Flat
roofs consist of a single ply membrane over Kingspan Thermataper TT47 insulation tapered to achieve a 1:60 fall, over an 18 mm
plywood deck on 219 mm Easijoists forming a services void, with a plasterboard finish.
In typical
roof assemblies, this moisture is driven inwards through vapor permeable roofing papers / felts into
plywood and OSB
roof decks, and subsequently through the other side of the
roof deck into the attic space.