Foul Drainage design guidance please

[SuperJohnG]

Due to undertake the foundation shortly and the drainage design needs figured out so I can finalise the drawings and then no last minute decisions with the groundworkers or hold ups. 

 

I have an insulated foundation and hence drainage need to go under the slab where required, I am trying to minimise this but have a few options currently I wanted some input on to ensure I avoid problems that other may have encountered, it's a large open plot with fairly low invert levels due to a burn which I'll discharge into. If i need to I will use a pumped tank to remove the worry of not having good enough falls. 

 

I have attached a section of the site plan showing house and foul and surface water discharge for reference. 

 

 

 

I have a number of drains on the ground floor:

1) Kitchen sink(plus optional drain underneath island for future changes if we wanted to put a sink there).

2) Gully trap outside kitchen window

3) Downstairs shower room including toilet, basin and shower.

4) Soil vent pipe which is located in a w)all within the downstairs shower room

5) Utility room sink drain (does WM too)

6) Plant room drain - covers safety reliefs, MVHR condensate etc. 

 

my question is what layout works seems to work best, and how best to tie some of these together. I.e. In the downstairs bathroom, how do I tie the toilet, basin, shower and soil vent pipe together below the floor do I drop down a 110mm for all? or try hide them in a wall, then tie all to SVP or what seems best? I've shown my drgs below, with an overall view of house an positions, then a detailed view of the respective drainage run for each option.   

 

Foul runs are in dark blue

 

Option 1: Architect suggested layout, no plant room drain. 

Option 2 - My first layout, keeps the runs straight and gets them out from under the slab. Punches straight out from utility picking up plant room and then straight runs outside into an IC to collect everything then flow to treatment plant. Good straight runs and allows Rodding eyes to access everywhere. 

 

 

 

 

Otion 3: My second option - removes outside run around hosue and ties it back under the slab from kithchen to downstairs wc. Short run, but a join underneath slab and difficult to add rodding eye at kitchen end. 

 

 

 

 

Option 2 for me seems to make the most  sense as it is straight easy runs and tied where possible outside the slab, I just need to check invert levels.  Does anyone have any input that would help? 

 

I've added the full pdf with all options of anyone is really really bored...

Drainage options Model update.pdf

[Russell griffiths]

Why are you worried about minimising pipe runs. 

Put them where you need them, don’t skimp on them because you think it will be a faff. 

 

I think i have somewhere in the region of 9 110mm pipes exiting under the house.

 

 

[PeterW]

Option 3 but get the main run much closer to the island so it’s just a bend and an oblique tee and run it all the way out to the outside wall and put a rodding eye on it. Same with the kitchen sink, out past the wall and a rodding eye. Where is the dishwasher ..?? 
 

And the plant room change of direction should be an IC rather than a tee and a rodding eye. 

[Oz07]

I'd go 3 but have a 3 way ic and don't bother trying to join toilet run to the kitchen sink run under the slab. More liable to give you an issue with inaccessible junction as opposed to 3 way chamber. You can get level chamber bases so this won't effect your invert heights. Osma do a good 1 piece 3 way level IC. 

[Oz07]

Also as Peter says taking that kitchen run out through the other side of house and popping a ridding eye on is a good shout. I've done that at mine. 

[SuperJohnG]

1 hour ago, Russell griffiths said:

Why are you worried about minimising pipe runs. 

Put them where you need them, don’t skimp on them because you think it will be a faff. 

Not so much minimising to about pipe runs, but more so pipe runs underneath the slab as I thought it would be best to have them out the slab?

I think what I  am trying to do here is find out where I need them and what is best. 

 

The burn runs from east to west , I previously had the treatment plant out to the west downstream as it made sense, but was struggling with the falls and then it made sense to put it out the back of the house as it was a shorter straighter run and less falls issues. Not bothered about saving a few pence on pipe, but I have a borehole to the north there to go in, plus a power to come in front the front. 

 

1 hour ago, PeterW said:

Option 3 but get the main run much closer to the island so it’s just a bend and an oblique tee and run it all the way out to the outside wall and put a rodding eye on it. Same with the kitchen sink, out past the wall and a rodding eye. Where is the dishwasher ..?? 
 

And the plant room change of direction should be an IC rather than a tee and a rodding eye. 

I was thinking this was the worst option. So get the main angled run between sink and island, then punch it straight out the wall outside? Not quite getting that. 

Dishwasher will be somewhere close to sink there - I am assuming pop the 110mm pipe up through the slab underneath kitchen unit then tie sink and dishwasher into it?

 

Plant room external - got it - why an IC instead of 90 with RE?

 

1 hour ago, Oz07 said:

I'd go 3 but have a 3 way ic and don't bother trying to join toilet run to the kitchen sink run under the slab. More liable to give you an issue with inaccessible junction as opposed to 3 way chamber. You can get level chamber bases so this won't effect your invert heights. Osma do a good 1 piece 3 way level IC. 

