The Inverted Roof Principle

Unlike the conventional warm roof, on the inverted roof the roof waterproofing membrane is located directly on the concrete deck - beneath the XPS thermal insulation. On top of the thermal insulation, a vapour-permeable but not waterproof separating layer or fleece drains a large proportion of the accumulated rainwater. The residual water penetrating through the separating layer is channelled away by the water-repellent insulation layer and its joints and drained via appropriate roof drains at the waterproofing membrane level. 

1 Structural deck
2 Roof waterproofing membrane, two-layer
3 Water-resistant insulation layer
4 Filter and protective layer
5 Gravel layer