The Cold Deck is the most common but also the least thermally efficient design of roof insulation. … In a cold deck design it is very important to have good air flow that will allow warm moist air to escape. Condensation can lead to rotting deck and ceiling joists and also cause damp insulation and ceilings.
A warm roof is a type of roof construction which has an insulation layer above the rafters, and immediately below its weatherproof membrane… A warm roof construction allows heat to be conserved within a property – without the need for a ventilation system.
A vapour control layer helps you protect your building from the consequences of condensation. Condensation is formed when warm moist air rises and condenses into a liquid on contact with the colder surfaces above the insulation
Vapour control layers are always required whenever you insulate, irrespective of the insulation used. They should be used to form a continuous airtight layer and so all the joints and any penetrations must always be sealed with the appropriate airtightness products.
In a warm roof construction the principal insulation layer is placed above the structural decking, resulting in the structural deck and support structure being at a temperature similar to that of the building interior. … The waterproofing system is placed over the insulation to completely encapsulate it.