Design of new soil system

[Jeremy22]

Hi there

We’re just about to add a timber frame first floor extension to our bungalow and I’m mapping out the waste and soil pipes. 
 

There are going to be three new bathrooms upstairs, all on one side, specifically to use the existing soil stack that is already there for the downstairs WC. 
 

Attached is my first draft of the design, can anyone see anything not right?

 

Thanks in advance

Jeremy

[PeterW]

I take it you’ve read this as a start point..??

 

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf

 

I don’t like opposing soil stacks and those would have to be full swept connections to stop cross flow. 
 

The flush may also cause your baths /showers to pull past the water seals as the waste from the WCs drop. 
 

I would make one or the other of those the other way up, and put the WC connections offset and below the floor - possibly the left one.  Then use the baths/showers to flush it through regularly.  

[Temp]

+1

 

I don't think 110mm opposed connections (eg for the WC) are allowed at all. See notes on diagram 2.

 

We find having two showers or baths on one narrow pipe causes more issues with siphoning. Eg one shower makes the other gurgle. If possible think about where you might add AAV later if you get an issue. For example on the left most shower waste, perhaps extend that pipe further to the left then up. Cap it off and add an AAV there if you get issues. 

[Jeremy22]

Yes, I’ve spent hours reading the regs documentation!

I thought opposing branches were OK if they have the same centre line and are swept? Otherwise why would all the manufacturers offer fittings?

Would the flushes cause water in the showers/bath/basins to drop when the stack is vented and they are on separate branches?

The branch for the showers etc was going to be 40mm but it can easily be 50mm

 

I was also thinking the right hand basin should go into the stack in its own boss rather than in the top of the 110mm with a clamp on boss as this would be neater. 

[PeterW]

Is this all exposed or internal ..??

 

And is it all boxed in as you’ve got access points on the shower runs ..?

 

Also worth having a look at BSEN12056 which has some better descriptive layouts, but if you can rework the outlets into swept tees you’ll save money and have a better running system in my experience. 

[Gone West]

1 hour ago, Jeremy22 said:

I thought opposing branches were OK if they have the same centre line and are swept

They are OK and that is what I used in my house. The BCO was quite happy.

[Jeremy22]

41 minutes ago, PeterW said:

Is this all exposed or internal ..??

 

And is it all boxed in as you’ve got access points on the shower runs ..?

 

Also worth having a look at BSEN12056 which has some better descriptive layouts, but if you can rework the outlets into swept tees you’ll save money and have a better running system in my experience. 

The majority is outside - falls from basins will be mostly inside before 'popping' out!

Can you explain the issue with access points on shower runs?

 

17 minutes ago, PeterStarck said:

They are OK and that is what I used in my house. The BCO was quite happy.

Thank you!

[joe90]

I think opposing swept joints are ok if you have enough distance from toilet to it, and I think you have. 

[Jeremy22]

11 hours ago, joe90 said:

I think opposing swept joints are ok if you have enough distance from toilet to it, and I think you have. 

Thank you

[Jeremy22]

@Nickfromwales what do you think?

[Nickfromwales]

1 hour ago, Jeremy22 said:

@Nickfromwales what do you think?

Same thing as to be expected.......

 

"problem, solved"

 

?

[Dan F]

Your diagram doesn't show pipe diameters.   Based on diameters/lengths of you branches for basins, these might need a secondary vent or anit-siphon trap potentially..

 

There is a table in building regs that talks about maximum branch lengths..

[Nickfromwales]

You will need to use a 15 degree or 30 degree bend out of that to rectify to the correct fall, or a variable 45 link as required.

If you have a vent to atmosphere then the traps will be fine IMHO, as long as every single piece of waste pipe under the floors is done in 50mm, and not 40mm anywhere until above and horizontal.

13 hours ago, PeterStarck said:

They are OK and that is what I used in my house. The BCO was quite happy.

Yup. I prefer the swept wherever possible but back in the day I fitted a good few like this without any 'known' issues.

[Nickfromwales]

4 minutes ago, Dan F said:

Based on diameters/lengths of you branches for basins, these might need a secondary vent or anit-siphon trap potentially..

50mm small bore runs will negate any further mitigation. It'll allow an air break, and as the horizontal runs are across the 3 items, there wouldn't ever be an opportunity for a vacuum to occur ( IMO lol ). I've done so many of these I've lost count. 

[Dan F]

48 minutes ago, Nickfromwales said:

50mm small bore runs will negate any further mitigation. It'll allow an air break, and as the horizontal runs are across the 3 items, there wouldn't ever be an opportunity for a vacuum to occur ( IMO lol ). I've done so many of these I've lost count. 

 

Yeah. Problem is when plumber puts 32mm in, ignores the length and then proceed to add lots of bends... ?

[Jeremy22]

Thank you everyone. 
 

All the horizontals will be outside (apart from the one in the third bedroom on the right where the shower is away from the wall), is that OK?

 

Grey waste horizontals in 50mm. Do the junctions into this need to be 45 degree or is swept OK?

 

Opposing 110 branches OK if they are swept (or do they need to be 45 degree as well?). 
 

@Nickfromwales where the WCs connect to the branch, is that where you say I need the 15 or 30 degree bend into the branch? It was that for the connection of the WC horizontals into the 45 degree branch in the stack? Do the WC connections work straight out of the back of the WCs?

