Flat roof – conventional warm roof

Flat roof – conventional warm roof

Most warm flat roof constructions consist of a structural deck with a vapour control layer, thermal insulation layer and waterproofing installed over. It is often described as a ‘conventional’ warm roof because it is a common solution, suitable for projects of all sizes – from small domestic to large commercial or industrial.

The protection afforded to the insulation by the waterproofing layer means a wide range of insulation materials can be used, and the performance characteristics that make extruded polystyrene (XPS) the preferred choice for inverted flat roofs are less significant.

There is a huge range of waterproofing options, from traditional and modern types of built-up felt roofing, through the many polymeric single ply membrane materials and their attachment methods, to liquid-applied systems. All require slightly different things of the insulation board to which they are applied.

Despite being offered almost exclusively for inverted roofing, occasionally XPS boards are specified in warm roof constructions. Usually the intended waterproofing is a single ply membrane, but specifiers should consult with the manufacturers of the insulation and the intended waterproofing for further guidance, as there are significant differences in performance requirements.

For example, the ballast on an inverted roof is usually of a type that is known to resist fire spread. The fire performance of a warm roof depends on the waterproofing and the deck type, so the suitability of a particular combination of materials may depend on the availability of test data.

Polyfoam XPS Ltd is a leading manufacturer of closed cell, extruded polystyrene insulation. The Polyfoam range is lightweight, strong, moisture resistant and easy to cut and shape, providing thermal performance and strength for the lifetime of the building. Recommended Polyfoam XPS products for conventional warm roof applications are: