The waterproof membrane is the most important element in fulfilling a roof’s primary function - keeping the building dry. However, driven by the need to cut energy consumption and emissions, Building Regulations now require roofs to be multi-functional. The first step in creating such a roof is to consider the main waterproofing types. This will help identify the properties required of the other roof layers and so create the correct specification.

There are three main types of flat roof:

Warm Roofs
(the insulation is laid above the deck along with a suitable vapour control layer (e.g. polythene or a metal-core bitumen felt).

Cold Roofs
(insulation is laid beneath the roof deck with a ventilated void).

Inverted
(insulation is laid above the membrane).

For warm roofs the issue of membrane attachment is critical. The membrane must either be secured to the roof structure using sufficient mechanical fixings to resist the wind load forces, or adequately fixed to the roof deck along with all the preceding layers. This makes the attachment of the vapour control layer critical. It also requires the insulation boards to be compatible with the adhesive methods, capable of creating a suitably strong bond and able to provide the necessary safety factors.