Conduits in concrete slab - making it all work

[Bancroft]

We're planning on a concrete slab foundation under an ICF build and I'm presently thinking about conduits required to run through the slab.

 

And the list seems to be growing daily!

 

I've got the basics like sewage out, and mains water and electricity in, but it's all the other stuff:

 

Into the house - ASHP, aircon (split system so essentially another ASHP just providing cool v hot), solar/battery, broadband/fibre.

 

Back out - electric gate power (and ethernet for video camera/security), lighting to garage, lighting to garden, water supply to external taps, power out to car charger.

 

And so the list goes on. (Let me know if anything crucial missed).

 

What's the best way to organise these without causing interference between different supplies or ending up with multiple conduits under the slab?

 

Clearly water and electric should be kept separate but can electricity, fibre and ethernet go through one conduit?  Is that a good idea? 

 

Could all electrical supplies go through one conduit or should they be split up?

 

Ditto ASHP and aircon plumbing.

 

Is it worth considering just a single electrical supply out and then putting another meter box in the garage to split all the external requirements from there?  

 

How have others approached this issue?

[Russell griffiths]

Power out for sewage treatment plant if you have one. 
don’t mix power and internet. 
don’t worry about multiple ducts, if you need them that’s it, you need them. 
all power in and power out can come up below the consumer unit, I have about 6 ducts there, then 3-4 more in the plant room for water in and ASHP in and out. 
you will need power out to the ASHP plus maybe cat 6 to control it. 
 Do a sketch of the house and some lines on it of every device inside and out and how each device will get either power or water to it or from it or both. 
I wouldn’t be surprised if you end up with 20 odd penetrations in the slab, don’t worry just get them in, and run a spare just in case. 

[Andehh]

Do not forget insulation size on the pipes!! We had a nightmare of a job pulling 4 x AC pipes through together with the insulation on. 110mm duct was stupidly ambitious, but narrowly managed to make it work.

 

Also bends disproportionately add to the resistance pulling things through.

[Nickfromwales]

5 hours ago, Bancroft said:

What's the best way to organise these without causing interference between different supplies or ending up with multiple conduits under the slab?

Don't be shy, the last M&E spec I delivered had about 17 different ducts for everything. Makes life soooo much easier at 1st fix etc, and for any alterations you may want to make downstream.

[Bancroft]

20 hours ago, Russell griffiths said:

Do a sketch of the house and some lines on it of every device inside and out and how each device will get either power or water to it or from it or both. 
I wouldn’t be surprised if you end up with 20 odd penetrations in the slab, don’t worry just get them in, and run a spare just in case. 

Yes, I'm expecting this as part of the architect's work but I just want to make sure I'm happy in my own mind before him and the builder start trying to bamboozle me!

 

Good point ref power for the sewage - had missed that one.

[Bancroft]

18 hours ago, Andehh said:

Do not forget insulation size on the pipes!!

Good point.  I expect size of duct is a balance between being as small as possible to reduce space and any heat loss, but big enough to not make it impossible to thread stuff through.

[Bancroft]

15 hours ago, Nickfromwales said:

he last M&E spec I delivered had about 17 different ducts for everything

Now got me thinking about what I might have missed!  My list seems small in comparison.

[Bancroft]

Some really helpful stuff here, gents, many thanks.

 

Feel better equipped to hold my own with the professionals.

[Russell griffiths]

List from my memory 

power in

power out to garage

power out to sewage plant

power in from solar

power out to car charger

telecoms in

cat 6 out to electric gates

power out to electric gates

cat 6 out for cameras 

power out front garden lights

power out back garden lights 

ASHP flow out

ashp flow return, could both be in single insulated duct

power to ASHP 

cat 6 to ASHP 

 

so 13-14 ish without thinking too hard. 
plus all your poo pipes. 
 

lots could change in your situation, 

sewage plant might be near the garage so could take power from there, the car charger could be on the side of the garage as well. 

[Nickfromwales]

12 hours ago, Bancroft said:

Yes, I'm expecting this as part of the architect's work but I just want to make sure I'm happy in my own mind before him and the builder start trying to bamboozle me!

The only real issue with rising penetrations through a slab is if it’s a block and beam. In this situation you need to avoid a beam. 

