How to treat under floor electrics with underfloor heating?

[GordonCheeseman]

HI Folks. Forum noob, but seasoned DIYer here.

I'm about to start planning to install water based underfloor heating in an old property with a suspended floor, where the ring main is run under the floor between the rooms.

I know we'll need to remove the suspended floor, level the sub-floor, install insulation and a screed over the water pipes, but are there any specific regs about how the sockets or any ethernet cables should be run?

I'm tempted to put cable runs behind the skirting for future proofing, but wonder what others have done?

I appreciate that this is an electrics question in the plumbing forum, but I thought there may be more experience on the use case in here.

Cheers.

 

[muggles]

No, cables should not be run behind skirtings.

 

[GordonCheeseman]

Ok, so behind the skirting is not an option then.

Has anyone dealt with this problem before and now had to rewire the ring to come down from the room above?

 

[Harry Bloomfield]

Ok, so behind the skirting is not an option then.

They can pass vertically down behind the skirting, but not run horizontally behind it. If the under floor is to become inaccessible, for any future modifications, and you expect them to be needed, then the only other way is down the wall, from above - exactly as would be necessary, with a solid floor.

 

[GordonCheeseman]

Ok that's what I'd need to do in the future. What about the existing cables which run down below the sub-floor. Do they need to be encased in any way, or just pinned to the perimeter wall below the screed, meaning they would be in contact with the insulation?

I'm ideally wanting to avoid the pain of moving the entire ring up a floor and chasing down the walls.

 

[Murdochcat]

Fwiw you are going to have considerable upheaval installing underfloor heating you really do need to consider rewiring the socket circuit from above.

How old is the property ? Wiring ?

 

[GordonCheeseman]

The wiring is within the last 15ish years, but the property is 1896.

I know the pain to come, but want to know whether rewiring from above is a necessity or not.

I'm going back to brick to insulate the outside walls and maybe some inside depending on the state of the plaster, but want to avoid any extra work like take the floor above up to re-run the downstairs ring. Shielding etc.

 

[Madrab]

Have you looked at alternatives to retrofitting to a concrete thermal mass type UFH? Overlay type, Inset etc?

 

[flameport]

I know we'll need to remove the suspended floor, level the sub-floor, install insulation and a screed over the water pipes,

If doing all of that, then it's also time to rewire any circuits which have cables under the existing floor. Leaving any old cables under there and expecting to continue using them would be insane.
It's also the ideal time to consider where and how many socket outlets are actually required, which is likely to be a lot more than it has now.

Option 1 - cables under the floor but installed in conduit so they can be replaced in the future without removing the floor. 20mm or 25mm round conduit would be usual, either steel or plastic, with single insulated wiring pulled through after the floor is installed.

Option 2 - locate cables elsewhere. That could be in the ceiling with drops to each outlet, or more likely would be horizontally between the outlets which will use less cable. Suggest those are also in conduit so that future replacements can be done without destroying the walls.

 

[Harry Bloomfield]

Option 1 - cables under the floor but installed in conduit so they can be replaced in the future without removing the floor. 20mm or 25mm round conduit would be usual, either steel or plastic, with single insulated wiring pulled through after the floor is installed.

Limitation would be two bends, formed in the conduit itself, between each accessible point.

 

[trojanhawrs]

Limitation would be two bends, formed in the conduit itself, between each accessible point.

You can put 4 bends in a conduit run. Would probably need all 4 if they're getting screeded in too

 

[flameport]

Two bends is all that's needed - conduit down from the socket box, 1 bend, across the floor, and another bend up into the next socket.
Repeat for the rest.

 

[Harry Bloomfield]

You can put 4 bends in a conduit run. Would probably need all 4 if they're getting screeded in too

Of course you can, but then try pulling cables through them.

 

[trojanhawrs]

Of course you can, but then try pulling cables through them.

That's why they have fill tables.

Two bends is all that's needed - conduit down from the socket box, 1 bend, across the floor, and another bend up into the next socket.
Repeat for the rest.

Suppose that depends on how they're going about concreting the floor/supporting the existing walls. I was thinking out into the main floor area and back out to the wall

 

[Harry Bloomfield]

That's why they have fill tables.

The fill tables, are just that - the number you can get into the conduit, they take no account of being able to actually pull cables in. Even supposing you could pull them in, what if the draw-wire snapped? Chances of pushing a new draw wire in through four bends - near zero..