Lighting wiring in a extension with flat roof

[damnar]

Hi,

Am looking at installing lighting wiring in a single story extension with a flat roof. Construction is 175mm depth timber joists with 100mm celotex between starting at lower edge of joists, battens fixed over this, with plywood covering and bitumen roofing felt to top out. 25mm celotex then fixed below joists, with 12mm plasterboard to hold it in place.

My question really is: can I run wiring in void above joists (quickest and easiest route) bearing in mind its heated by the sun from roof above. Anyone got any experience of how hot it's likely to get up in there?
Can possibly use 90 degree cable instead of standard T&E.

Any ideas? Many thanks.

 

[SirKit Breaker]

Cant see a problem with what you propose as long as the cables are adequately protected from being trapped, damaged or whatever.
The heat shouldnt be a problem, i have done loads of loft conversions and clipped cables to the roof trusses, these are also heated from the sun and usually covered to some degree with kingspan. None of them have burned down yet, but then there is always a first time!

Just make sure you don't overload the cables, use 1.5mm not 1.0mm.

Cheers..howard

 

[damnar]

Good to know. Thanks for the reassurance
Current carrying capacity isn't the main issue in this case. Was a bit worried that temperature might top the 70 degree max for conductors during summer days as roof void is basically a thin sandwich of air between insulation underneath, and black roofing felt on top. Contemplating using 6242b LSZH cable as conductor temp allowed to reach 90 degrees. Other option is to run cables on insulated part of joists as protection from overheating!! All depends on temperature in roof...