Vapour Control Layer Cold Flat Roof

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.

Vapour control layer cold flat roof. The architect plans stated requirement for a vapour control layer below the insulation or a 3 in 1 insulation board including vapour control layer and an additional foil backed plasterboard. A vapour control layer helps you shield your building from the consequences of condensation. Because of this the vcl always sits at the warm side of the insulation. It has transpired that there is no vapour control layer fitted.

The roof is an unventilated warm roof design finished with a single ply membrane. It s the first line of defence against high vapour pressure air entering the roof structure and causing interstitial condensation. Cold flat roofs are difficult to detail correctly but where used they should be in accordance with bs 5250 and have. 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.

Breather membranes are positioned to the outside of the insulation acting as a weather barrier while still allowing moisture particles to escape from the inside. A vapour control layer or vcl on a warm flat roof sits between the roof decking and the insulation.