INVERTED ROOF SYSTEM

Insulation can be incorporated into a flat roof construction either over or under the waterproof membrane of the roof. Where the insulation system is placed on top of the waterproof membrane this is usually referred to as an inverted roof system. Such an inverted roof system protects the waterproof membrane from thermal shock, the affects of sunlight and weathering, and damage by roof traffic. An inverted roof comprises a weatherproof membrane covered by rectangular, foamed polystyrene insulation boards (30) arranged in a herringbone pattern. Each of the insulation boards (30) has a ratio of long to short side of 2:1 with tongues (31) formed on an adjacent long and short side and corresponding grooves (32) formed on the other two sides. A permeable membrane (35,36) having a weight of between 3 and 15 kilograms per square meter and preferably between 4 and 7 kilograms per square meter covers the insulation boards (30).