Light Fixtures within Insulated Flat Roof

[watsite]

Hi All,

I am currently renovating a master bedroom which is part of an extension with a flat roof. I have had to take the ceiling down so some structural work could be completed and am taking the opportunity to insulate with celotex boards with add a vapour barrier.

My question relates to the installation of the exiting light socket/cabling within the roof space. I am aiming to tack the light cabling to the joists within the 50-70mm ventilation gap within the roof space, but am unsure how to proceed from there. Do I need to clear the insulation/vapour barrier either side to the cable where it penetrates the ceiling or can I just cut a whole in both and feed it through. I am not planning to use recessed lights (as from what I read they are not a good idea in flat roofs); I want to install a track light.

 

[skenk]

If the cable just needs to pass vertically through 70mm of insulation and you use 1.5mm t&e on a 6A mcb it will be fine (no need to clear insulation away).

 

[watsite]

Thanks skenk, the insulation debth is likely to be 140 mm, would this cause any issues i.e would the cable be derated etc?

 

[skenk]

Not as long as you use 1.5mm cable and it's on a 6A mcb