Structural engineers will have some “say” if you have all ducts together and it requires steel reinforcements being re-jigged, but a little bit of pragmatic pre-planning and dialogue will resolve this in a day. 

Tell your builder that this will progress at your pace, and will arrive at the end result that you want, and he will have to slow down accordingly. 

[trialuser]

My advice is that you talk to your air con installer at an early stage.

You will need to use an f-gas bod.

There are restrictions on the max pipework length to each indoor unit.

The insulated pipes (a pair to every indoor unit) are quite bulky, easily kinked, the insulation is easily torn (and then at risk of condensation forming) and should be a continuous length from external unit to the internal units.

[Bancroft]

11 hours ago, Nickfromwales said:

The only real issue with rising penetrations through a slab is if it’s a block and beam.

We're planning on full concrete slab at the moment so hopefully not an issue.

 

Not sure trying to hold the builder back will work.  I get the impression that once he gets going he's full speed ahead - which is another reason why I'm doing a bit of homework now.

[Nickfromwales]

3 hours ago, Bancroft said:

We're planning on full concrete slab at the moment so hopefully not an issue.

 

Not sure trying to hold the builder back will work.  I get the impression that once he gets going he's full speed ahead - which is another reason why I'm doing a bit of homework now.

Less haste = more speed, and then no expensive fixes  

[Gibdog]

Hi @Bancroft, I posted a similar (but much less through) Q just before Christmas and someone pointed me to this thread.  Have you finalised the penetrations?  Would you be up for sharing it? I'm at a similar stage and my list feels very small (9!).

Many thanks,

Gracie

[Alan Ambrose]

>>> Is it worth considering just a single electrical supply out and then putting another meter box in the garage to split all the external requirements from there? 

 

As it’s usually much easier to do lines into a garage, yes reckon so, also for ethernet (with a separate POE hub there). In fact, I could see 2 or 3 consumer units - in another thread, someone suggested a separate CU for the kitchen rather than running everything back to the main CU. Seems helpful.
 

[Bancroft]

On 25/11/2024 at 14:37, Russell griffiths said:

cat 6 out to electric gates

For some reason I read this as '6 cats out to electric gate'.  Was about to call the RSPCA!

[Bancroft]

On 02/01/2025 at 14:26, Gibdog said:

Have you finalised the penetrations?  Would you be up for sharing it?

Hi Gracie,  not completed yet; architect working on it still.

 

But what I have so far is as shown here.

[Gibdog]

Thank you - that's a lot bigger than my list! I'll check again.

 

May I ask what the solar conduit is? Are your panels not on the roof..?

 

And your broadband - is that with Virgin by any chance? Are you using the same duct as electrical cable..?

 

Many thanks.

[Nickfromwales]

@Gibdog

The extra penetration for sewage and grey water vs one duct for both will depend on whether you have a sewerage treatment plant or not  If you're on a network sewer then no need to segregate them.

 

You shouldn't really have any 'sensitive' or low voltage services in with mains cables tbh, I'm sure it's been done under duress a thousand times though, but this is a new build / new design so best to do things right. GTC (I worked with them in Gravenhill in oxford) would point blank refuse you a connection if you asked them to pull the same 2 cables into the one duct, so beware of getting refusals to connect / adopt your chosen methodology with groundworks from 3rd party providers! BT will want you to use a specific (BT56) rigid duct which they usually supply you FOC.

 

If you search on here there are threads showing the recommended separation of incoming underground services when sharing the same trench etc  which will help with economising on the number of trenches etc.

 

Remember there are different size ducts, so some will be small 50mm ones, medium are ~75mm and bigger ones are 100-110mm (or larger), so don't install a bigger duct than needed for say the incoming internet provider (50mm is ample there). Cold mains will need the bigger size because of the minimum bending radius of 32mm MDPE, same for the incoming mains steel wire armoured cable, and so on.

 

If you don't need a sprinkler / automatic fire suppression, then the outside taps should all come off the incoming cold mains MDPE (blue alkathene) pipe and (ideally) not after the domestic stopcock in the house, thus saving another penetration. The house water pressure can be more adversely affected by the outside taps coming after the internal house stopcock, and I avoid this whenever I can by simply T'ing off the incoming 32mm pipe with feeds to various outside tap locations, underground.