What’s the max length on a horizontal soil pipe with new connection going into a drain

[Piperdave22]

As above really what’s the max length a soil stack can be run horizontally, it will be feeding a toilet and a basin . Getting confused by the tables below as table 2 says 15m and table 1 says 6m ? Can anyone help?

 

[Ben-gee]

I think it’s 6m from wc to main vented stack.

ie 6m is the longest you can go ‘upstream’ of a vent.

Once you are going away from the vent I don’t think there’s a limit? As long as you maintain 18mm fall per metre.

I guess if it went really far (not exactly an SI unit I know) it would be a good idea to put in another vent stack.

What’s your situation?

 

[Piperdave22]

@Ben-gee What do you mean by go away from the vent ?
Basically a customer is in a terraced house the only drain is in the back garden of a single story extension with a pitched roof which is where the bathroom is and all wastes go to a gully with a grill apart from the 4 inch which is coming out in the bathroom and going straight into the pan connector
They want a toilet and basin in the middle of the house which would mean connecting into the drain out side with a new connection , running pipe up the outside wall with a vent and going through the wall an roof void until you get to the bedroom but there will be some bends because of roof trusses etc .
This run is longer than 6 metres and I want to make sure it is done right because obviously the drains will have to be signed off as it will change them on the deeds etc and don’t want a call back if they ever try to sell.
The only other option i can see is a saniflo which id rather avoid because of the noise and maintenance but may be the only option if the soil pipe doesn’t conform .
What are your thoughts?

 

[Ben-gee]

I think that will be notifiable so you’ll have to get building control involved anyway.
Chat to your bco and get them to do a site visit if necessary.

 

[SimonG]

As above. I just get building control and ask them what they want. They're the ones signing it off.

 

[centralheatking]

Whilst I always observe building regulations and all authority there
are occasions in old buildings where practical experience can produce a solution. Drainage is one. Almost horizantal soil pipe
4 or 6 inch in straight runs will perform providing
1. Input is from reasonable height
2. Output discharges vertically to reasonable depth.
We have practical experience of this in listed buildings in Bath
centralheatking....often the conservation architect calls the shots
over the building inspector in my experience
centralheatking

 

[CHRISX]

As above really what’s the max length a soil stack can be run horizontally, it will be feeding a toilet and a basin . Getting confused by the tables below as table 2 says 15m and table 1 says 6m ? Can anyone help? View attachment 39978

Hello Piperdave22,

Unless there is a good reason it is always good practice to put a Vent pipe at the end of a long Soil float pipe.

Not doing so in some circumstances would mean that the float would not be approved by the Local Authority Building Control Officer.

After liaising with a Local Authority Building Control Department / Building Control Officer to get approval for what I had planned I have run a Soil float pipe 30 metres along a Building picking up 6 Office Toilets / W.C. & Basins and 2 Kitchen Sink wastes but I installed a 100mm Soil Vent pipe at the end of the run and behind every branch from a W.C. Pan [externally] - and of course there was a Vent on the 150mm Soil stack.

I probably could have only installed a Vent at the end of the run and 2 more equidistant along the float between the end and the Soil stack but for the sake of not much more work and materials I wanted to ensure that in the unlikely event of all of the Toilets being flushed simultaneously none of the W.C.`s / Basin or Kitchen Sink traps would be siphoned.

This was done / approved by the LABC because there was no way to install new Drainage to take 3 additional Soil stacks [which would have been the `normal` way to go] because the land below the new Toilets etc. was owned by another Company and could not be excavated for Drains because of there being a brick paved Car Parking area with Electrical cables / Water Mains and Fibre Optic cables adjacent the wall - nor would the owners have allowed Drains to be put there.

If You want to install a long Soil float either very close to the prescribed length limit or over it I would always advise venting at least the end of it.

But very importantly - as other Members have correctly advised You should always obtain Local Authority Building Control approval for what you plan to do otherwise any `non approved work` would be condemned and Labour and Materials wasted as well as your reputation with the Client damaged.

Chris

 

[Piperdave22]

Sorry for the late replies ! Normally get notifications by email when there is replies but doesn’t seem to have happened this time!
Thats exactly what I did , i spoke to my local building inspector and he said “15metres from a vented soil stack max which your not really going to get to in a standard house anyway and 6m from an unvented soil stack.

 

[CHRISX]

Hello again Piperdave22,

Do You mean that you were told by the Building Control Officer that you could run a Soil branch float up to 15 metres with a vent at the end of the float - and run a Soil branch float without a vent at the end to 6 metres maximum length ?

Any long branch float would have to go into a Soil stack that had a Vent.

A long float should never be going into for example a Stub stack or a Soil stack with an Air Admittance Valve [AAV] unless a vent at the end of the float was approved as becoming the `main vent` and there was no siphoning of a W.C. Pan or any traps.

Chris

 

[centralheatking]

Aav are ok but there is little better than a proper 4inch stink stack
properly positioned and terminated correctly. centralheatking

 

[Piperdave22]

Hello again Piperdave22,

Do You mean that you were told by the Building Control Officer that you could run a Soil branch float up to 15 metres with a vent at the end of the float - and run a Soil branch float without a vent at the end to 6 metres maximum length ?

Any long branch float would have to go into a Soil stack that had a Vent.

A long float should never be going into for example a Stub stack or a Soil stack with an Air Admittance Valve [AAV] unless a vent at the end of the float was approved as becoming the `main vent` and there was no siphoning of a W.C. Pan or any traps.

Chris

Yeah so basically it would connect into the drain outside , run up the wall tee in to a max of 15m horizontal length ,then carry on to vent above roof .

But if it was just going straight from drain underground up to toilet with no vent for example the max is 6m

This is what I was told by the building inspector

 

[CHRISX]

Yeah so basically it would connect into the drain outside , run up the wall tee in to a max of 15m horizontal length ,then carry on to vent above roof .

But if it was just going straight from drain underground up to toilet with no vent for example the max is 6m

This is what I was told by the building inspector

Hello again Piperdave,

Obviously You should believe what you state that the Building Control Officer / Building Inspector told you as he or a colleague will be passing the Soil stack and Soil stack test - but there is no way that I would install anything like a 15 metre Soil Float / Soil stack branch pipe into a Soil stack without there being a Vent pipe [100mm] at the end of the Float.

I don`t want to annoy You by suggesting that you might have misunderstood what he was describing but nor would I want you to install a very long Soil Float without a Vent pipe at the end of the Float and have the Building Control Officer tell you that he meant there should be a Vent at the end of a long / 15 metre maximum Soil Float / Soil Branch pipe.

If what I describe is what he meant and you had to alter the end of the Float some Building Control Officers can be pedantic enough to require that the Vent is actually at the end of the Soil float - they may not allow just a Branch to be cut into the Float immediately downstream of the bend to the W.C. Pan.

Good Luck with whatever You decide to do - I hope that the Soil stack and Float passes the Building Control Inspection and Testing.

Chris