Flat roofing

Cold roof

Insulation located at ceiling level; void or roof slab is insulated from heat loss from below and is therefore at a colder temperature than the room during cold weather. With this form of construction there is a risk of condensation forming within the roof void or on the underside of the slab, so good cross-ventilation is essential. Vapour control layers at ceiling level are essential, but not 100% effective.

Quasi cold roof

Roof constructed as above, but without the insulation layer. Risk of condensation forming either on soffits of slab, interstitially or on reverse face of roof deck, i.e. the cold surface.

Warm roof

Insulation placed on top of the roof deck but beneath the waterproof membrane. Vapour control usually placed under the insulation. This form of roofing has a much reduced risk of condensation as the ceiling or roof void is at a similar temperature to the roof. However, the system prevents heat from infrared radiation from being dissipated.

Inverted roof

A roof in which the insulation is placed on top of the waterproof membrane. No vapour control is needed. Roof void and or deck are maintained at similar temperature to the room. The insulation protects the membrane from damage but must be anchored down. An inverted roof is also a warm roof.