The basics of waste-water plumbing… how many stacks?

[Dreadnaught]

Where do I need a slab penetration for a stack?

 

I have this cluster of waste appliances (see diagram). Can I use a single stack for eveything or do I need multiple? And if so, where should it go?

 

I have read Part H but I am still working out how things are implemented in practice. 

 

I suspect there is much wrong with this guess:

 

Edited December 22, 2019 by Dreadnaught

[PeterW]

I wouldn’t do that with one - I would put at least 2 where the arrows are - you have 4m runs which really need to be in 50mm to be on the safe side, especially with showers etc 

 

[joe90]

I was advised by the welsh wizard (aka @Nickfromwales ) to make runs for bath,shower,basins under floorboards in 50mm to avoid crud building up.

Edited December 22, 2019 by joe90

[Stewpot]

I would guess that long branches like that are going to syphon as the water flowing down them heads to the stack. Air-admittance valves may solve this - I'd put one near the washing machine, the bathroom basin, and the top left sink. But I dunno how that squares with the regs.

[Ed Davies]

Why would you have a stack in the house at all, rather than just AAVs? I'd think saving the roof penetration by keeping any needed stack outside would be well worthwhile.

[Dreadnaught]

27 minutes ago, Ed Davies said:

Why would you have a stack in the house at all, rather than just AAVs? I'd think saving the roof penetration by keeping any needed stack outside would be well worthwhile.

 

Oh, by stack I meant a penetration through the concrete-raft (slab) foundation (i.e. the floor) by soil pipe which connects to an underground foul waste-water drain. I didn't mean an SVP (soil vent pipe). Did I use the wrong term?

 

(Its a modern bungalow so only a single floor.)

Edited December 22, 2019 by Dreadnaught

[Gone West]

4 hours ago, Dreadnaught said:

I suspect there is much wrong with this guess:

I don't think there's that much wrong with it. I would probably do something similar with a 110mm AAV in the loft on top of the stack and a 50mm AAV where the washing machine is. I did go a bit OTT here fitting several AAVs to build in a bit of redundancy is case of failure. The green is 110mm and blue 50mm pipe.

 

[Temp]

Can you post a drawing of whole house? Usually best not to run drains under the house if possible. Most builders aim to have the 110mm from WC exit the house by shortest possible route and then run it around outside the house to join them up. So they draw a line from WC to nearest outside wall and put stack there. Then run smaller pipes to that stack.

 

The strategy doesn't always suit so it's not cast in stone. A drawing showing the house in relation to the sewer in the road and which way the land slopes would help us comment.

 

Pay particular attention to the pipe runs for showers. If you want a low profile shower tray with no plinth this should be 2" pipe and have the right falls and as few bends as possible.

 

At the bottom of a stack you should use a large/long radius bend to turn the flow from vertical to horizontal eg not regular short bend. Example..

 

https://www.travisperkins.co.uk/plastic-drainage/osmadrain-double-socket-long-radius-bend-87-5-110mm-4d581/p/710624

 

Take care with the ground floor WC. Many people find they have the pipe coming up through the floor in the wrong place - eg too near or too far from the wall or too short. I recommend bringing it up in the corner of the room and building a stub/short stack with AAV. Then you can put the WC anywhere and run 110mm from it to this stub stack in boxing. Perhaps not as pretty as getting it exactly right but less prone to error. If you have space a false wall looks better than boxing. You can also hide the cistern in it you want or go for a wall hung WC. If it's not full height the false wall also provides a shelf to put stuff and possibly cupboard space.

Edited December 22, 2019 by Temp

[Dreadnaught]

Thanks @Temp. Here you go … As you can see, I don't think I can avoid having the drain run under the house.

 

I fully agree with having everything you said, including having the stack in the corner and using a radius bend.

 

As I plan to be building my own partition walls throughout (using MF), I intend to build-in the wall-hung WCs. At Stack 1, the wall-hung WC will protrude into the neighbouring plant room. At Stack 2, I will do as you suggest and box it in with a half-height false wall with a useful shelf atop.

 

Edited December 22, 2019 by Dreadnaught

[Temp]

Aside: If Building Control are like mine they may want stack 1 to be open vented above the roof but say stack 2 can have an AAV. This isn't what the regs say. I believe both can be AAV if nearby houses have open vents. Its just some BCO are die hards and you have to pick your battles.

 

I think your proposed routing will work. If you or BC are concerned about the length from stack 1 to the IC you could put another IC in the corner of the L - Something like drawing below (with or without the other IC I added further south).

 

I'd be tempted to move the stacks nearer the shower wastes. Shower waste outlets are lower than WC wastes so they can actually be harder to run. The connection from the shower into the stack may have to be in the slab so needs planning now if you want to avoid a plinth under the shower tray or chipping the concrete away from around the stack. If you plan to have deep insulation above the slab it might be all fit in that but worth making a cross-sectional drawing showing the shower tray, waste, pipe falls and actual connection into the stack for shower and ditto for the WC.

 

We had some difficulty with the shower waste to stack connection in one of our bathrooms. The shower waste has to drop down into a cupboard in the room below and then connect into the stack lower down. There wasn't room between the WC connection to the stack and the floor. This sort of issue is harder to fix in a bungalow.

 

The regs also specify a minimum height from the bottom of the large rad bend to the lowest connection into the stack - so check the large rad bend will be deep enough in the ground to allow a low connection for shower.

 

Moving stack 1 to the south would mover it nearer the shower and should make the above a bit easier but not by much  Not shown but you could also consider moving stack 2 south against the southern wall in the corner of the cupboard of master bed for same reason.

 

 

 

 

 

 

Edited December 22, 2019 by Temp

[Dreadnaught]

Thanks @Temp. That's really helpful. I think the shower waste also explains why @PeterW suggested a second stack next to the shower (I was puzzling over it).

 

On the 1-in-10 rule for SVPs, when I am next on site I am going go around the neighbours and see if I can spot any other local SVPs. The nearest boathouse has just been rebuilt. I hope that they will have one. 

 

On a related point, I recall a while ago that @PeterW implied that the waste from a washing machine was uniquely useful for keeping the drains clean. The regular outflow of soapy water (often containing digestive enzymes too) was ideal for the purpose. I was therefore attracted by the idea of a single stack with the washing-machine waste-water flowing past the WC. But I now realise that the longer run from the shower might then be a problem.

 

I will now pay close attention to the shower wastes (both of them). 

And I assume I should also pay attention to the bath drain. Not as low as a shower but still quite low, especially as I plan to have a freestanding bath.