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Maximum Height for Soil Branch to WC

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Hi All,

Need some advice with regards to what has been installed in our new build. The main foul run enters the house through the floor in the downstairs WC. A branch connector comes off this to run to the WC in this bathroom with the run continuing up through the house as normal to a slate vent.

The problem is the height of the connection in the downstairs bathroom to the WC. The floor has been screeded and will be tiled on top. At the minute the branch connector is, in my opinion, too high off the floor. The distance from the floor to the midpoint of the soil run to the WC where it leaves the branch is 7.5". I have a temporary WC fitted in this bathroom and with it sitting on a piece of 18mm flooring the soil run to the branch is level! Our tiles with adhesive are likely to be around 15mm max I would have thought meaning the soil run will be flowing back to the toilet!! The plumber who installed it is insisting 7.5" is the standard height to set a run like this off the floor. Can anyone point me to any guidance on this?

Lowering the branch is a real problem as the collar through the screed floor is above the floor level and the branch connector won't go any further down.

Any suggestions apart from digging up the floor and lowering the collar?

Thanks in advance.
 
I think that you will have a problem in complying with part H of the building regs, for a start, "minimum distance from the transition of the soil stack to a drain to a branch to be 450 mm", and might have compression problems if the branch to the soil stack is lower than this

To be sure that there will not be a back fall on the w/c branch to the soil stack is to measure the outgo of the actual w/c pan that you will be useing

I think that the plumber is about half an inch too high with his measurements, standard centre line of the w/c outgo in France is 180 mm = 7 inches
 
Plouasne said:
I think that you will have a problem in complying with part H of the building regs, for a start, "minimum distance from the transition of the soil stack to a drain to a branch to be 450 mm", and might have compression problems if the branch to the soil stack is lower than this

To be sure that there will not be a back fall on the w/c branch to the soil stack is to measure the outgo of the actual w/c pan that you will be useing

I think that the plumber is about half an inch too high with his measurements, standard centre line of the w/c outgo in France is 180 mm = 7 inches
Click to expand...

Thanks for the reply.
Not sure about exactly what you mean in your first statement. The Building Inspector has already seen the initial foul runs before screeding and all has been passed. I've attached a photo of the setup in the downstairs bathroom. The main soil run enters in the far corner under the current grey branch which leads to the problem WC.

Hope this makes it more clear. As stated at present with the WC on 18mm of wood, the run is level to the branch.

Hope that helps and thanks for the reply.
 

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Plouasne said:
I think that you will have a problem in complying with part H of the building regs, for a start, "minimum distance from the transition of the soil stack to a drain to a branch to be 450 mm", and might have compression problems if the branch to the soil stack is lower than this

To be sure that there will not be a back fall on the w/c branch to the soil stack is to measure the outgo of the actual w/c pan that you will be useing

I think that the plumber is about half an inch too high with his measurements, standard centre line of the w/c outgo in France is 180 mm = 7 inches
Click to expand...
But the soil pipe obviously goes under the ground after the branch otherwise all downstairs toilets would have to be 450mm off the floor!
7 1/2" inches is standard in U.K. but you need a fall to the branch.
A lot of U.K. new builds use wall hung pans now which have higher outlets at around 9 1/2"
 
Ockyvines said:
But the soil pipe obviously goes under the ground after the branch otherwise all downstairs toilets would have to be 450mm off the floor!
7 1/2" inches is standard in U.K. but you need a fall to the branch.
A lot of U.K. new builds use wall hung pans now which have higher outlets at around 9 1/2"
Click to expand...

Thanks for that. Unfortunately this WC won't be wall hung. It will be standard floor mounted. It only needs a slight fall due to the distance but unless I use particularly thick floor tiles, it will not have any fall and may even have a fall towards the WC.
 
Is it an optical illusion, it looks like there is a fall.
You only need a surprisingly small fall for it to work effectively
 
Ockyvines said:
Is it an optical illusion, it looks like there is a fall.
You only need a surprisingly small fall for it to work effectively
Click to expand...

It looks like that in the photo but putting a spirit level on it shows it pretty much level at the minute. With tiles and adhesive any less than 18mm, there definitely won't be a fall.
 
I have just had another look at the photo.
The branch fitted is a "double bossed" type.
If changed for "single boss" you would probably gain 1 1/2" or so
 
Ockyvines said:
I have just had another look at the photo.
The branch fitted is a "double bossed" type.
If changed for "single boss" you would probably gain 1 1/2" or so
Click to expand...

That would do it nicely :). Only need a single boss one so if that will lower it by an inch or more, that's perfect.

Thanks.
 
I refer to the current building regulations part H, diagram 2 to be precise, this can be downloaded from the government web site (type in building regs part H, in a search engine and then down load the document)

But the particular portion of the regs I am referring to, state that there shall be no branch connection lower then 450 mm measured from the invert of the drain to the centre line of the branch, in your case it would mean that the bottom of the drain should be at least 280 mm below the top of the slab level

If the bottom of the drain is lower than the minimum distance, IE is more than 280 mm below the slab level, the plumber can cut off bottom blind boss connections and half an inch off the branch to lower the branch, so no problem with a possible back fall
 
Plouasne said:
I refer to the current building regulations part H, diagram 2 to be precise, this can be downloaded from the government web site (type in building regs part H, in a search engine and then down load the document)

But the particular portion of the regs I am referring to, state that there shall be no branch connection lower then 450 mm measured from the invert of the drain to the centre line of the branch, in your case it would mean that the bottom of the drain should be at least 280 mm below the top of the slab level

If the bottom of the drain is lower than the minimum distance, IE is more than 280 mm below the slab level, the plumber can cut off bottom blind boss connections and half an inch off the branch to lower the branch, so no problem with a possible back fall
Click to expand...

The bottom of the drain is MUCH lower than the minimum. There is 50mm of liquid screed, 200mm of insulation followed by the beam & block floor and then a substantial air gap plus the drop underground to the main run!
Think I'll just buy another single boss and drop it that way.
 
Ockyvines said:
But the soil pipe obviously goes under the ground after the branch otherwise all downstairs toilets would have to be 450mm off the floor!
7 1/2" inches is standard in U.K. but you need a fall to the branch.
A lot of U.K. new builds use wall hung pans now which have higher outlets at around 9 1/2"
Click to expand...

Ocky,

Never heard of compression at the foot of a soil stack ??, that's why the regulation was brought in

If the branch connection was within proscribed distance, somebody contemplating on the down stairs w/c, could have something to contemplate about if the upper floor w/c was flushed, like the water seal in the downstairs w/c trap, giving their backside an unwelcome wash
 
Plouasne said:
Ocky,

Never heard of compression at the foot of a soil stack ??, that's why the regulation was brought in

If the branch connection was within proscribed distance, somebody contemplating on the down stairs w/c, could have something to contemplate about if the upper floor w/c was flushed, like the water seal in the downstairs w/c trap, giving their backside an unwelcome wash
Click to expand...
Yes I know all about that but this is a 21st century new build so is going to have the necessary height
 
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