We can distinguish the various material form of the supporting element of the façade when reaching its position in the building under construction (amorphous, small elements, components and semi-finished products), with all the consequences that this form has regarding the construction techniques, the building or assembling process, type of unions or fixings, and so on.

We can distinguish the two ways of achieving water tightness: material barriers and geometric mechanisms that use gravity to bring water to the outside, usually with the collaboration of a drained cavity. The drained cavity, inherited from the “tabique pluvial” and the Anglo-Saxon “cavity wall”, is a barrier that achieves water tightness simply by reducing the volume of water that penetrates this cavity and evacuating it through gravity and ventilation. It is therefore a ventilated cavity, but that name suggests efficiency in the evacuation of thermal gains from sun exposure. This efficiency is difficult to demonstrate in real cases, where cavities have a maze of mounting rails, little thickness and a poor design of the air inlets and outlets.

We can distinguish supporting elements that also fulfil water tightness, either because of its own characteristics, or due to those of a finishing material applied directly – a render or any other type of covering; from those where water tightness is achieved with additional elements added fixed over the supporting element as new layers of significant scale. This distinction brings with it a series of determinant factors for the entire enclosure system. One of these is the direct effect on the position of the insulation, given that if the supporting layer is not watertight, and therefore requires the external addition of a new layer, this new layer enables the insulation to be hidden on the outside of the supporting element. If it is the supporting layer element which provides water tightness, the facade can only expand towards the interior, and therefore the insulation must be positioned on this side of the enclosure.