Vapour Barrier For Cold Flat Roof

I am building a cold flat roof on an extension.

Vapour barrier for cold flat roof.

Cold roof areas usually include vapour open fibrous insulation e g mineral wool quilt. Which ventilation solutions are available. Room in the roof constructions often use a combination of warm and cold roof constructions with varying types of insulation. When the temperature of the vapour falls to or below its dew point the water vapour condenses on cold surfaces.

Bituminous vapour retarders asphalt mixed with felt or fiberglass or non bituminous vapour retarders plastic. Flat roof vapour barrier materials when constructing a flat roof there are two types of materials commonly used. Most diagrams on the internet i have seen have plasterboard on joist insulation air gap osb board then roofing material. 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.

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. In general the installation of a cold roof is not recommended for the construction of new properties. Why is it the best vapour barrier for flat roofs.

The sloping ceiling areas include closed cell or foil backed rigid board insulants most of which are highly vapour resistant. Temporarily waterproofs the roof can stay uncovered for up to 3 months. A flat roof vapour barrier such as iko s mvp modified vapour protector offers appropriate moisture protection. Any advice would be great.

Vapour resistance of 2000 mns g. The notion behind a vapour control layer is to install it on the room. Do i need a vapour barrier between the plasterboard and the bottom of the joist. Self healing if punctured by fixings.

A vapour control layer or vcl on a warm flat roof sits between the roof decking and the 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.