New WC >6m from stack?

[gasket]

Hi. Hoping for some advice.

Our house had a downstairs WC and shower fitted by the previous owner. We pulled it out and are about to replace it with a WC and basin.

The soil pipe is in situ (which will take both the WC and sink waste) but I’m concerned about the vent stack, which is around 7.5m/8m from the WC.

My understanding is that 6m is the maximum and that a new stack is needed. But I don’t know if that means a complete second vent pipe running all the way up through the roof or if there is some sort of low level vent that can be used within the new downstairs bathroom itself. Through the roof is doable, but I don’t want to go to all that expense if there is a simple solution that puts a vent adjacent to the loo itself.

Can anyone advise?

Thank you.

 

[Hugh Jaleak]

Regs allow up to 15m on an Unventilated Branch, although I'd probably stick an AAV on the end for belt and braces.

 

[Madrab]

Regs allow up to 15m on an Unventilated Branch, although I'd probably stick an AAV on the end for belt and braces.

Always found that part of the regs contradictory, why that section in the regs - in table 2 - gives max discharge branch length as 15m but in the branch connection diagram it states 6m??

 

[denso13]

understanding is that 6m is the maximum

Yes, for a single WC only, but longer becomes compliant with an internal AAV fitted next to the loo.

 

[Hugh Jaleak]

Always found that part of the regs contradictory, why that section in the regs - in table 2 - gives max discharge branch length as 15m but in the branch connection diagram it states 6m??

View attachment 409551

Yet if you're doing a direct connection to the drain, the underground run can go the length of the property if needs be, often in excess of 15m... I really fail to see the issue provided the run is set to a suitable fall!

 

[Madrab]

Yet if you're doing a direct connection to the drain, the underground run can go the length of the property if needs be, often in excess of 15m... I really fail to see the issue provided the run is set to a suitable fall!

Yeah - and when it comes to real world practicalities, as long as the run is self cleaning and doesn't create any issues. It just seems pointless to have 2 contradictory standards side by side though the thinking is there must be a reason otherwise it wouldn't be there - or so you would think.

Wouldn't be the first time regs contradict themselves

 

[denso13]

It just seems pointless to have 2 contradictory standards side by side though the thinking is there must be a reason otherwise it wouldn't be there - or so you would think.

One is for single appliances connected, the other is for discharge branches with multiple appliances connected.

 

[Hugh Jaleak]

One is for single appliances connected, the other is for discharge branches with multiple appliances connected.

Discrepancy is though, wording in "Table 2, "Common Branch discharge pipes (Unventilated)" is "Max no. to be connected" and underneath in the table, "WC outlet > 80mm 8". The single WC mention comes below in Diagram 3.

There is no clarification where that number can be increased or at what length of branch. I honestly don't see the issue, provided the run is straight and on a suitable fall.

 

[Madrab]

I honestly don't see the issue

Absolutely and in practice there certainly shouldn't be a problem.

It does seem though that the OP did check the regs, hence his 6m max length question, which is relative to his situation with the single WC into a stack and when it's looked at then it really shouldn't have a problem. The trouble is the regs aren't clear and it seems they could be made clear quite easily.

Anyways .... @gasket , the consensus is - knock yourself out but you may want to vent the run just in case, if there's a basin to be connected though ideally the vent should be above the spill over level of the basin and/or could use an anti vac trap. The vent could be say on a piece of 50mm waste extended up from the toilet soil pipe end or slotted into a pan connector with boss, it wouldn't really need to be 110mm or up through the roof really I wouldn't think

 

[denso13]

I honestly don't see the issue, provided the run is straight and on a suitable fall

Neither do I.

But in the OP's case, for a single WC, the maximum in the guidance is 6m without additional ventilation. A low level AAV is fine.