Pumped waste design for kitchen sink and dishwasher waste

[Adsibob]

Our rear extension is sunk into the ground by about 40cm (planners' requirement, not ours). As the original house is already about 80cm or 90cm below the road and as we are having our kitchen sink and dishwasher at the back of the rear extension, we are going to need a pump to get the waste water from the kitchen sink and dishwasher up to the sewer on the road. I'm just trying to figure out what design considerations I should factor in. We are keen that the pump is quiet but appreciate that these things can never be silent so we were going to place the pump as far away from the kitchen as we can get away with. At the moment, the idea is to take the waste water to the side passage of the house and house the pump underground, in a chamber in the side passage that is covered with a manhole cover. Should I be fitting a back-up pump as well in case the primary one cuts out / dies, or is that only necessary for a toilet? Alarm system to notify me of any issues? Any other recommendations? Is Saniflo the market leader for quiet pumps or should I be considering other brands as well? Any issue with it being outside during a cold patch of weather in winter. Say if the temperature drops to -10? We live in London, so that's rather unlikely, but not unheard of.

[markc]

How deep/shallow is the sewer? If the kitchen floor level is 1300-1400 below road level, the kitchen waste would only be a metre or so below so you may be ok dependant upto length of run to get there.

[Adsibob]

3 hours ago, markc said:

How deep/shallow is the sewer? If the kitchen floor level is 1300-1400 below road level, the kitchen waste would only be a metre or so below so you may be ok dependant upto length of run to get there.

Not sure how deep it is but my builder told me we need a pump and I'm not doubting him because we need to travel about 22m or 23m to get there, so no chance of doing that without a pump for about half of the way.

[Adsibob]

Another issue is the extent to which the waste water pipe needs to be serviceable. Our thinking was to install it as shownin red on this drawing, with the pipe going behind the kitchen cupboards for about 4m before travelling through the cavity wall where it would then go underground to the chamber where the pump is. Assuming we can pull out the kitchen cupboards to service it, and there are a couple of access points for rodding, is this a good idea? I know it would be much easier to just go outside, but this area of the rear elevation is a bit of a feature so we rather not have a pipe on show  there.

 

 

 

[Nickfromwales]

Builders feelings set aside, what is the level of the invert at the road to where you need to discharge from? You’re appliances can discharge up high, like 600mm off finished floor level. Can’t they then just meet a spur off the existing drains? 

[Adsibob]

Okay, had a chat with the builder today: it MIGHT be possible to avoid a pump and have a gravity system. He’s going to try to set that up. Query about having the kitchen sink/ dishwasher water waste pipe predominantly internally: will I hear the water trickling down the pipe? Or will the kitchen base units which conceal the pipe, also muffle any sound?

[Dave Jones]

a pumped chamber isnt the end of the world at all. you wont hear it. They come with an alarm should the pump fail.

 

Before you do that, have the builder bring the laser and laser from the nearest sewr invert to your house and add 13mm per M is ifs close then you are allowed to use 1/pipe diameter.

[PeterW]

1 hour ago, Dave Jones said:

Before you do that, have the builder bring the laser and laser from the nearest sewr invert to your house and add 13mm per M is ifs close then you are allowed to use 1/pipe diameter.

13mm/m is 1:76 so near as 1:80, which is in the regs

 

1/pipe diameter for standard pipe is 1/110mm or 9mm/m which won’t pass as it’s 1:110 so is nowhere near regs.
 

There are options - if you want to go to that level then you have to go to 160mm pipework which has a maximum gradient of 1:150, but it’s expensive and getting 160mm sewer connections becomes problematic as you cannot breach cut a sewer pipe with a 160mm saddle unless you have a minimum sewer diameter of 350mm (based on STW and TW minimum requirements) you could be into blocking and over pumping to put branch connections into the sewer which will be very expensive ..!! It will make a pumping station look very cheap !!

 

 

[Adsibob]

I’m confused, I thought the necessary fall ratio was 1:40 not 1:80 ???

[Carrerahill]

3 minutes ago, Adsibob said:

I’m confused, I thought the necessary fall ratio was 1:40 not 1:80 ???

It should be between 1:40 and 1:110. So PeterW was meaning it is "within" the regs.

 

 

Edited June 16, 2021 by Carrerahill

[PeterW]

6 minutes ago, Carrerahill said:

It should be between 1:40 and 1:110. So PeterW was meaning it is "within" the regs.

 

 

1:110 isn’t allowable in the E&W regs for 110mm pipe. 

[Carrerahill]

17 minutes ago, PeterW said:

1:110 isn’t allowable in the E&W regs for 110mm pipe. 

