Soil stack and underground drain advice please!

[SimonD]

I've been putting this last bit of drainage off for quite some time, but I can't ignore it any longer and need to find a solution (because I want to install our heatpump along this wall during August!). In the image below you'll see what is a temporary plastic drain pipe with connected soil pipe which serves 110mm drain from a bathroom upstairs. This was a clay installation but we found it to be cracked and damaged, so I just riped it out and put this temporary stuff in there.

 

The clay gully lying on the ground was previously at the end of the run which goes approximately 3m along the wall behind the camera.

 

Now I need to extend the drain for the first fix of the final bathroom to go in and heatpump. My problem is that as you can see, the drain is very shallow and previously the clay pipe was only about 20mm below ground level with the gully raised up a bit (I don't think I can get away with that now with BC?) and I don't want to increase the ground level too much due to the wood fibre ewi. The current plastic drain is at a steeper gradient than the remaining clay pipe it's connected to so I do have so wiggle room.

 

I've considered whether I just run a 110mm waste from the bathroom along the wall to the soil stack but by the time I've got suitable fall, it's very unlikely to be over the min 450mm to invert. But this would be ugly and I also want to keep this wall free so I can get the heatpump as close to the wall as possible (whether this is the best place for the heatpump is another question as I can put it at the front of the house instead but that has complications too!)

 

So main question is whether it's possible to get a soil stack to drain tee that allows me to extend the drain as needed where I would put in a direct connection to wc and a gully maybe just 1.5-2m beyond this soild stack, or is this a stupid design idea? And yes I know this should have all been considered at the design stage but I was totally wet behind the ears then and trusted our architect to consider these things only to find he put almost all rooms needing drainage in stupid places compared to the existing drains! We have no options to dig out any of the drainage is the drain travels under the retaining wall you can see in the photo and then 8m further into the hill to meet the mains sewer that serves the whole row of houses. 

 

Any ideas and suggestions please?

 

 

 

[twice round the block]

The first thing I would do is replace your 90 ° bend with a 90° T and put a roding point on it where your old gully is laying.

As dropping waste from height may not clear the bend.

[SimonD]

53 minutes ago, twice round the block said:

The first thing I would do is replace your 90 ° bend with a 90° T and put a roding point on it where your old gully is laying.

As dropping waste from height may not clear the bend.

 

That was my original thought, but maybe incorrectly, I had this nagging idea that soil stacks are supposed to be connected using a rest bend and wanted to confirm if it's okay to use a tee for the very reason you say. The old drain was literally full of shit and I had to rod it and use my pressure washer drain attachment on a regular basis until we started the project - I really don't want that risk again.

[Mr Punter]

11 minutes ago, SimonD said:

I had this nagging idea that soil stacks are supposed to be connected using a rest bend

 

Yes you need a rest bend.  You could also have an access to the stack about 1m up in case it gets blocked.  You could have a small inspection chamber downstream on the underground if you need to connect other pipes.

[Conor]

Deffo stick an inspection chamber downstream of the rest bend. You'll need to cover the pipe in concrete to keep BC happy.

[Nickfromwales]

T not allowed as the change of direction at the base of a stack, unless it’s above the rest bend, so you can add a 110mm connector which has the rodding access on it, then have the rest bend.

 

[SimonD]

41 minutes ago, Mr Punter said:

You could have a small inspection chamber downstream on the underground if you need to connect other pipes.

 

Ah, yes. I could then connect the drain to go to the bathroom at the inspection chamber 

 

42 minutes ago, Conor said:

You'll need to cover the pipe in concrete to keep BC happy.

 

That's what I feared!

 

Thanks all, that's given me a plan!

[Nickfromwales]

Ask BCO what they’ll accept as a pragmatic solution regarding how much (little) concrete cover you can get/have to get in place. 

[kandgmitchell]

Given the location of the drain run which seems to be between the retaining wall and the house, I can't see a BCO having any issue with limited concrete cover. You could haunch it up if need be but that may look a bit ugly.

[SimonD]

16 hours ago, Nickfromwales said:

Ask BCO what they’ll accept as a pragmatic solution regarding how much (little) concrete cover you can get/have to get in place. 

 

15 hours ago, kandgmitchell said:

Given the location of the drain run which seems to be between the retaining wall and the house, I can't see a BCO having any issue with limited concrete cover. You could haunch it up if need be but that may look a bit ugly.

 

Thanks, it's always a good reminder to speak to BCO before embarking on a plan. Given how long it's been, I think I recall sensibly installing eps ewi at about 300mm all along the bottom of the woodfibre for splash protection so would just need to make sure I've got something like 150mm wide strip of pea gravel between hard surface and the ewi. I can alway put pavers over and concrete to make it look nice. At least this bit of the house is rarely accessed so it doesn't matter a whole load if it looks a bit weird.