I am renovating a barn which has vaulted ceilings. The purlins are exposed but the rafters will be covered in plasterboard. After the insulation has been placed between the rafters there is a small space on the rafter between the lower edge of the rafter and the insulation of about 1.5cm where lighting cable can be run - is this permisible. It will not be enclosed in any conduit or trunking. It would be very close under the plasterboard but this will be screwed to the joists.