Concealed membrane

Abstract

Bitumen has traditionally been used as a waterproof layer, applied while hot in liquid form onto a concrete roof slab. As it cools it hardens, forming an impervious membrane, but will soften again if heated by the effects of solar radiation. For this reason, in order to keep the material cool, bitumen membranes are concealed by smooth pebbles, paving slabs, usually with thermal insulation set between the bitumen and the pebbles/paving. Traditional bitumen roofs are usually laid in two layers, with an overall thickness of around 25mm. One of the limiting factors with bitumen is folding the material through an angle. When the material turns through a right angle from the horizontal roof to a vertical parapet wall, it can pass through a maximum of 45° in a single fold. For this reason 45°angle fillets are used to make a 90° turn from roof to wall.