Service penetrations through raft foundation

[Russdl]

I need to finalise this for our timber frame company prior to them installing the raft foundation (they will also site the service ducts and drains).

 

I understand that mains water needs to come in through a 110mm  duct/drain pipe to allow space to insulate the main. I want water to go back out again to a garage and/or an accumulator that I can isolate from inside the house. Can both of these water runs fit in the one 110mm duct, or do they have to have one each? Is there a more intelligent way to do it?

 

I understand that mains electricity can come in via a 50mm duct. Can it also go out through the same duct ( to the garage etc) or do they need separate ducts, one in, one out? 

 

What about BT, (we weren't going to bother but nothing else is available and the 5G option using Huawei equipment is starting to look dodgy). I presume that needs its own duct and can't share with the electricity?

 

Finally, as a belt and braces option, I'd like to put a spare duct in for a (potential) future ASHP, or AirCon. Would that be 110mm as well?  And how would I seal it in a way that I could reopening at some later stage?

 

 

[Jeremy Harris]

You can probably get two runs of MDPE in a  100mm duct OK, as minimal insulation is needed, as the ground under the slab won't ever drop below zero around here (it'll sit at around 8°C). 

 

If your mains supply is coming in from an external meter cabinet, then it needs to be 25mm² SWA, which is pretty hefty.  I ran mine in a 100mm duct, just to make cable handling a bit easier.  You could probably run another couple of runs of cable in the same duct OK if it's 100mm.

 

BT require that their cables are run in their own grey Duct 56, which they should free issue on request.  It's a rigid duct system, so you need to request a hockey stick to bring it up through the slab.  You cannot put data/telecomms cables in the same duct as mains cable.

 

100mm duct should be OK for running a couple of pipes for an ASHP, and ideally you'd also run a  cable duct for this as well, perhaps.  Sealing is pretty easy, just screw up a ball of chicken wire to fit tightly inside, thread a bit of hefty fence wire through it and secure it well.  Push the ball down into the duct, with the bit of fence wire poking out, then fill with expanding foam.  The chicken wire stops rodents chewing into the foam and the bit of fence wire allows the plug to be pulled out at some future date.  Do this both ends of any spare open ducts.

[vk108]

This is my list of things in the slab. But I am yet start my build though...

 

1. hockey stick for mains.

2. water to plant room

3. gas to kitchen

4. grey telecom to hall

5. two svp in the walls for first floor( position checked)

6. downstairs toilet svp

7. plant room svp

8. kitchen island svp

9. kitchen island hot and cold supply(insulated)

10. kitchen Island power and one spare 25mm duct to island(you never know)

11. two 63mm to garage

12. two 63mm to house

 

[Russdl]

  On 08/04/2019 at 10:14, JSHarris said:

100mm duct should be OK for running a couple of pipes for an ASHP, and ideally you'd also run a  cable duct for this as well, perhaps.

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Good thinking re a cable duct for an future ASHP, I presume the cable couldn’t run down the same duct as the ASHP pipes?

[Russdl]

Did I read somewhere that BT can't be bought up through the slab?

[Jeremy Harris]

  On 12/04/2019 at 09:35, Russdl said:

Did I read somewhere that BT can't be bought up through the slab?

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No, it's fine to run a Duct 56 hockey stick up through the slab, it's what I did.  No problem at all as far as BT Openreach are concerned, although their rules have changed and that caught me out.

 

They had changed the rules some time ago, so that any new build was supposed to have an external junction box (a BT66) to terminate the incoming cable, with another cable going from that inside the house to the master socket.  I duly installed a BT66 on the fence where our meter box is, and ran Duct 56 in from the box at the base of the pole to that, then another run of Duct 56 from there under the slab and up into the house.  When the chap came out to connect it all up he told me that they no longer required the external connection box, and it would have been better if I'd run the Duct 56 straight in from the base of the pole to the house.  Sometimes you can't win as far as BT Openreach are concerned; I'm convinced that they make up rules as they go.

[Big Jimbo]

  On 12/04/2019 at 09:43, JSHarris said:

 

No, it's fine to run a Duct 56 hockey stick up through the slab, it's what I did.  No problem at all as far as BT Openreach are concerned, although their rules have changed and that caught me out.

 

They had changed the rules some time ago, so that any new build was supposed to have an external junction box (a BT66) to terminate the incoming cable, with another cable going from that inside the house to the master socket.  I duly installed a BT66 on the fence where our meter box is, and ran Duct 56 in from the box at the base of the pole to that, then another run of Duct 56 from there under the slab and up into the house.  When the chap came out to connect it all up he told me that they no longer required the external connection box, and it would have been better if I'd run the Duct 56 straight in from the base of the pole to the house.  Sometimes you can't win as far as BT Openreach are concerned; I'm convinced that they make up rules as they go.

