Waste Pipe Vent or No?

[James Davis]

Hi all!

I've attached a plan below. Side extension is being built, it includes a WC. Toilet waste pipe will go straight out the wall and then down into the ground on the outside.

I want to avoid an unsightly stack on what will be the front of the house extension. So preference is a low sub stack at ground level, quite short. However, I understand a vent might be needed on it, a special type, meaning it will end up being 1m high.

If you look at where I've marked 'A' in a circle, that is an existing soil pipe with a passive vent on the top, above eaves level. It is connected to two toilets which are located on the other side of the wall from it.

Question: can the new toilet just be served by the existing vent? It would be over 6m from the new toilet but not much more. Perhaps 6.5m. I cannot find information on this specific question as people seem to be talking about toilets sharing a line..?

Thanks

 

[noseall]

Hi all!

I've attached a plan below. Side extension is being built, it includes a WC. Toilet waste pipe will go straight out the wall and then down into the ground on the outside.

I want to avoid an unsightly stack on what will be the front of the house extension. So preference is a low sub stack at ground level, quite short. However, I understand a vent might be needed on it, a special type, meaning it will end up being 1m high.

If you look at where I've marked 'A' in a circle, that is an existing soil pipe with a passive vent on the top, above eaves level. It is connected to two toilets which are located on the other side of the wall from it.

Question: can the new toilet just be served by the existing vent? It would be over 6m from the new toilet but not much more. Perhaps 6.5m. I cannot find information on this specific question as people seem to be talking about toilets sharing a line..?

Thanks

Put the hand basin right in the corner, shift the loo over a wee bit and have the stub stack in the internal corner of the WC. Simples.

 

[James Davis]

But my main question is: does the new toilet waste pipe need to be vented or is the existing soil pipe sufficient?

Incidentally, I don't really want the stack on the inside taking up room and I don't want any right angles in the waste pipe. I want a straight connection out the back for a more efficient flush and removal of ****. I don't have a problem with the stack being on the outside providing it is small and low down (not vented). Also more accessible for hosing down if its be.

 

[noseall]

But my main question is: does the new toilet waste pipe need to be vented or is the existing soil pipe sufficient?

As long as the head of the drain is vented, then there is adequate ventilation to the system.

Incidentally, I don't really want the stack on the inside taking up room

You don't want the stub stack inside and you don't want it outside.....

and I don't want any right angles in the waste pipe.

Okay....

I want a straight connection out the back for a more efficient flush and removal of ****. I don't have a problem with the stack being on the outside providing it is small and low down (not vented). Also more accessible for hosing down if its be.

The stub stack will finish as high as the basin waste.

 

[noseall]

I want a straight connection out the back for a more efficient flush and removal of ****.

Fit access fittings on vulnerable junctions.

 

[James Davis]

So the one vented soil pipe already there is sufficient?

I don't mind the stack being outside and even prefer it, but not if it is too tall. My builder suggested 1m high but that was because he assumed it needs a vent on it, a special one that let's air in but not out.

The stack can be quite low then I assume? Not much taller than the toilet waste pipe and the sink waste pipe could slope down inside and then go outside quite low?

Incidentally, can the sink waste pipe go into the toilet waste pipe inside?

 

[James Davis]

Put the hand basin right in the corner, shift the loo over a wee bit and have the stub stack in the internal corner of the WC. Simples.

I have an existing toilet in an ensuite where a so called question mark connector had to be used to achieve a right angle at the back of the toilet, and then concertina ****e was used as part of the waste connection because some flexibility was needed in a tight spot. It doesn't flush as well as I'd like so I'm set on the idea now, in this new loo, of having a simple waste pipe that goes straight from the back of the toilet, through the wall and then down the drain. I won't right angles happening on the horizontal plane. An internal stack would cause this.

 

[Hugh Jaleak]

Existing Vent should suffice, as long as there's one open vent on the system, I don't see there being an issue.

New WC, it's on the ground floor, so can be directly connected to the drain provided the drain is less than 1.3m deep at that point. It can under the floor and out through the wall underground, no unsightly pipework inside or out then. Basin waste can be coupled on via the Pan Connector internally.

 

[James Davis]

Thanks Hugh.

This 1.3m depth... you can see the open ended pipe the toilet will connect to, where is the lowest point counted as - the horizontal run of orange pipe or the chamber it is going to? Why is 1.3m important, what would 1.5m cause?

Also, sorry to throw in another question, am I right in saying the foul drain pipes shown need to be a minimum of 1:80 gradient?

 

[noseall]

Also, sorry to throw in another question, am I right in saying the foul drain pipes shown need to be a minimum of 1:80 gradient?

1:40 (25mm every metre) is preferable. However, they will function (plastic) with much less fall, yes.

 

[Ivor Windybottom]

1:80 if there's a toilet, 1:40 if not.

This is the correct way around, I had a lifelong drains expert giving me a quote telling me the opposite with great authority.

The toilet flush will keep the pipe clear, so it's allowed to be less steep.

 

[Ivor Windybottom]

Drainage and waste disposal: Approved Document H

Building regulation in England for foul water drainage and disposal.

www.gov.uk

 

[Ivor Windybottom]

 

[Ivor Windybottom]

Whatever gradient, it's advisable to keep it as constant as possible.

 

[James Davis]

So we are achieving 1/60 on the foul drain line. Just shy of 17mm fall per metre when measured. By the looks of it, you can be allowed to have less so that is reassuring. Flow works based on test. Although I've noticed some residual water does sit at the bottom of the plastic inspection chambers in the main through channel - is this normal?

What is annoying about these plastic inspection chambers is that whilst the main inlet is low, the rest of the branches are about 2" higher. We are having to go into one of these higher inlets with the main foul line at the final chamber and it steals a good bit of gradient. We have no choice because we are connecting in to an existing clay pipe system. Having said that, we don't want th gradient to be too steep since that can be as bad as not enough (water flows faster than logs etc).

What I don't get is why (third column of table), higher litre capacity is needed when peak flow is <1?