Cold Roof Vapour Control Layer

Don t get caught out by ignoring the vapour control layer.

Cold roof vapour control layer.

A vapour control layer or vcl on a warm flat roof sits between the roof decking and the insulation. It has transpired that there is no vapour control layer fitted. Access hatches to cold roof voids should have. The notion behind a vapour control layer is to install it on the room.

Bs6229 2003 gives advice on vapour control layers in flat roofs and the control of condensation within the building generally. Vapour control layers should be provided to warm roofs and. Where the ceiling below a cold pitched roof includes a vapour control layer the design should ensure adequate ventilation is provided to the habitable areas to prevent condensation problems in the home. We would recommend either a fully warm roof with insulation on top of the roof deck or a cold roof with a minimum 50mm well ventilated cavity between the roof deck and the top of the insulation.

It s the first line of defence against high vapour pressure air entering the roof structure and causing interstitial condensation. 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 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. Include at least one layer of bitumen roofing membrane s2p3 below the insulation fully bonded or mechanically fixed to the structural deck as appropriate or a suitable self adhesive or torch on membrane.

Because the waterproofing layer constitutes a vapour control layer on the cold side of the insulation there is a high risk of harmful interstitial and surface condensation on the underside of the deck or the upper surface of the. Meets building requirements non ventilated pitched roof systems that use tyvek as roofing underlay satisfy the requirement of approved document c2. The roof is an unventilated warm roof design finished with a single ply membrane. To solve this we recommend installing an air vapour control layer avcl such as duponttm airguard control beneath the vapour open quilt insulation.

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.