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Nice to not have to have the external box anymore. Just something else to get wet, or bashed in the future.

[Russdl]

@JSHarris Thanks again for the comprehensive reply Jeremy.

[Jeremy Harris]

  On 12/04/2019 at 09:45, Big Jimbo said:

Nice to not have to have the external box anymore. Just something else to get wet, or bashed in the future.

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I wholeheartedly agree, I just wish that we hadn't backfilled the trenches and laid a stone path over the top when I was told the damned box was no longer needed...

[Big Jimbo]

  On 12/04/2019 at 09:48, JSHarris said:

 

I wholeheartedly agree, I just wish that we hadn't backfilled the trenches and laid a stone path over the top when I was told the damned box was no longer needed...

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It's funny how so many companies make such a fuss, but the actual guys that come to do the work are happy with a cup of tea and a bit of cake.

[bissoejosh]

  On 12/04/2019 at 09:43, JSHarris said:

 

No, it's fine to run a Duct 56 hockey stick up through the slab, it's what I did.  No problem at all as far as BT Openreach are concerned, although their rules have changed and that caught me out.

 

They had changed the rules some time ago, so that any new build was supposed to have an external junction box (a BT66) to terminate the incoming cable, with another cable going from that inside the house to the master socket.  I duly installed a BT66 on the fence where our meter box is, and ran Duct 56 in from the box at the base of the pole to that, then another run of Duct 56 from there under the slab and up into the house.  When the chap came out to connect it all up he told me that they no longer required the external connection box, and it would have been better if I'd run the Duct 56 straight in from the base of the pole to the house.  Sometimes you can't win as far as BT Openreach are concerned; I'm convinced that they make up rules as they go.

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This is interesting. I've just had my duct delivered and laid but was told that the duct must finish externally and cannot pass through the slab. I questioned this several times to receive the same answer. Perhaps it depends on the inspector in your area. I'm still tempted to try and bring it through the floor and hope the local engineer doesn't mind but it would be a pain if on connection day I had to reroute.

 

 

[Russdl]

  On 12/04/2019 at 09:52, bissoejosh said:

was told that the duct must finish externally and cannot pass through the slab

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Ah. Maybe that is another Openreach change since Jeremy was connected? I had read something similar but couldn't recall where, hence my earlier question.

[Jeremy Harris]

  On 12/04/2019 at 10:17, Russdl said:

 

Ah. Maybe that is another Openreach change since Jeremy was connected? I had read something similar but couldn't recall where, hence my earlier question.

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Anything is possible with Openreach...

 

I was sent a specification for installing Duct 56 on a new site, by the Openreach main office.  That stipulated that a new installation had to have an external termination box, a BT66.  There was no restriction on what I chose to do from the BT66 into the house, so I opted to just run Duct 56 under the slab and up where I wanted the cable to come in.  I also provided a length of underground (gel filled) cable (to the Openreach spec) for the run from the house to the external BT66.  I just left excess cable looped up at both ends, as the terminations have to be made by Openreach.

 

It was only when the Openreach chap came around to connect us up that I was told that I'd wasted my time fitting the BT66 externally, as they would have been happy to run a  single length of cable from the base of the pole, along a single length of duct and into the house.  By that time this wasn't practical to do, as the trenches were filled and a path laid on top, so I just had two vertical hockey sticks poking up under the fence where the BT66 is fitted.

 

It's quite possible that the chap wiring things up would have been happy to just ignore the spec that I was given by the Openreach office.

[Russdl]

  On 12/04/2019 at 10:27, JSHarris said:

Anything is possible with Openreach...

 

I was sent a specification for installing Duct 56 on a new site, by the Openreach main office

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I shall continue trying to get in touch with them and see what is said.

 

Standby...

[JanetE]

Be aware that if you want the ASHP insulated pipe to go under your raft foundation you will be hard pressed to fit this in the 110mm pipe.  We had a hell of a job getting the pipework through, partly because we used a 90° bend as opposed to a slow bend to exit into the service room and also because the ASHP insulated pipe is not very flexible.  We ended up having to fit two long flexible connectors to get it round the last bend and also we had to strip off the outer flexi casing and a layer of insulation to get it through the duct.

Edited April 12, 2019 by JanetE
Adding pics

[Russdl]

@JanetE Very useful information, thanks very much. 

[bissoejosh]

I had been planning to fit ASHP pipe through the walls and have left a section uninsulated temporarily for access. Is this a bad idea? It isn't too late to add through slab (beam and block in our case) ducts if it makes a significant difference.