Bends and joins in cloakroom drainage

[philrosenberg]

Hi all
I'm looking for some advice when replumbing my (ground floor) cloakroom. The room is very limited for space and was part of a larger extension. In the end the builder left the cloakroom unfinished, for various reasons. I am now ripping the existing T+G floor up to put down a plywood base for tiles and am sorting out the drainage.

I have included a sketch of the current layout (which could change if needed) in black. The soil pipe currently enters the cloak room below floor level through a double skinned brick wall (that used to be the exterior wall before the extension). The other side of that wall is our lounge which has a concrete floor. The builders put in a stub stack with an osmavent underneath the basin. The WC has a hidden cistern inside the cavity, which will have a coloured glass panel to hide it (as well as providing a sanitary "splash back" for the WC). Currently everything is connected into the stub stack above floor level to maintain minimum distance above the invert.

The particularly bad problem with this is that the connection on the stub stack for the washing machine sticks out further than the sink so I can't even box it in. Also the connection for the toilet does a U turn going into the cavity wall then out making it almost impossible to put any sort of façade on that wall.

What I would like to do is move the stub stack into the cavity to hide it and branch the soil pipe below the floor to give me a second stub stack next to the washing machine which I can also hide. I've shown this on the sketch in red. This would hide all my drainage pipework. I've show that on the sketch in red.

However, to me there are two obvious potential pitfalls. The first is that the stack behind the toilet would need nearly a 180 degree bend. Would this be okay if I used large enough radius bends? The second is that I would need to branch the soil pipework below the floor. Would this be okay?

Of course both stub stacks would be accessible so could be used for rodding, but it's obviously better to design things to avoid blockages than simple have the ability to unblock them.

My other option would be to swap the washing machine and WC locations, but I'm not sure how much that helps me.

All advice very gratefully received.

Phil

Untitled

• philrosenberg
• 31 Mar 2015
• 1

 

[philrosenberg]

Got to go buy the parts today, but advice still welcome.

I just checked the building regs, part H

2.20 Pipes should also be laid in straight lines where practicable but may be laid in slight curves if these can still be cleared of blockages. Any bends should be limited to positions in or close to inspection chambers or manholes (see paragraph 2.49) and to the foot of discharge and ventilation stacks. Bends should have as large a radius as practicable.

2.49 Siting of access points - access should be provided at the following points:
a. on or near the head of each drain run, and
b at a bend and at a change of gradient, and
c. at a change of pipe size (but see below if it is a junction), and
d at a junction unless each run can be cleared from an access point (some junctions can only be rodded through from one direction).

As far as I can see I am meeting these requirements, but as I said any further advice very welcome.

Phil

 

[Hugh Jaleak]

I'd be more concerned right now about chopping lumps out the exterior wall to get the proposed pipework in. If it is a former external wall, no doubt it is still supporting something.

 

[philrosenberg]

No chopping required. The builders took out the necessary brickwork and put a lintel in for the concealed cistern. The new stack will fit in that cavity.

 

[Hugh Jaleak]

Still struggling to visualise exactly what it's going to look like, but several points. The AAV (Osmavent), should be above the spillover level of the highest appliance, in this case, the basin.

You can do as you propose, but bear in mind if that short run from the WC pan does block up it'll be a pan removal job and could get messy. Any way of getting a straighter run from pan to stack, even if you need to drop down first before going horizontally?

Also the run to the washing machine, could be do in 50mm across the floor, reduce to 40mm above floor level, but provide a rodding eye to allow access to the 50mm underfloor.