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Routing cables when insulated plasterboard direct fix to walls

Discussion in 'Electrics UK' started by Kaymo, 11 Nov 2019.

  1. Kaymo

    Kaymo

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    Hi,
    I've gutted a room down to brick and I am soon to start putting it back together. Space is at a premium so I planned to bond insulation direct to the wall and plasterboard direct to the insulation, but before I do that I wanted to think ahead about how the electrical cables will be routed around the room.

    For the lighting, the incoming cable is more or less where it needs to be at ceiling level, but will need to come down maybe 30-40cm to where the wall lights will be. The mains wiring enters at ground level to one side of the room and would need to go up to where the sockets will be.

    My question is whether it is acceptable to chase into the insulation for those short runs, then put the plasterboard over the top?

    In terms of getting the mains cable around the room, I noticed that some skirting board companies offer the option of a cable channel at the back of the skirting. I presume that as these are commonly sold they are ok, but maybe I shouldn't presume!?

    Thanks in advance.
     
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  3. Simon35

    Simon35

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    Dot and dab insulated plasterboard directly to the brickwork, the cables sit against the brickwork in the right void between insulation and wall.
     
  4. jonbey

    jonbey

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    that wont create a vapour barrier, which is often needed to stop condensation problems.
     
  5. Kaymo

    Kaymo

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    Thanks Simon. I had planned to use adhesive foam rather than dot and dab, but I can see what you mean. I had presumed that it wouldn't be acceptable for the cable to be buried under the insulation though, in case it overheats.


    I think the vapour barrier is usually on the warm side of the insulation anyway.
     
  6. SFK

    SFK

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    Kaymo
    Not sure if you are using PIR and then bare plasterboard ontop, or insulated plasterboard. I was using PIR on wall and then bare plasterboard on top.

    As my PIR was entirely flat against the bricks and so no free space, and I wanted no breaks in the vapour barrier, in my 2.5cm deep PIR board, once I had put the PIR board up, I cut 1cm deep by 3cm wide channels in the now front face of the PIR board to take the wires.
    These channels were always in the safe zones, ie from ceiling straight down to light switch, left to right circling the room for the sockets.

    This way the cable is not fully surrounded by insulation.

    I lined this Chanel with Aluminum tape (the same as used to cover the joins in the boards) to keep the vapour barrier in place.

    SFK
     
    Last edited: 12 Nov 2019
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  7. Simon35

    Simon35

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    It's better to have the cable against the brickwork, rather than chased into the insulation.
     
  8. Simon35

    Simon35

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    Insulated plaster board comes with a vapour barrier between insulation and plasterboard, on the warm side of the insulation.
     
  9. jonbey

    jonbey

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    Didn't know that. Cheers
     
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  11. jonbey

    jonbey

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    This is what I did too. My electric cables are under the suspended wooden floor and go up to sockets, so shorter run, and light switches were all on inside walls. But only last night I mad a little channel for some cable in the bathroom install (maybe I will widen them). Probably a pic of what I did before somewhere too ...

    not the best photo, but I guess not so easy in the bonded insulated plasterboard?

    IMG_20180822_154537466_HDR.jpg
     
  12. Kaymo

    Kaymo

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    Thanks SFK, this sounds exactly the same as I was trying to describe (badly) in my OP, but reassuring to hear someone else has done same. Good tip on lining with the foil tape also.
     
  13. Kaymo

    Kaymo

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    Think I am sorted now for the short runs in the safe zones to the lights and sockets, but looking at diagrams of the safe zones online, cables behind the skirting board wouldn't seem to comply. I wonder, if cables are in a specially designed channel in skirting board, does that then count as surface mounted conduit?

    Not sure how I would get the cables around the room otherwise, unless I chased into the surface of the insulation just below the ceiling, which if the diagrams I am looking at online are up to date, would appear to be considered a safe zone.
     
  14. SFK

    SFK

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    Kaymo,
    Pleasure.
    The photo Jonbey used is exactly the same as how I did it.
    Although I sometimes used dry liner boxes.

    I also put the the boxes in after putting up plasterboard.
    So I put in the cables , marked on the floor where they where and how high. Then I put up the plasterboard and cut hole in the plasterboard (very carefully as there are now cables behind) for the metal or dry lining box. Cut bigger hole in insulation to take box. Put box into hole pulling cables into box (remembering to rubber O ring into metal box to stop cable being damaged).

    SFK
     
  15. SFK

    SFK

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    Kaymp,
    Sorry regarding safe zones at coveing height, I do not know as I was able to go into ceiling.
    Note that I minimized this as my cable went all round the at socket height, helped by me having two sockets on each wall. Only place it went into ceiling was as it went over the door.
    SFK
     
  16. Simon35

    Simon35

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    Genuine question, what's the gain in chasing cables into the insulation and using separate insulation and plasterboard? Is it for airtightness?
     
  17. SFK

    SFK

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    Simon,
    In my case it was POSITIVES 1) cost and 2) air tightness 3) Space
    NEGATIVES: 1) Slower

    1) Drafts were a big issue for my room, so by putting up PIR first I was able to seal every crack with spray foam and Aluminum tape. I was also able to double thickness cold (north) walls.

    3) As room is small, I wanted every mm, and so my PIR is flat against wall with no d&D thickness, no cable space, and no dead air space.

    2) And for me it worked out cheaper as it was not an even size room, and lower than 240cm. So on the last wall I was able to use all the PIR offcuts taped together, and then covered with one big sheet of Plasterboard.
    With insulated plasterboard I would have been throwing away lots of the tops of (expensive) insulated plasterboards.

    The negative side was that it was a slower process than if I had used Insulated boards.
    SFK
     
    Last edited: 12 Nov 2019
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