Siting of main stopcock

[JohnW2]

As I recently mentioned in another thread, I find myself with a house that has a (very limited) pre-WWII plumbing installation, which clearly will; have to soon be replaced 'from scratch'. I'm therefore starting to think about some of the concepts of design of that new plumbing system.

My first question is pretty simple, and must be one which fairly often arises. The house is quite narrow and 'long', and below is a diagram of how the supply gets into the house (in fact, it's more-or-less a diagram of the entire current plumbing system!)

Water enters the house under the front door, and there is a stopcock at that entry point. However, it's about 500mm below the floorboards, and obviously will eventually be covered by floorboards and floor coverings ,hence useless as a functional stopcock (although there is one in the pavement, adjacent to a meter) which I am currently using).

The natural routing of the new pipework would be essentially the same as at present, with an (inaccessible) under-floor run of about 12m of pipe to the kitchen sink, which is also roughly the most logical place from which pipes would rise to feed the bathroom(s) immediately above. The first 'accessible' place for a main stopcock would therefore be 'under the kitchen sink'.

Would that arrangement be reasonable/'acceptable' (I suspect it must be pretty common!)? It theoretically leaves that ~12mof unfloor pipe upstream of the 'main stopcock', although I suppose that the chances of any problems with that are very small. I suppose one could bring the pipework up to above floor level near the from door, through a stopcock and then back down to under the floor - but that would hardly be 'neat'. What is usually done in this situation?

On a totally different issue (because it's currently in my mind!) it looks as if at least some of the soil stack is going to have to be replaced. Although it's not something I can recall having seen done, would it be sensible to ask for access for rodding to be incorporated above the highest feed into the stack?

Kind Regards, John

 

[denso13]

Would that arrangement be reasonable/'acceptable'

Yes, insulate below the floor then stopcock below the sink.

lthough it's not something I can recall having seen done, would it be sensible to ask for access for rodding to be incorporated above the highest feed into the stack?

Not normal, but won't do any harm.

 

[JohnW2]

Yes, insulate below the floor then stopcock below the sink.

Thanks for your very rapid response.

Does insulation actually achieve anything much, given that all it can do is reduce the rate of heat loss from the pipe? If the house were unoccupied (as it has been for 20+ years!) and if the below-floor temperature fell to sub-zero (probably unlikely, even if unoccupied), then the temp of the contents of the pipe would fall to sub-zero eventually (and hence freeze), even with insulation - merely more slowly than would be the case without insulation.

Not normal, but won't do any harm.

As you say, it obviously wouldn't do any harm, but is there any point, if it's not normally done? Is the implication that a blockage in a vertical run of soil pipe is very rare?

In passing, I've often wondered whether a 'vent' pipe of a soil stack (i.e. above the highest feed into it) really needs to be anything like as big (e.g. 110 mm) as the soil pipe, since I would have thought that in terms of both 'air admittance' and 'discharge of gases', a much smaller pipe would probably be adequate?

Kind Regards, John

 

[denso13]

then the temp of the contents of the pipe would fall to sub-zero eventually (and hence freeze), even with insulation - merely more slowly than would be the case without insulation.

Yes, if left long enough. I would be treating it as a pipe in an unheated void and still be insulating it. If it is going to left regularly for long periods over winter I would be looking at a way of installing it so it could all (or as much as possible) be drained down.

In passing, I've often wondered whether a 'vent' pipe of a soil stack (i.e. above the highest feed into it) really needs to be anything like as big (e.g. 110 mm) as the soil pipe, since I would have thought that in terms of both 'air admittance' and 'discharge of gases', a much smaller pipe would probably be adequate?

It could be min. 75mm, but I've never bothered to reduce it.

 

[JohnW2]

Yes, if left long enough. I would be treating it as a pipe in an unheated void and still be insulating it. If it is going to left regularly for long periods over winter I would be looking at a way of installing it so it could all (or as much as possible) be drained down.

That's what I would like to be able to do but, short of having some sort of access hatch through floorboards and floor covering, it would presumably only be possible if the entire pipe run were above floor level, which is effectively impossible, since (quite apart from aesthetics) the pipe would then cross doorways and goodness knows what else!

It could be min. 75mm, but I've never bothered to reduce it.

I'm a little surprised that it needs to be even that big, but had just wondered why people don't seem to reduce it at all.

Kind Regards, John

 

[denso13]

That's what I would like to be able to do but, short of having some sort of access hatch through floorboards and floor covering, it would presumably only be possible if the entire pipe run were above floor level, which is effectively impossible, since (quite apart from aesthetics) the pipe would then cross doorways and goodness knows what else!

Perhaps some trace heating for the coldest periods?

I'm a little surprised that it needs to be even that big

Approved doc H (of which we both know the legal status...)

 

[JohnW2]

Perhaps some trace heating for the coldest periods?

That's obviously a possibility - although, in practice, if the place is unoccupied, the entire electrical system will usually be de-energised!

Yes, if left long enough. I would be treating it as a pipe in an unheated void and still be insulating it.

I forgot to ask - to what extent would youinsultate it? Just with standard 'slip over' insulation which provides something like one inch of foam around the pipe?

Approved doc H (of which we both know the legal status...)

Fair enough, but I still have to wonder 'why?' it necessarily has to be as large as 75mm. In any event, that 'dispensation' would not apply to the house in question, which has three stories - so, at least as far as the Approved Doc is concerned, I'm stuck with 110 mm.!

