A long run on toilet waste pipe, under loft-room floor!

[JAD]

Can somebody please advise me?
I am planning on putting a shower, basin and toilet en-suite to a loft conversion bedroom. The intended location will involve running the waste pipes under the floorboards 4.5 metres across the room before dropping down to the existing soil stack. I am not too concerned about the shower and basin waste but is running the soil pipe from the toilet under the floorboards a bad idea? The floor joists seem to be about 180mm (7") deep and therefore I should just be able to get the 18mm to 1 metre decline required by building regs(?). I have considered a Saniflow but want to avoid this if at all possible!

Any advice would be gratefully received.

JAD

 

[mercurygas]

According to our local Building Inspector, If the existing stack that serves lower floors you should not join into it but drop a new waste down to the nearest manhole. If you were to have a block between the manhole and lower floor when you flush the upstairs one it will surface in the lower pan OOOOhhhh Nasty

 

[Softus]

If you were to have a block between the manhole and lower floor when you flush the upstairs one it will surface in the lower pan OOOOhhhh Nasty

Well yes, but the same flooding would occur if you flushed the lower WC, even if there was no upstairs WC

You've worked out the fall correctly, and I've seen longer runs on branches, so I don't see a problem with what you're planning to do - obviously it's not ideal, but you've already said that you're implementing a comprimise.

 

[mercurygas]

Well if this is being supervised by Building Control they will ask for a drains test which involves plugging at the manhole and flushing the toilet upstairs, heh presto water all over the downstairs loo floor. The upstairs one should hold the 6 Litres for a period, this will not happen in this case.

 

[Softus]

mercurygas, your reasoning started out unclear, and is getting muddier.

You first stated that your LABC advised (i.e "should" not, not must not) not to connect onto the existing stack, and that the reason given was the potential flooding out of the lower WC pan if an underground section blocked.

I then pointed out that you cannot prevent flooding out of the lower pan by having separate stacks.

You then raised a new objection, which is that a soundness test cannot be conducted, because water would emerge from the lower pan. This is also wrong, because heh presto (sic.) this would happen even with seperate stacks, for which reason the lower pan would be removed for the purpose of such a test.

So, what's your real reason for objecting to the OP's idea?

 

[mercurygas]

Not true, seperate stacks will not flood downstairs, how can it? Just ring Building control

 

[Softus]

Not true, seperate stacks will not flood downstairs, how can it?

We must have crossed wires, because I think it's obvious and you think it's impossible.

If there's an underground blockage after the junction of the two stacks, and the manhole preceding that blockage fills up, then water (and other stuff!) will back up to the lowest WC and it will then overflow. This will happen regardless of whether water is flushed from that WC or a higher one, or one on a different stack.

Just ring Building control

Why? Will they teach me something about plumbing and drainage that I don't already know? I get on very well with my LABC, but he knows that I know more than he does.

 

[Agile]

"""Why? Will they teach me something about plumbing and drainage that I don't already know? I get on very well with my LABC, but he knows that I know more than he does."""

Well lets face it, Softus knows more about plumbing and gas boilers that all the rest of us combined!

 

[Softus]

Well lets face it, Softus knows more about plumbing and gas boilers that all the rest of us combined!

I don't know why you would write that, other than to be ineffectually sarcastic.

I have never claimed to know more than anyone else on the forum on the subjects of plumbing and gas. I certainly know less than you do Agile, and the same goes for many others. However, it does appear that many RGIs on this site either don't read, or don't understand, the legislation that governs their trade. The situation becomes apparent in most discussions about what a DIYer can and can't tackle.

 

[kevplumb]

If there's an underground blockage after the junction of the two stacks, and the manhole preceding that blockage fills up, then water (and other stuff!) will back up to the lowest WC and it will then overflow. This will happen regardless of whether water is flushed from that WC or a higher one, or one on a different stack.

obvious to me softus FWIW

and stop biting

 

[mercurygas]

Ok, so if there is a block on a single stack serving two different levels BEFORE the manhole junction it will flood the lower of them, if the same block occurs the other stack is unnaffected. That is all i was trying to say.

 

[Nige F]

I think you should have a 2 stack fully vented system using cast iron soil and lead vent pipes.....so the house looks like a Victorian Institution, like where I am now Fall.........1:40 is plenty for plastic 100mm soil..............10mm in 400.........less is not a prob. because the bore is smooth ........You may have to employ a plumber to put a rational argument to B.C...for one stack....the odds may be stacked against you

 

[JAD]

Gentlemen gentlemen!
Thank you for your input. I now appreciate its a close-call and the cautious approach may be the most sensible? That is, going for a Saniflow! However, if I fit a macerator are you all saying that this too could cause problems if fed into the same soil stack as the loo on the first floor?

 

[scatmanjohn]

JAD wrote:

That is, going for a Saniflow! However, if I fit a macerator are you all saying that this too could cause problems if fed into the same soil stack as the loo on the first floor?

Don't do it please.

Them things are the spawn of the devil.

Juk!!!!!

 

[Softus]

I think you might be trying to apologise, but in case you're not, may I remind you that you said this:

Not true, seperate stacks will not flood downstairs, how can it? Just ring Building control

and then you said this:

Ok, so if there is a block on a single stack serving two different levels BEFORE the manhole junction it will flood the lower of them, if the same block occurs the other stack is unnaffected. That is all i was trying to say.

When I had long since said this:

Well yes, but the same flooding would occur if you flushed the lower WC, even if there was no upstairs WC.

But, on a lighter note, Nige said this:

...the odds may be stacked against you

Toilet puns are always the best

-----------------------------------------

...if I fit a macerator are you all saying that this too could cause problems if fed into the same soil stack as the loo on the first floor?

You betcha! You'd still be emptying the contents of the cistern (and your bottom) down the stack - same quantity, same problem, only it would be a problem chopped up into little bits

However, my point all along is that you can't cause a problem by emptying into the same stack, you would merely be able to flood the downstairs WC from two places - its own cistern and the one upstairs.

There are other reasons for not choosing a macerator. Search for the words "macerator" and, as scatmanjohn helpfully pointed out, "devil", and you'll have some images in your head that you'd rather not have had.