Bitumen is one of the best waterproofing mediums which has been used for ages. However one issue with bitumen is its brittleness leading to cracks during daily expansion and contraction of the modern RCC roofs, in absence of good thermal barriers. Hence for this waterproofing system, it is recommended that an insulation layer is provided to prevent differential heat from reaching the roof slab. This will ensure that the underlying bituminous waterproofing layer does not crack. However one should ensure that the bituminous coating is compatible with the polystyrene in the insulation, as volatiles in the bitumen have a tendency to dissolve polystyrene.