Anyone understand Approved Document H - length of WC branch?

[Ric2013]

I'm just trying to get my head around this one. I need to understand this stuff for my NVQ.


Table 2, page 9, 'Common branch discharge pipes (unventilated)' tells us:

The WC outlet can have a maximum 15m unventilated branch and that a maximum of one WC can connect if the outlet is less than 80mm, or up to eight WCs if the outlet is greater than 80mm.

Diagram 3 (below table 2) shows:

The WC branch is a maximum of 6m length for single WC.


This seems to me to contradict. I can understand that one WC can have a 6m branch, and more than one WC can have a 15m branch.

What I don't get is how table 2 says that we are allowed no more than 1 small-outlet WC on a 75mm branch, but that the length of that branch can be 15m when the next diagram shows that the limit is 6m for a single WC. If we are only allowed one WC on a 75mm branch then surely table 2 should state that the maximum length for this is 6m instead of the 15m figure it gives?

I'm wondering what they mean by 'common branch' and whether my failure to grasp this is the reason I think there is a contradiction.

Any thoughts appreciated.

Thanks,

Ric

 

[JCSPLUMBING]

The 6m rule on 110mm soil pipe is for unventilated runs to stop induced siphonage

 

[Ric2013]

So is the 15m on table 2 (which IS for unventilated) a typographical error, do you think?

 

[chris watkins]

It is not clear that is for sure but my take on it is as follows -
Diagram 3 "Branch connections" limit of 6 Metres is for a single appliance (in this case a WC) connected to a discharge stack by a single pipe (unventilated) and as far as any exam questions are concerned this is the one they will ask about, so stick with this.

Table 2 Common branch discharge pipes (unventilated) I believe relates, as the name suggests, to a common branch where more than one appliance connects into that branch pipe (or as I call it a float) as it runs to the stack.

Need to have a look at BS EN 12056 Gravity drainage systems inside buildings. which can also be used.

All modern pans are >80mm, rules on the <80 are so that self cleaning velocity is maintained with out risk of blockage or surcharging to branch.

 

[Ric2013]

Hi Chris,

Oh, I'm sure they want the 6m answer - funny how everything gets simplified for the NVQ, but then we all know what NVQ stands for . And I'm sure at college I'll probably get a confused teacher too. Actually, I'm lucky in that at least my training centre has staff with a reasonable experience of domestic plumbing (although I reckon no one there has run a 15m branch because that's a mansion, or prison).

Struggling slightly with getting British Standards at present. Used to log in using Essex Libraries website, but have since moved to Powys and not sure whether I can get in the same way.

I think then that we understand the 'common' bit the same way. Obviously even a handwash basin would help flush the branch out after use (if people wash their hands...)