Kind Regards, John

 

[denso13]

Just with standard 'slip over' insulation which provides something like one inch of foam around the pipe?

Yes, (another) bylaw, 49, says something like 20mm thick.

Fair enough, but I still have to wonder 'why?'

Probably because there could be a large number of appliances connected and hopefully someone, somewhere, has calculated air intake/ventilation requirements on a worst case scenario.

 

[JohnW2]

Yes, (another) bylaw, 49, says something like 20mm thick.

I seem to recall that Bylaw 49 says 25mm for 15mm pipe and 19mm for 22mm pipe - but my understanding (maybe wrong?) is that relates to the provisions of "overnight frost protection" in occupied premises - hence (if true) probably pitifully inadequate for the longer-term sub-zero ambient temperatures I'm considering. ... and, in any event, those figures presumably must rely on assumptions about the type of insulation?

Probably because there could be a large number of appliances connected and hopefully someone, somewhere, has calculated air intake/ventilation requirements on a worst case scenario.

One would imagine so, but such 'worst case scenario' approaches can get pretty silly. Probably more sensible to adopt the approach of electricity regulations and allow the concept of 'diversity' to be taken into account - since if one didn't (i.e. considered all final circuits being maximally loaded simultaneously) one would end up concluding that all CUs being grossly overloaded, with cutout fuses at risk of blowing all over the place

In any event, wouldn't the "75mm minimum" requirement of App Doc H still apply even if the stack only served one WC, and no other 'appliances'?

Kind Regards, John

 

[denso13]

hence (if true) probably pitifully inadequate for the longer-term sub-zero ambient temperatures I'm considering

Yes, you're on a hiding to nothing with insulation if you are going to leave it live in an unoccupied property for any length of time. If the power is also going to off you'll need to find a way of draining all the pipework.

In any event, wouldn't the "75mm minimum" requirement of App Doc H still apply even if the stack only served one WC, and no other 'appliances'?

Yes. But as you know, it's only guidance. If you only have one WC connected it should be fairly easy to justify a smaller vent.

Probably more sensible to adopt the approach of electricity regulations and allow the concept of 'diversity' to be taken into account

Is there a minimum cable size for a ring final circuit? Could I wire the sockets in 1mm² (or less) if I was only ever going to use 1 table lamp? Not an exact comparison, I know.

 

[JohnW2]

Yes, you're on a hiding to nothing with insulation if you are going to leave it live in an unoccupied property for any length of time. If the power is also going to off you'll need to find a way of draining all the pipework.

Quite- but as I said, the only 'normal' way of draining pipework which is 500mm below the floor would be to have access therough the floorboards and floor coverings and, as I said, it would not be practical to take the pipe all the way through the house above floor level.
[I say "only 'normal way of draining", since I suppose one might possibly envisage a method of 'blowing out' most of the water whilst it remained below floor! ]

Yes. But as you know, it's only guidance. If you only have one WC connected it should be fairly easy to justify a smaller vent.

True, but I would have thought that a pretty high proportion of stacks would have sufficiently few things connected to it for even the 'worst case scenario' to not require a 75mm vent. However, I guess I must be wrong!

Is there a minimum cable size for a ring final circuit?

Yes,. if you mean a ring final as defined in BS7671, for reasons that most people (including myself) don't understand, there is a minimum of 2.5 mm² T+E (or 1.5 mm² MICC), even though 1.5mm² T+E could have the required 20A current-carrying capacity.

Could I wire the sockets in 1mm² (or less) if I was only ever going to use 1 table lamp? Not an exact comparison, I know.

As above, the answer in terms of BS7671 is explicitly no. However, an electrical sockets circuit with multiple sockets is very different from a soil stack - since the former is designed so that, as it stands, any, and any number of, loads could be plugged into the sockets of the installation, whereas additional appliances could not be connected to a soil stack without 'modifying' the installation.

However, perhaps a closer analogy. If you had a radial sockets circuit protected by a 16A MCB, then you could use 1mm T+E (if installed by Method C). You could not use "less than 1mm²",since that is not allowed (by BS7671) for any circuit (and, until the latest amendment, 1.5mm² was the minimum allowed for a 'power' (sockets) circuit).

Kind Regards, John

 

[cdbe]

I've got 2 WC's on one internal stack (GF and FF), the stack is (successfully) vented by 2x 40mm waste pipes.

It will make you cringe but it's been fine for years.

 

[JohnW2]

I've got 2 WC's on one internal stack (GF and FF), the stack is (successfully) vented by 2x 40mm waste pipes.

As you might expect from what I've written, that does not surprise me at all

It will make you cringe but it's been fine for years.

As above, certainly no cringing from me. It would not surprise me if 32mm waste pipe(s) (or even smaller) would actually have proved adequate. However, I can understand many people feeling that they should follow 'guidance'.

Kind Regards, John

 

[cdbe]

I based my assumption on the fact that a durgo valve ain't letting much air in so as you say, even mine is probably overkill.

 

[JohnW2]

I based my assumption on the fact that a durgo valve ain't letting much air in so as you say, even mine is probably overkill.

Indeed -and I think one thing that perhaps goes overlooked is that, for a given pressure difference/gradient, the size o pipe required to get a certain flow rate of gases is dramatically smaller than that required to get the same flow rate of a liquid such as water.

Whilst accepting that there is always the possibility that I'm wrong, I would therefore have thought that to use 110 mm pipe for, say, just a few feet of 'vent' pipe must be 'dramatically OTT' in relation to what would actually be adequate for the purpose!

Kind Regards, John