In general, the water vapour pressure inside the house is greater than the vapour pressure outside. As well as heat trying to escape the building, so too water vapour tries to escape through the building fabric to the outside. The main mechanism by which water vapour is eliminated should be through adequate ventilation. However, vapour will also try to diffuse through the walls and roof.

Water vapour coming into contact with a cold surface will condense, as can be seen on the inside of windows after a cold night. Condensation within the structure of the roof, known as interstitial condensation, can have adverse effects. Excess water can lead to mould growth, or staining of interior plaster or timbers. To prevent interstitial condensation, the roof structure must be built such that materials with higher vapour resistance are positioned to the inside of the building. This prevents water vapour from penetrating the wall structure to a cold part of the roof. TLX Silver is a vapour barrier, and has a very high vapour resistance. When it is located on the inside of the roof it prevents water vapour from getting into the roof structure, eliminating the risk of interstitial condensation.

TLX Silver standard solutions contain an analysis of the risk of interstitial condensation, calculated to BS EN ISO 13788, which show no risk of harmful condensation. The calculation assesses diffusion of water vapour through the materials of construction, but not water vapour in moist air that leaks into the roof structure. It is essential that the ceiling is as well sealed as possible to prevent movement of moist air from carrying water vapour into the roof.

TLX Silver can be used in Conservatory Roof Insulation, new build, barn conversion and refurbishment projects including loft extensions (new build in a traditional roof) either over or under rafters. It works in combination with glass wool to reduce the total thickness of insulation needed and with rigid insulation to cut installation time. BBA approved, TLX Silver saves time and guarantees a u-value of 0.17. It stops air leakage by providing an air-tight vapour barrier and restricting air movement in its multi-foil layers.