New foul drain to an existing room

[RayB]

Apologies for asking for help with what must be a common issue but for which I don’t seem to be able to find an answer anywhere.
 

I am wanting to add a toilet (DIY) to a ground floor room that has no sewer provision. The property is a bungalow with strip foundations and uninsulated concrete floors. Property build late 1970s. The property is on a septic tank. I am planning to run a new drain to the existing manhole which has an invert level of apx 1200m, which has an unused connection in the right orientation. What I can’t workout is how to get the sewer outside? Is is standard practice to tunnel under the existing foundations ie drop vertically inside the property to get appropriate depth? The toilet will be on the external wall nearest to the manhole. I was planning to dig out the floor of the room to add insulation so happy to do this. My main concern is undermining my existing foundations as a deep hole would be required either side of the wall, and keeping the BCO happy with the plan.

 

Any advice would be greatly appreciated.

 

Many thanks in advance,

 

Ray

[Russell griffiths]

You do it two ways either dig shallow and go over the concrete footings or dig deep and go below them. 
 

dictated by a few things. 
depth of concrete

invert level at house, working backwards from septic. 
 

if your invert level on the pipe at the toilet end is deep, I think building regs say 1m ( check this ) so when you flush the poop goes down with a whoosh you will need air admittance to stop the whoosh pulling water from the traps in the room. 
 

I would start by planning where the toilet is going and marking location 

then dig the floor out, expose bricks below dpc on the inside and outside 

then stand back and have a good look, if you can go over the concrete and below dpc then that’s cool. 
 

or if your toilet is on the outside wall you can just cut a hole in the wall going out into a junction into a small vertical soil stack. 
 

lots of ways to do this really 

better off with a couple of pictures and a diagram, including other vent pipes on the system. 

[saveasteading]

1 hour ago, RayB said:

The toilet will be on the external wall nearest to the manhole. 

So horizontal is easiest, but slightly ugly externally. 

There's every chance you can go down before turning out, without reaching the footing. Big hole outside will prove where the footing is before committing to the fiddly work inside.

[Redbeard]

2 hours ago, Russell griffiths said:

or if your toilet is on the outside wall you can just cut a hole in the wall going out into a junction into a small vertical soil stack. 
 

 

Glad you said this, @Russell griffiths. It's the first thing I thought of, which avoids loads of complication AFAICS, but I wondered what I was missing. Am I right, however, in remembering that Durgo valves have to be inside?

[Gone West]

3 minutes ago, Redbeard said:

Am I right, however, in remembering that Durgo valves have to be inside?

You can buy external AAVs.

 

https://www.floplast.co.uk/product/external-air-admittance-valve

 

 

[RayB]

Fab, thank for all the advice. I’ll post some photos once I start the excavations, which won’t be for a while, but now having a direction of travel helps. I fear there are only two courses of bricks between the foundations and the dpc, so the only options are out and down or down and out.