Vapour Control Layer Cold Flat Roof

A vapour control layer or vcl on a warm flat roof sits between the roof decking and the insulation.

Vapour control layer cold flat roof.

It has transpired that there is no vapour control layer fitted. Condensation is generated when warm moist air rises and condenses into a liquid on contact with the cooler areas above the insulation. Because of this the vcl always sits at the warm side of the insulation. An effective vapour control layer at ceiling level an unobstructed 50mm ventilation space above the insulation.

Be it a cold or warm roof construction the primary function of a vcl is to keep warm moist air from inside the building inside the building. The roof is an unventilated warm roof design finished with a single ply membrane. Cold flat roofs are difficult to detail correctly but where used they should be in accordance with bs 5250 and have. A vapour control layer helps you shield your building from the consequences of condensation.

The notion behind a vapour control layer is to install it on the room side of the insulation so it stops the passage of warm moist air entering the structure. It s the first line of defence against high vapour pressure air entering the roof structure and causing interstitial condensation.