As stated in US patent 2003 building membranes or architectural fabrics are a part of the building structure. They protect people from weather elements such as wind, sun, rain. They can be a permanent part of the structure or temporary. They should be water resistant, fire resistant, resistant to UV radiation and have an attractive appearance.
Membranes are divided by type on vapor barrier and wind – waterproof (or breathable, vapor permeable) ones, and by use in building structures – on facade ones, in heat insulation system of mounted ventilated facade (MVF), and the underlay ones – in the «roof pie» system.
The main function of the membrane is protection of the mineral wool insulation from wind, moisture and condensation, and also the emission of fibers from the insulation. The greatest effect of membrane properties is achieved in extreme conditions – long winters with high humidity and strong winds.
An additional important property of membranes – protection of mineral wool insulation from moisture caused by rain during installation and from solar ultraviolet during the long break, before covering by a mounted facade. It is known that UV radiation quickly destroys silicone water repellent and a synthetic binder of insulation fiber.
Mineral wool has two major advantages: it does not burn and pass steam perfectly. And the main disadvantage – unlimited breathability.
It is known that still air is the best heat insulator after vacuum, if it is in closed insulation cells. Such insulation materials are polystyrene foam and polyurethane foam, which in turn burn well and do not have the necessary vapor permeability.
But what if the air is walking freely in the heat insulation? Wet and warm air comes from inside of the building through the wall to cotton insulation (exfiltration) and from the outside a frosty wind blows on the cotton insulation through the ventilation gaps of the facade (infiltration). Opposing eddy currents meet each other in the insulation where moisture condenses and becomes water.
It is known that during winter the heat insulation, even protected from the wind by a layer of vapor permeable plaster, gaining up to two kilograms of water per square meter of wall area. Obviously, in that case you can forget about the heat insulation in winter.
Calculations show that without windproof membrane insulating properties of the heat insulation is reduced in four times.
Under cyclic freeze-thaw process we can observe the aging of the binder over time. There may be potential manufacturing defects in any material, weak points in the insulation develops a catastrophic process of increasing destruction. Weak points are accumulated, their number increases, their areas are expanded. And now the walls are frozen, there is mold, fungus, allergens airborne droplets spread on the premises, and people get sick, they do not know why.
But if you just cover the insulation on the frosty street side by a windproof “breathable” vapour permeable membrane, the infiltration stops, the warm zone in the insulation will instantly be protected from external cold, the steam will be released freely from the insulation and will condense in the outside air.
In addition, along the fiber surface of the wool the air moves in turbulent flow, and along the film (membrane) – laminar flow.
If the membrane increases the stillness of the air in the insulation, then question of the quality and properties of wool as a heat insulator will lose its relevance.
For these reasons it is highly recommended to use windproof membranes with cotton insulation.