THE BUILDING’s SKIN
A well-designed building skin is like a down jacket: there is an outer and an inner layer and in between is the insulation.
Every building needs an outer and an inner skin in order to stay tight and keep wind and weather out and comfort in. The outer layer is known as the wind-tight level and the inner layer as the air-tight level.
The wind-tightness of the wall is achieved by the external rendering or by boards or wind and rain-tight adhesive membranes on ventilated constructions. Façades with open gaps and glass façades are furnished with permanently UV-resistant façade linings.
Wind puts the house under constant pressure. The proverbial tornado from the socket outlet impacts the comfort of a room considerably. Air drawn in through leaking gaps moves, as it is heavier, to the deepest point in the room, that is the floor. Permanent cold feet are the result – a very unpleasant feeling. In this case not even good insulation values to the cellar help if air from outside can enter through cracks in the building’s skin. In addition, the ingress of moisture into the construction can result in structural damage and even the sound protection is reduced.
Wind-tightness tested to standards
The wind-tightness of a building is stipulated in directive 6 of the OIB (Austrian Institute of Construction Engineering). In Germany the design of the underroof is regulated in the ZVDH (Central Association of the Roofing Trade) directive.
On the outside the construction must be protected from influence of the elements. On the inside the aim is to prevent the room’s moisture from entering the construction and the insulation at random. The air-tight layer is usually on the so-called warm side of the exterior construction elements. In solid constructions it is usually the indoor plastering that adopts this function but in wooden constructions vapour-retarding sheets are used, for example. The air-tight design of the building’s skin is set out in standards and directives, and for a very good reason. Besides draughts and inferior air quality, poorly designed air-tight levels can result in damage to the construction. When air from the interior passes uncontrolled through gaps into cooler regions, moisture condenses there and mould and rot can easily form.