Re-wire idea - advice sought

[charlie30]

Hi everyone, I would appreciate any comments you have on this re-wire suggestion.

The property is an ex-LA one with concrete floors and solid walls, the current electrics are run throughout the property in purpose built plastic skirting which also houses sockets, this skirting is being removed as it is in disrepair.

Our original plan was for new wiring to be run high up on the ceiling, which would then be covered with a new plasterboard ceiling. The wiring would then drop down the walls via chases. We now realise the current ceiling and walls are in good shape and are reluctant to do this.

As an alternative, we are considering raising the floor instead, with a layer of 15mm high density insulation board (to help with acoustic and heat insulation), on top of this would be 20mm thick wood board (the sort used say under tiling).

My re-wire suggestion is to simply run wiring in the 15mm insulation board layer, via dedicated groove cut-outs. The 20mm thick wood board layer will then cover it all.

Please advise on any obvious problems here? Any one have experience with similar situation?
I have an electrician for my electric work but would really appreciate the forum's input too, cheers.

 

[Chri5]

Is it a house or flat.

Raising the floor by just 15mm and then having a 20mm board has some hazards.

How would the board be fixed, wouldn't the fixings end up (potentially) go through the cables underneath ?

What about the derating factors for cables running in insulation, and likely for grouping ?

What would you put on top of the floor boards, a nail down flooring system might also damage cables. How would you do the lighting cabling element of the rewire ?

 

[ban-all-sheds]

How would the board be fixed, wouldn't the fixings end up (potentially) go through the cables underneath ?

And even if they don't other fixings might at a later date.

522.6.5

 

[charlie30]

Cheers for the quick responses.

The property is a flat, on the 1st floor of a 3 storey building.

On top of the concrete floor will sit 15mm of rigid high density insulation board, and channels will be cut out of this to lay wiring. This board will be glued down using something like Grip fill, and is as rigid as wood.

On top of this will be a layer of standard floor board, 20mm I think. I had planned to bed this in using a cement based adhesive, which will allow some degree of floor levelling too.

All layers are rigid so no chance of movement, the floor board will barely 'flex' when in place.

On top of this will be laminate flooring, tiling, or carpet. Any nails going through the floor may disturb the wiring, would you recommed additional protection to the wiring?

I'm unsure of the derating factor stuff, can you describe this a bit?

Thanks again everyone, the more I think about it the better this solution is. It does mean having to replace the doors and door frames, but there are only 4 doors to do this to! Which is a lot less work than say a false ceiling throughout with wall chasing.

 

[charlie30]

My main concern was the permitted areas of wiring, which I understand is horizontal/vertical to sockets/switches, and within 15cm (I am not 100% sure) area of where ceilings and walls meet.

Little is written about floors... although I guess my situation is not too different from say a house with standard floor boards that can be lifted.

 

[ban-all-sheds]

Any nails going through the floor may disturb the wiring,

"Disturb"?

I have an electrician for my electric work.

would you recommed additional protection to the wiring?

Yes, but it's not what we recommend, it's what your electrician recommends which is all that matters. Are you aware of the law?

I have an electrician for my electric work.

I'm unsure of the derating factor stuff, can you describe this a bit?

Don't worry, your electrician will be sure of it.

I have an electrician for my electric work.

Little is written about floors...

There are things written about them in the wiring regulations, but don't worry, your electrician will know.

although I guess my situation is not too different from say a house with standard floor boards that can be lifted.

522.6.5

But don't worry, your electrician will know what that says.

It does mean having to replace the doors and door frames, but there are only 4 doors to do this to!

Don't do anything related to that until your electrician has told you how much you'll have to raise them.

 

[charlie30]

Hi ban all sheds, yes am aware of the law, all work is being done by my electrician.

I even go so far as not to allow my electrician to cut the seal on the my electric meter. I actually went through all the hassle to get EDF to come and disconnect and reconnect on a later date to allow electrician to replace consumer unit (he also fitted a Wylex isolator, so I never need to call EDF again).

 

[ban-all-sheds]

Hi ban all sheds, yes am aware of the law, all work is being done by my electrician.

Then as you are aware, you may not decide where the cables will run, you may not decide what size the cables will be, you may not decide what protection they need and you may not decide how thick the floor shall be.

 

[charlie30]

Ban all sheds, I appreciate I cannot make these decisions, nor can you on my electricians behalf. But what about a general discussion on my concept? We are not all cow boy electricians on here you know!

 

[ban-all-sheds]

Your floor will end up at least 65mm thick, and your cables will all need to be much thicker than normal - I think your concept is deeply flawed.

 

[flameport]

Cables in the floor won't achieve much - how are the cables getting from the floor to the sockets on the walls?
How is the lighting going to be done? No use putting lighting cables in the floor.
To avoid inevitable damage from nails etc., they should be in steel conduit. However if doing that, why not just put steel conduit around the base of the walls and fit extra thick skirting to cover it? No need to refit doors then.

It is likely that the plastic skirting with sockets in it was used for a very good reason - the walls will be a solid concrete slab which you won't be able to cut into.

The usual options for concrete box properties are:
1. If steel conduits were fitted when the place was built, pull new wires through and keep the sockets in the same positions, possibly adding extras (singles to doubles, etc).
2. If the walls can be chased, run cables at ceiling level and fit coving to cover them. Vertical chases down to the sockets.
3. If the walls are solid concrete, surface fix the new wiring and line the whole place with plasterboard (preferably the type with insulation on the back).
4. Concrete ceilings without conduits only have one option - line with plasterboard.

 

[mikhailfaradayski]

And just to add another thought to your floored/flawed idea.

You better make sure that you have planned every last detail before you, oops, i mean your electrician does anything.

Can you imagine the grief involved in adding just 1 more cable after the everything has been laid, carpet et al?

You should ask your electrician for his thoughts.

 

[charlie30]

Just to clarify, the wiring I'm suggesting to be put into the floor is just for the bedroom and living room wall sockets.

A 65mm floor is not a problem, I doubt it will be that thick unless there is a requirement for wiring to be a certain distance below the surfance. However I have such noisy neighbours downstairs that I could do with all the sound insulation I can get!

It is a local authority building (and the flat I have I bought the lease many years ago) and I have seen how the council's appointed electricians have recently re-wired some properties, surface trunking in many places.

I also think my idea is cheaper than getting my builder to chase walls and build a false ceiling....

(BTW Chri5 - the lighting circuits are fine as they are, and would not be involved in the floor.)

 

[mikhailfaradayski]

... the more I think about it the better this solution is....

Thats a bit like F***ing a Porcupine

 

[ban-all-sheds]

A 65mm floor is not a problem, I doubt it will be that thick unless there is a requirement for wiring to be a certain distance below the surfance.

50mm.

I have seen how the council's appointed electricians have recently re-wired some properties, surface trunking in many places.

There's a reason for that.

I also think my idea is cheaper than getting my builder to chase walls and build a false ceiling....

You made your mind up to do this before you asked here, didn't you...