I think the gap between the extension and boundary will only be 40-50cm, so not enough room for an IC?
But perhaps big enough for a rodding eye?

 

[JimExtension]

On one of the above comments it says "Relocate the existing SVP - either completely or by running it laterally at higher level".
For the "running it laterally at a higher level" option, would the following be acceptable - see diagram?

There is now a lateral bend below the 1st floor bathroom - this could either be above the extension roof, or could be below it. This then joins into the new soil pipe ground level location as suggested by @George_engineer

Thank you.

 

[^woody^]

On the right side I think the gap between the extension and boundary will only be 40-50cm, so not enough room for an IC?
But perhaps big enough for a rodding eye?

That chamber on the right of the extension is actually optional, not essential.

 

[Murdochcat]

Maybe put a called into your local building control for their views before you do anything

 

[^woody^]

On one of the above comments it says "Relocate the existing SVP - either completely or by running it laterally at higher level".
For the "running it laterally at a higher level" option, would the following be acceptable - see diagram?

There is now a lateral bend below the 1st floor bathroom - this could either be above the extension roof, or could be below it. This then joins into the new soil pipe ground level location as suggested by @George_engineer

Thank you.

Not really.

Put the stack on the side elevation, and if you can't take the pipes out the side elevation too, then bring them out the rear elevation and bend them around the corner.

Also, you are unlikely to be able to put a rainwater pipe into the fowl water drain. You could keep existing, but if you are adapting drains then the inspector may want them separating.