[Nickfromwales]

On 19/03/2021 at 08:06, Jeremy22 said:

Grey waste horizontals in 50mm. Do the junctions into this need to be 45 degree or is swept OK?

Swept / regular is fine.

 

The 110mm branch I linked doesn't come to 87.5 degree like a regular branch would, so you'll need to install fittings into the branch, either side, to pick up each of the horizontal runs of 110mm so they have the correct fall.

 

On 19/03/2021 at 08:06, Jeremy22 said:

Do the WC connections work straight out of the back of the WCs?

Not sure what you mean, sorry? If you mean the WC's connecting immediately to the soil stack without dropping first, then yes, that's fine too, just make sure there is a distinct fall between the outlet of the WC and where the pipe turns towards the stack. If possible, for the middle WC with the branch, could you make that a 45 at the back of the toilet into a Y branch ( instead of WC straight into a T branch ) so the connection is truly swept? 

[Jeremy22]

8 hours ago, Nickfromwales said:

The 110mm branch I linked doesn't come to 87.5 degree like a regular branch would, so you'll need to install fittings into the branch, either side, to pick up each of the horizontal runs of 110mm so they have the correct fall.

Floplast do a swept double branch - could I use that and avoid needing additional fittings?

 

8 hours ago, Nickfromwales said:

Not sure what you mean, sorry? If you mean the WC's connecting immediately to the soil stack without dropping first, then yes, that's fine too, just make sure there is a distinct fall between the outlet of the WC and where the pipe turns towards the stack. If possible, for the middle WC with the branch, could you make that a 45 at the back of the toilet into a Y branch ( instead of WC straight into a T branch ) so the connection is truly swept?

I meant the connection out of the back on the WC bowl (the one at 190mm). So I can connect those to the branch without a drop into the branch? And the middle WC I should do that using a Y connection (so it will punch through the wall at an angle)?

 

[Nickfromwales]

2 hours ago, Jeremy22 said:

Floplast do a swept double branch - could I use that and avoid needing additional fittings?

If it doesn’t rectify you near to horizontal then no. Post a link to the fitting. 
 

2 hours ago, Jeremy22 said:

I meant the connection out of the back on the WC bowl (the one at 190mm). So I can connect those to the branch without a drop into the branch? And the middle WC I should do that using a Y connection (so it will punch through the wall at an angle)?

Yes, no drop needed but a fall will be required howsoever short the run ends up bring. Yes, exiting the wall at an angle. That is the unicorn, but I’ve done countless with a T branch without ever having an issue ( coupled with a fall to the stack and the stack falling to the SVP riser ). 

[Jeremy22]

 

2 hours ago, Nickfromwales said:

If it doesn’t rectify you near to horizontal then no. Post a link to the fitting. 

FLOPLAST 110mm Soil Ring Seal 92.5 Degree Double Branch - Grey

 

2 hours ago, Nickfromwales said:

coupled with a fall to the stack and the stack falling to the SVP riser

I'm being stupid - isn't the stack the SVP?

 

Because of the fall in the 110 branch, the middle WC will have to fall slightly to connect to the branch (compared to the right WC)

Edited March 21, 2021 by Jeremy22

[Gone West]

2 hours ago, Jeremy22 said:

I'm being stupid - isn't the stack the SVP?

You're not being stupid, yes, the arrangement you have is similar to mine, except I only have two toilets connected. The Floplast double branch you linked to is the one I used.

Edited March 21, 2021 by PeterStarck

[Nickfromwales]

On 21/03/2021 at 14:41, Jeremy22 said:

 

FLOPLAST 110mm Soil Ring Seal 92.5 Degree Double Branch - Grey

 

I'm being stupid - isn't the stack the SVP?

 

Because of the fall in the 110 branch, the middle WC will have to fall slightly to connect to the branch (compared to the right WC)

Stack to me is all of the 110mm pipework. Technically the SVP is only the piece of pipe above the last part of all the ‘wet’ 110mm stuff

eg the section that only takes the whiff up and away.

That branch has quite generous sweeps to it so should be fine. Others are very abrupt and would / could promote cross flow. If the horizontal parts of the stack ( branches ) have just the minimum fall then last nights byriani will not be doing 125mph when it gets to the vertical drop, so not such an issue anyway. 

[Jeremy22]

Just coming back to this to ask for further advice!  Based on my plan above, all the waste pipes are coming from internal sources (obviously) to external branches.  The trouble is, that means I need to drill a number of holes through the glulam that the whole of the upstairs sits on (it's essentially a ring beam around the house.

 

A better solution might be to take the waste pipes under the floor internally and then bring outside to join the soil stack.

 

Any ideas of the best way to do this?  Can I simply have a branch turning 90 degrees, coming out through the wall and going into a fitting on the stack?  And I have two opposing branches that both need to come into the stack.

 

Any help, as always, appreciated.

[Nickfromwales]

Drill one 50mm hole in from the 3rd boss on the fitting under the branch, then T everything waste wise in, inboard of the beam? At worst you'd be drilling 2x 50mm holes and then going through those 2 holes either side of the boss once per side?

If a BCO is involved you will need to demonstrate that you've drilled the beam in accordance with the MI's  Check before drilling !

Edited July 22, 2021 by Nickfromwales