I have 100mm of insulation between rafters as per drawing. Now I need Kooltherm K18 to the underside of the rafters but the drawing doesn't say what thickness to use?
It says next I will need 12mm thk foil backed plasterboard, skimmed. I don't understand. Why do I need that as well? As far as I know the K18 = an insulation and 12.5mm plasterboard itself. How thick should be the insulation layer then in my case if I already have 100mm?
It says next I will need 12mm thk foil backed plasterboard, skimmed. I don't understand. Why do I need that as well? As far as I know the K18 = an insulation and 12.5mm plasterboard itself. How thick should be the insulation layer then in my case if I already have 100mm?