Vapour Barrier For Cold Flat Roof

Vapour resistance of 2000 mns g.

Vapour barrier for cold flat roof. For cold flat roofs the vapour layer needs to be positioned underneath the insulation layer on top of the room below to create an effective barrier. The notion behind a vapour control layer is to install it on the room. Its not cheap purchasing it by the role and by the pallet load is cheaper but is a considerable layout. Most diagrams on the internet i have seen have plasterboard on joist insulation air gap osb board then roofing material.

Do i need a vapour barrier between the plasterboard and the bottom of the joist. It s the first line of defence against high vapour pressure air entering the roof structure and causing interstitial condensation. Cold roof areas usually include vapour open fibrous insulation e g mineral wool quilt. Which ventilation solutions are available.

In general the installation of a cold roof is not recommended for the construction of new properties. Temporarily waterproofs the roof can stay uncovered for up to 3 months. The sloping ceiling areas include closed cell or foil backed rigid board insulants most of which are highly vapour resistant. Condensation within a flat roof mainly occurs during cold weather when moisture vapour in the air which has been generated within the heated building rises from the room below into the cold roof void above the ceiling.

Bituminous vapour retarders asphalt mixed with felt or fiberglass or non bituminous vapour retarders plastic. When the temperature of the vapour falls to or below its dew point the water vapour condenses on cold surfaces. A vapour control layer or vcl on a warm flat roof sits between the roof decking and the insulation. Room in the roof constructions often use a combination of warm and cold roof constructions with varying types of insulation.

Why is it the best vapour barrier for flat roofs. I am building a cold flat roof on an extension. Because of this the vcl always sits at the warm side of the. Flat roof vapour barrier materials when constructing a flat roof there are two types of materials commonly used.

Self healing if punctured by fixings. Any advice would be great.