# Which soil pipe type to use under suspended ground floor



## chris_d (21 Aug 2010)

Lets play 'spot the self-builder' again....

I am led to believe that brown PVC soil/drainage pipe has chemical stabilizers to prevent it being attacked by acid in the soil/earth and that grey/black soil pipe has UV stabilizers to protect it from sunlight. Therefore, I believe that brown should be used below ground and grey/black above.

Now, here is my dilemma: What should I use in the 150mm air gap (void) beneath a suspended concrete ground floor? In my case, the ground beneath the void is exposed earth.

For plumbing convenience, I'd like to use grey pipework as the wider range of fittings makes it easier to achieve the interconnect I require but I'm worried that the BCO will demand to have brown pipework given that it will sit just a few inches above earth that could heave and hence come in contact with it.

I was proposing to use 110mm brown pipework from the external manhole through the foundation wall and just into the void then changing to a 110mm grey trunk pipe run from which there will be:
- two separate 50mm T-junctions to the kitchen sink and dishwasher;
- a 110mm/50mm multi-junction to a toilet and shower tray/basin;
- final 90 degree bend up to a roding access point and then a stack pipe to the first floor bathroom.

My preference to use grey pipework is based on the convenience offered by the 50mm junctions for the sinks, dishwasher and shower; I'm not aware of the availability of 50mm brown pipework or junctions.

So what does the collective experience of UKW suggest? Should I either:

1. proceed as discussed above;
2. or use 110mm brown pipework throughout and just live with the inconvenience and expense of running 110mm pipe everywhere including the extra junctions this entails.

The BCO will be inspecting whatever I do on Monday.

Thanks,
Chris


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## Digit (21 Aug 2010)

Brown is not only more corrosion resistant than grey it is also stronger to withstand the weight of soil compaction above.
In voids I have used grey without planning difficulties.

Roy.


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## chippy1970 (21 Aug 2010)

On all the new builds we do we have suspended block and beam floors and the groundworkers always use the brown pipes this then comes up through the floor where the plumbers take over and it changes to grey soil stacks rising in several places around the house, so only the under floor is in brown.

Hope this helps

Chris


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## Jake (21 Aug 2010)

My understanding is they are all identical, save for the UV protection in the black/grey/white ones. 

So, AFAIK it doesn't matter apart from brown is quite a bit cheaper because the UV protection additives are expensive.


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## jasonB (22 Aug 2010)

Do you have enough fall? a 150mm void will only allow 40mm of fall so your run can't be that long.

Personally I'd run it in brown with a bend taking it up into the kitchen and then fit a 110-50 adaptor into the end of that toi take the kitchen wastes. If you want to make the 50mm connections under the floor then just use a 110 junction (Tee) with the same adaptor in the branch.

Jason


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## Doug B (22 Aug 2010)

Jake":2he9byw8 said:


> My understanding is they are all identical, save for the UV protection in the black/grey/white ones.
> 
> So, AFAIK it doesn't matter apart from brown is quite a bit cheaper because the UV protection additives are expensive.




Yep, spot on my understanding as well.


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## chris_d (22 Aug 2010)

Thank you all for replying.

So, given that I don't care that grey fittings are slightly more expensive and that Doug, Jake and Roy believe that grey can be used in this application then I shall use predominantly grey fittings.

I assume that the site work that Chris (Chippy1970) described using brown was done so on the basis of cost rather than regulation.

Jason: I can actually get a fall of 1:62 and Part H of the Building Regulations permits a minimum gradient of 1:80 for 100mm internal diameter pipe where the peak flow rate is >1 litre/second and there is at least one WC. The regulations also suggest that a single dwelling will have a peak flow rate of 2.5 litres/second. Also, I shall follow your suggestion to use a 110mm T to the ktchen and reduce down above floor level.

Thanks,
Chris


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## Carlow52 (22 Aug 2010)

1:80 is fine in theory but if you can don't go that close as its pretty tricky to ensure the grade is 1:80 all the way along: pipe will need to be supported properly. 1:60 more forgiving, 1:40 even better

burrs in joints will catch paper easier at 1:80.

While I am pretty certain you mean it already, ensure the basin and shower tray have 2 separate connections to the vented stack


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## chris_d (22 Aug 2010)

Carlow52":2fexjsc7 said:


> While I am pretty certain you mean it already, ensure the basin and shower tray have 2 separate connections to the vented stack



Thank you for sharing the benefit of your experience with us Carlow. I am indeed using two separate 40mm connections for the shower and basin but if my interpretation of Part H is correct then I believe that they can be joined together provided that 50mm ID pipework is used from their junction back to the main stack.

Cheers,
C


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## Carlow52 (22 Aug 2010)

Glad to offer some non ww ideas [ until my new bandsaw arrives  ]

Not familiar with your actual regs, the risk that one is trying to avoid is that the water flow from either basin or shower being such that it will suck the water out of the other traditional S or P trap, it is a common problem with baths and basins due to the increased flow from the bath.

Good luck with the project


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