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.

Vapour control layer cold flat roof.

A vapour control layer helps you shield your building from the consequences of condensation. 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. An effective vapour control layer at ceiling level an unobstructed 50mm ventilation space above the insulation.

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