Thought were were talking sink wastes here. What is the min. for 110? 1:80?

 

Range 1:40 to 1:80?

 

 

 

 

Edited June 16, 2021 by Carrerahill

[Mr Punter]

I would run the waste right to the end of the kitchen units in 40mm.  It looks like there is a void or some insulation behind anyway.  Run it to a decent fall.  I don't know where the drain is outside in relation to your plan.

 

23m is not a particularly long run.   if you know the invert of the drain we can let you know if you can let gravity be your friend.

[Adsibob]

3 minutes ago, Mr Punter said:

I would run the waste right to the end of the kitchen units in 40mm.  It looks like there is a void or some insulation behind anyway.  Run it to a decent fall.  I don't know where the drain is outside in relation to your plan.

 

23m is not a particularly long run.   if you know the invert of the drain we can let you know if you can let gravity be your friend.

Will I be able to hear the trickle of the water from the sink, or can i just insulate the pipe? Not sure i will have much space for insulating a 40mm pipe.

[Mr Punter]

I don't think the noise of the water will be an issue at all.  More likely to hear the water as is goes down the sink waste, not once it is in the pipe and running steadily.

[Nickfromwales]

3 hours ago, Adsibob said:

Will I be able to hear the trickle of the water from the sink, or can i just insulate the pipe? Not sure i will have much space for insulating a 40mm pipe.

It’s that compromise or a pump   Take the compromise ! 
 

 

3 hours ago, Mr Punter said:

I don't think the noise of the water will be an issue at all.  More likely to hear the water as is goes down the sink waste, not once it is in the pipe and running steadily.

+1

 

Forget the above mention of 110mm pipe, and just run it in 50mm all the way with T’s and cleaning ( rodding ) eyes at each significant point or change of direction instead of bends. All bends need to be bends NOT elbows eg swept. 23m will be fine. 

[Adsibob]

Thanks, this is all helpful stuff. I don't think I have space for a 50mm pipe, but definitely have space for 40mm. Is there a big difference in performance/serviceability between 50mm and 40mm? I think the regs require a minimum diameter of 30mm (table 2, page 9 of this: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/442889/BR_PDF_AD_H_2015.pdf)

[Nickfromwales]

You’re not really supposed to run 32 or 40mm more than 3m in normal circumstances, but when adversity strikes you can mitigate against ‘risks’ as per the above ( 50mm pipe and plenty of cleaning access etc ). 
Theres no way in hell that you can go to 32mm pipe for this, and I wouldn’t do it in 40 for more than 6m before upsizing to 50. 
What’s the issue with locating the 50 all the way?
 

[Adsibob]

18 hours ago, Nickfromwales said:

What’s the issue with locating the 50 all the way?
 

The units I'm buying have a 42mm service void at the back. So i guess i could set them 8mm in front of the wall and create a 50mm gap that way. Or chase into the wall, but I rather not as that will diminish my insulation.

[markc]

1 minute ago, Adsibob said:

The units I'm buying have a 42mm service void at the back. So i guess i could set them 8mm in front of the wall and create a 50mm gap that way. Or chase into the wall, but I rather not as that will diminish my insulation.

Unless your walls are absolutely perfect you will end up with at least some of the units pulling forward anyway. 10mm forward is nothing and wont affect the worktop

[TonyT]

Pull the units forward and put a decorative end panel to hide the gap.

 

 

 

[Nickfromwales]

3 hours ago, Adsibob said:

The units I'm buying have a 42mm service void at the back

So with that and the plasterboard channelled you you’d have 56mm to play with? More if it’s plastered plasterboard. 

Edited June 17, 2021 by Nickfromwales

[Dave Jones]

On 16/06/2021 at 16:14, PeterW said:

1:110 isn’t allowable in the E&W regs for 110mm pipe. 

 

link to where it says that ?

[PeterW]

16 hours ago, Dave Jones said:

 

link to where it says that ?

Building Regulations Part H Approved Document (2015)

 

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

 

Sections 2.29 onward, notably Diagram 9 and Table 6, page 15 and page 16. 

 

All clearly stating the minimum gradients. 

[Dave Jones]

On 20/06/2021 at 11:23, PeterW said:

Building Regulations Part H Approved Document (2015)

 

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

 

Sections 2.29 onward, notably Diagram 9 and Table 6, page 15 and page 16. 

 

All clearly stating the minimum gradients. 

 

not seeing that anywhere for 110mm pipe and it says recommended for 100mm pipe.

 

1/pipe diameter is accepted by severn trent.

Edited July 13, 2021 by Dave Jones