On a new build garden studio, the flat cold roof has insulation between the joists > VCL > 25mm services void > plasterboard. I think I would like to beef up the insulation by adding an extra 25mm of rigid insulation into the services void. The ceiling wiring (mixture of 1mm and 2.5mm T&E - RCD protected circuits) is fixed to the underside of the joists and won't be covered by the insulation. I presume I need to leave a gap between the insulation boards and the cables, is it sufficient to just ensure the cables are not touching the insulation or do I need a larger 'air' gap?
