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Wall Cavity Wiring.

Zoomup
Good morning on this bright and sunny start,


                          Q. Which regulation(s) specifically prohibit(s) the installation of cables in brick and block cavity walls within the cavity?


in a, Older premises?


    b, Newer premises?


If regulations exist, what reasons are provided for the prohibition? Or are we just concerned about chemical damage of cable insulation if the cables are in contact with some types thermal insulation?


Z.
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    Sparkingchip:

    So you're lying on a bit of board spread across the top of the ceiling joists having pulled the fibreglass insulation back trying to drop a fishing line down the cavity over the top of the wall plate when you discover the brickies sealed the top of the cavity,  just like they are supposed to.


    Andy 




    Vented cavities were all the rage in the 50s. they usually left the wall uncapped and put air bricks in the wall at low and high level. I was told it was to allow the cavity to breath and therefore dry. But of course for insulation purposes it effectively reduced the wall to a single brick. I was even worse in my own house as there were also air bricks at high level internally. 


    I did an EICR on a TT house. The tails disappeared into the wall by the meter (no upfront RCD and only the suppler fuse) and emerged about 4metres horizontally, having run under the kitchen window,  and 1.5 metre vertically away having run through the cavity. From memory I gave it a 3 with lots of words about the potential risk, should it have been a 2 but as has been said what reg?

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    I suspect an odd length of T and E won't make that much difference, it is scarcely a good wicking material.



    It's not the wicking effect that's the issue, but forming a bridge that's downhill from outside to inside along which drops of water can descend - a nice smooth impermeable surface (like a cable sheath) is far more efficient in that respect than an absorbent material. For sure there are a lot of variables - if you're in a sheltered part of the south east where the local venacular is to have the roof oversailing the walls by a considerable distance so the walls are usually kept dry you're most unlikely to have problems. But around here where the rain comes in off the Pennines horizontally on a good day and roofs typically stop promptly at the top of walls (to stop the edges of the roof being lifted by the wind), it's quite common to have the outer leaf completely saturated. Indeed there was a trend in these parts, going back well into early Victorian times, if not earlier, to build outer walls with a significant air gap in the middle - connected by a few carefully chosen 'through stones' in lieu of wall ties. The text books might still classify them as 'solid walls' as they don't quite meet the standards for a proper cavity wall, but mostly the intention and effect was the same. I can't see builders going to all that effort if they weren't convinced of the benefits.


        - Andy.
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    @zoom - are you getting to the point that you consider there is no Regulation ?   What do building regs say about it though; I'm not totally familiar and perhaps being lemming like, I just followed what I thought I was told, that cables in cavities are a no-no - condensation, snags, insulation (current/future) etc...but nothing in BS7671 is what you are getting at ?
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    Hello Psy, after providing an estimate for installing some new sockets in a 70s bungalow I considered if it was possible to run cables down to the new socket positions from the loft in the wall cavities. This would save a lot of time, dust, noise and disruption. So I enquired about the possibility here to get responses and opinions. I could use PVC/PVC cable or M.I.C.C. if necessary, or any other suitable cable.


    Z.

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