All electrical cable and Cat cabe underfloor in insulation???

[gc100]

Hi,

 

My builders and electrician have decided that given my house design/restrictions the most effective and easy way to perform 95% of the wiring is to put it in the insulation under the UFH and screed. They basically are talking about putting down 50mm over the slab, then the cables in a channel 50mm high and then lay another 50mm insulation above. Then the UFH pipes, then screed.

 

I'm concerned about a couple of main points:

• Excess heating (due to insulation) and then risk of melting/short-circuit/fire
• Not ever being able to access it again

 

What are you thoughts? Anyone done this?

Thanks

 

 

 

[Jeremy Harris]

Put cable ducts in and then just derate the cable to allow for it being within insulation in a duct.  Not hard to pull cables through reasonably sized ducts, and if a pull through rope is left in the duct it's easy enough to add new cables in the future.  Make the cable ducts as large as you can reasonably fit. 

 

We have the cable that supplies our kitchen island running through a bit of duct set into the floor, under our UFH pipes.  I just made sure the bends were nice and gentle at the ends, so that a bit of cable could be pulled through easily later.

[gc100]

Thanks Jeremy. There was talk to using drainage pipe(s) (at least by the builder). Would you recommend individual ducts per wire or something else?

[ProDave]

Why do you need many cables in the floor?

 

The only cables in the floor (or in my case of a suspended floor, well and truly underneath the floor in conduit) is the cables to the kitchen island.

 

I suggest you first re design the cable routes to go around the walls or up the walls to the ceiling / floor void above.

[Jeremy Harris]

15 minutes ago, gc100 said:

Thanks Jeremy. There was talk to using drainage pipe(s) (at least by the builder). Would you recommend individual ducts per wire or something else?

 

 

Use proper cable duct, as it's not expensive, and can be bent to follow gentle curves very easily.  However, as @ProDave says, I'd look at why you need to run cables under the floor.  Most of our wiring runs in the ground floor ceiling/first floor void.  Dead easy to do with posijoists.  It all went in after the first floor was down, but before the ceiling was plaster boarded, with cables run up or down walls from there to outlets, switches etc.

[Temp]

Why can't it go in ceilings?

[gc100]

My build is single story vaulted ceilings and we have only a very small void due to increased insulation and hard limits (window openings). We also have a structural stud wall that runs central down the building with only a void on the room side, so no drilling. To get 'over' the central hallway we'd have to run everything over the vaulted ceilings. We have some steel work that is in the way in runs and will be very tight bottlenecks for the wiring. To compound this we also have the MVHR ducts in the same very limit space. It due to the unusual design on the house imposed by planning restrictions and solution dreamed up by structural engineer.

 

It really is more easy by some margin to run 90% of cables in the foor.

[Russell griffiths]

I have a very similar build, vaulted ceilings throughout, very few internal walls. 

It was suggested to me to put a couple of sub main consumer units on different sides of the house

so instead of running multiple cables in the duct in the floor

run heavier cables to different points of the house to supply the sub boards, then from there run your standard cabling. 

 

We have found a different way of doing it but it but it might help you. 

[gc100]

2 minutes ago, Russell griffiths said:

I have a very similar build, vaulted ceilings throughout, very few internal walls. 

It was suggested to me to put a couple of sub main consumer units on different sides of the house

so instead of running multiple cables in the duct in the floor

run heavier cables to different points of the house to supply the sub boards, then from there run your standard cabling. 

 

We have found a different way of doing it but it but it might help you. 

 

Thanks. Its a good idea. I'm just so limited for space really, I'd have to sacrifice room space which is not ideal.

[ProDave]

Don't forget you can run cables around a wall horizontally from socket to socket or light switch to light switch in safe zones.  Some electricians and a LOT of builders don't realise that is allowed.  (the one time I had a stand up finger wagging argument with a joiner who was trying to stop me doing that)