Drainage pipes through ground bear slab with ICF rising walls on strip foundations

[Martin S]

Hi there

 

I am self-building our family home and have minimal fall from ground floor level down to the combined sewer to make a connection without having to rely upon a domestic pumping station.  We are building using ICF with strip footings and a ground bearing slab.  Our floor build up is as follows per attached details:

- nom. 25mm finish above screed level

- nom 50mm self leveling screed (assuming 50mm rather than 60mm drawn)

- Vapour control barrier/500 gauge polythene sheet over of nom thickness

- 165mm thick rigid PIR insulation

- Visqueen DPM of nominal thickness

- 150mm reinforced concrete slab

- 50mm sand blinding

- min 150mm hardcore

- min 225mm deep strip footings

 

I understand that it is usual for the drainage to penetrate through the rising wall above the strip footings with flexible connections either side to allow movement and that there is no need for lintels given ICF walls.

 

In terms of the floor build up what is the highest layer that I can penetrate the rising wall at, i.e. can the pipes penetrate down through the top of the floor, bend and penetrate through the rising wall within the hardcore, sand blinding, reinforced concrete slab or PIR insulation layer?  Reference to relevant building regs would be greatly appreciated in case I'm challenged by Building Control.

 

Thanks for your help.

 

Martin

 

[Mr Punter]

I am not a great fan of external floor level the same as internal FFL.  Possible damp problems.  Externally you need a bit of cover over the drains but  on your drawing they could be run just under the external slot drain.  If there is any way to avoid a pump station - even if fall is reduced to 1:80 - then do that.

 

Is this Polarwall icf?

[Martin S]

Thanks.  So I could break through the wall through the PIR layer and through the DPM lapping up the internal face of the rising wall? The DPM is Visqueen R400 Radon Membrane as also acting as a radon barrier with sump below.

 

Yes, using Polarwall.

[Nickfromwales]

I recently designed a foundation like this for a client that used Nudura ICF. Ditch the old school 150mm sub deck, lose the screed, add a bit more insulation, and raise the 120-130mm constructional slab up to become your finished internal floor.

This shows a near enough example, just has a different wall structure.

 

 

The UFH pipes go into the concrete layer, so I recommend going slightly thicker with ground bearing infill slab to give some extra cover over the UFH pipes which get zip=tied to the reinforcement steel (re-bar). At 100mm this can get quite close to top of concrete, so the one I detailed had 120mm iirc, vs the 100mm. Gives a hell of a long 'thermal time constant' / energy store which you can almost heat once per night at cheap rate via ASHP for running costs down as low as a few pence/kWh.

 

There are loads of examples of this being done here, so I suggest you do some searching on here before pushing any buttons, but your chosen method is not optimum for insulation, running costs, or practicality imho. 

Edited July 31, 2023 by Nickfromwales
sub deck not sun...

[Martin S]

Thanks for the feedback, I’ll take a look but in the meantime any feedback re the drainage gratefully received.  Avoiding need for a domestic pumping station is my main concern at the moment?

[saveasteading]

3 minutes ago, Martin S said:

Avoiding need for a domestic pumping station is my main concern 

Quite right, but the points above about levels are correct. Always build above ground level if you can.

Not only does it reduce damp and flooding risks, but also allows gravity to be your friend, assisting flow rate and increasing  drain depths.

 

Can you raise the house or lower the external area?

 

[Martin S]

Understood but seeking level thresholds for wheelchair access.  Unfortunately can’t raise house - had to dig down in the site to accommodate ridge height - and connecting into pre-existing combined sewer at a certain height.  Be great if, as a minimum, I could lay drain across sand blinding to gain its 50mm thickness and 150mm thickness of hardcore. If I could go across higher even better.

[Chanmenie]

As @Nickfromwales said lose the screed and put the UFH pipes in the slab, I did it slightly different in that I didn’t use mesh, I clipped the pipes directly to the PIR then used fibre reinforced self compacting concrete. 
You’ll save the cost of the screed and have room for more insulation 

[saveasteading]

And how much lower than the floor is your final drainage connection?

