Vapour Control Layer Cold Flat Roof

It has transpired that there is no vapour control layer fitted.

Vapour control layer cold flat roof.

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 helps you shield your building from the consequences of condensation. Condensation is generated when warm moist air rises and condenses into a liquid on contact with the cooler areas above the insulation. A vapour control layer or vcl on a warm flat roof sits between the roof decking and the insulation.

Cold flat roofs are difficult to detail correctly but where used they should be in accordance with bs 5250 and have. Because of this the vcl always sits at the warm side of the insulation. 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. 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.

Vapour control layers are positioned to the inside of the insulation in order to minimise the amount of warm moist air entering the construction. The roof is an unventilated warm roof design finished with a single ply membrane.