So do the 3 way IC where i have it, but just take kitchen connection straight outside? I do prefer to not have that connection underneath the slab. How do the level chamber bases differ compared to something else? Is it just that they are moulded with that small invert compared a normal chamber having a larger invert?

 

thanks for the replies so far. 

 

[SuperJohnG]

 Also, how do I tie this together through slab?

SVP obviously goes all the way through slab, the basin and toilet will be wall hung, hence the basin i can put waste down through wall and pop it into the SVP. For the toilet should I just actually build that section out make it wall hung and tie the waste directly into the SVP ?

 

Shower tray will be floor mounted, so we were going to add a drain below FFL, but I haven't selected the shower tray hence location is not set do I again drop a 110mm pipe straight down and connect below slab or in slab. Some of these things I feel should be obvious but not having done them it's good to understand best practice.  

 

[LA3222]

32 minutes ago, SuperJohnG said:

 Also, how do I tie this together through slab?

SVP obviously goes all the way through slab, the basin and toilet will be wall hung, hence the basin i can put waste down through wall and pop it into the SVP. For the toilet should I just actually build that section out make it wall hung and tie the waste directly into the SVP ?

 

Shower tray will be floor mounted, so we were going to add a drain below FFL, but I haven't selected the shower tray hence location is not set do I again drop a 110mm pipe straight down and connect below slab or in slab. Some of these things I feel should be obvious but not having done them it's good to understand best practice.  

 

I'm putting wall hung toilets in. With the down stairs toilet I'm going to build the stud out to hide the frame and SVP, ill run a horizontal pipe across from the toilet to drop into the SVP much like you propose her.

 

With this being a ground floor shower, bot sure how you'd tie that in, a low profile trap but then getting the fall. If you go for a deeper slab could you put a bit of formwork in to keep it clear of concrete?

 

Edited November 17, 2020 by LA3222

[SuperJohnG]

1 hour ago, LA3222 said:

With this being a ground floor shower, bot sure how you'd tie that in, a low profile trap but then getting the fall. If you go for a deeper slab could you put a bit of formwork in to keep it clear of concrete?

I think tanners were going to add a note. Would defo be easier just to add some formwork and then leave space for a low profile drain and run which could tie into the SVP.  Just getting it lined up again isn't it. 

[Oz07]

I placed my drain exactly where shower drain was. Some plumbers thought I was crazy but if you line it up you're ok. There's a JT vertical outlet trap which is the same outer size as pan connector  so can seal into drain with rubber off one of those. It is probably easier to use 2" sideways trap with shuttering and connect down into 110mm. Level IC have no difference in invert depth

https://www.jewson.co.uk/p/osma-drain-shallow-inspection-chamber-250mm-brown-PO4D960Z

[SuperJohnG]

I've done an update on this based on some feedback above, does this seem like a better option now @PeterW @Oz07. I'm hoping this captured what you guys meant about the Oblique tees, which I assume come off that main run, seems a little foreign to have those connections like that?

 

 

 

[Dan F]

It's advisable to avoid putting both toilets or kitchen sinks on branches,  anything else is OK. (according to NHBC anyway)  See attachment

 

Note also, that length of runs around the house will impact invert levels.  Your original option 2 looks the simplest, but your main drain at the front of RHS of he house as drawn will need to be somewhat lower.. which may be an issue. 

 

 

 

 

Y-junctions-in-drains-under-buildings.pdf

Edited November 23, 2020 by Dan F

[SuperJohnG]

@Dan F thanks for this. 

 

Stuff it - I've sacked off the island drain, it was just in the event we put one of those wee prep sinks in there some time in the future. But - I'm likely never going to do it and will likely be far too skint to do it! Final revsion maybe...

 

 

 

 

 

Edited November 23, 2020 by SuperJohnG
mistake

[Dan F]

@SuperJohnG  Leave the island drain in, it'll cost you nothing and leaves the option open!!  Why not this..

 

 

 

[SuperJohnG]

49 minutes ago, Dan F said:

@SuperJohnG  Leave the island drain in, it'll cost you nothing and leaves the option open!!  Why not this..

 

 

 

 

 

I may well do - just seemed to be causing hassle. It's just trying to remove those joins under the slab. 

[Dan F]

9 minutes ago, SuperJohnG said:

I may well do - just seemed to be causing hassle. It's just trying to remove those joins under the slab. 

 

We had three of these y-junctions under the slab.  Was no hassle and additional no cost.  We just ensured that toilets and kitchen sinks weren't on a Y-junction as per guidance I shared which seems very sensible.

- Kitchen island (just in case)

- UVC overflow

- Water-softender + ComfoPost

[Oz07]

Looks better now mate.

[Oz07]

The exceptions in link @Dan F posted allow y junction where there is a rodding point outside so I think you would be ok with either 4 or 5