[Chanmenie]

11 minutes ago, saveasteading said:

And how much lower than the floor is your final drainage connection?

I brought my pipes in over the strip footing under the PIR but I have loads of fall to play with as the main is approx 1.6m below my finished floor 

Edited July 30, 2023 by Chanmenie

[Martin S]

Final drainage connection is 770mm below internal ground floor finish level but pipes need to run ~50m.

 

[Chanmenie]

2 minutes ago, Martin S said:

Final drainage connection is 770mm below internal ground floor finish level but pipes need to run ~50m.

 

So you need to start max 270mm down to give 1:100 fall which I believe is the min fall you can have.

Not ideal but you’ll have to have the pipes in the insulation layer 

[saveasteading]

1 hour ago, Chanmenie said:

1:100 fall

..is beyond many groundworkers' abilities. 

 For later of course, but you will have to check their abilities and understanding or 1. The pipes won't join.  2. It will be flat or uphill in areas and get blocked.

 

Also be aware that height is lost at turns in inspection chambers.

I think it is about 30mm but this could matter.

This all needs thinking through now.

[Chanmenie]

36 minutes ago, saveasteading said:

..is beyond many groundworkers' abilities. 

 For later of course, but you will have to check their abilities and understanding or 1. The pipes won't join.  2. It will be flat or uphill in areas and get blocked.

 

Also be aware that height is lost at turns in inspection chambers.

I think it is about 30mm but this could matter.

This all needs thinking through now.

Yeah certainly, I personally would not want a 1:100 fall, I’ve done mine at 1:60 

as you say very little room for error.

[Nickfromwales]

17 hours ago, saveasteading said:

Also be aware that height is lost at turns in inspection chambers.

You can use the min input and output and put adjustable bend / 15 / 30 / 45^o bends in and keep the same invert. It's usually only the branches that pick up the first few direct connections that will be affected, the downstream IC's can be in > out at the same invert.

 

Agree on 1:100 being a tall ask of most groundworkers, but there are some good ones out there that will do this properly and successfully. I've had to run soil pipe literally horizontal and zero fall for up to 5m (in a straight line, no bends) and you'll be surprised at how well the momentum gets you "out of the sh*t". Not advising this of course, but I kept that arrow straight, zero depressions, and it works still to this day, 15+ years later (my mates parents house). THis was to get rid of a Saniflow that was constantly failing (due to "user error" most times), and I just got away with it.

 

The pipe will need supports every 1200mm, made up of 6:1 concrete mix with 10mm aggregate, to create piers. This will allow you to level and flatten the pipe run perfectly. Use timbers driven into the ground to act as temporary 'brackets, every 1200mm, and then once dead on, you then fill with the concrete 500mm away from each timber bracket and leave to cure. Then remove the timbers and get to the pub. Be present for the back-filling and explain that this needs to be pea-shingle all the way back until you have 300mm of cover over the pipe.

 

Can defo be done with excellent results, I've done enough to know, but you'll first have to ask your BCO if he will allow a deviation from 1:80 by you demonstrating that it works (functions) and explain the methodology and how you've mitigated against future depression with the higher frequency concrete piers and complete back-fill with shingle.

[saveasteading]

It is easier to be precise when not in a deep trench. This won't be deep.

 

 

[Nickfromwales]

14 hours ago, saveasteading said:

It is easier to be precise when not in a deep trench. This won't be deep.

 

 

I didn't say it was easy  just it is doable. It's not the size of the dog in the fight, it's the size of the fight in the dog  

[ToughButterCup]

22 hours ago, Martin S said:

...

In terms of the floor build up what is the highest layer that I can penetrate the rising wall

...

 

Um....  you can penetrate the wall just below the level of the (say) toilet in the top floor can't you? Thats what everyone told us we should do. 

[Mr Punter]

You could run the last bit in 150mm pipe at 1:150 if the connection at the sewer end is sufficient diameter.