advanced building skins 14 | 15 June 2012 - lamp.tugraz.at - Graz ...

Advanced Building Skins
As was stated at the beginning, ventilated façades are those enclosures characterized by a
specialization in waterproofing, while the remainder of the functions are entrusted to an inner skin of
prefabricated paneling that recalls traditional construction techniques. Regarding this inner skin,
however, there have been few occasions on which specialists have reflected on what these
functionalities are and what the best way to satisfy them is. For this reason, it is precisely such a
functional analysis that we are interested in, and which will serve us as a guide vis-à-vis the taxonomy.
4.2 Separation of the Functionalities from the Inner Skin
The objective of this taxonomy is to categorize the possible solutions for load-bearing inner skins in
ventilated façades based on the remaining functionalities they must fulfill.
The maximum concentration supposes the satisfaction of five basic functionalities, subsequently to
which these functionalities are separated into specialized layers. These layers are themselves resolved
by specific elements designed for precisely such a purpose, whereby the resolution of these
functionalities ceases to be the responsibility of the load-bearing element.
It is possible that as the number of functionalities separated from the load-bearing skin increases, they
end up being resolved by a single layer adjacent to the latter. In such a case, separation would not be
accompanied by specialization, but would instead have produced a regrouping of functionalities
around a different element than the one focused on in this study. Insofar as what concerns us in this
study, these would be functionalities that had been “expelled” from the panel and would thus have no
impact on the definition of the latter.
4.3 Sequence of Separation
The progressive separation of functionalities does not automatically yield functional types. Instead,
these depend on the range of possible combinations in which the functionalities can be grouped in the
panel. A panel can satisfy the functionality of thermal insulation without being fireproof, or vice versa.
There is no a priori determined order to which functionalities should be separated first.
Despite the fact that five functionalities have been taken into account in developing the taxonomy, the
possible combinations should not include them all.
Load bearing
The load bearing functionality is indispensable, as it is a characteristic of the element being studied.
This functionality is the only one that can be resolved by means of a discontinuous panel. This
discontinuity can yield a variation in the thickness in section or an alternation of solids and voids.
The load bearing functionality is not always located in the inner skin. Wind load can be deflected by
the outer skin, by resorting to supports of a lesser mechanical capacity to make up the structure of the
inner skin. There is also the possibility that this breaking down of the load bearing element can be
carried to an extreme, whereby by substructures appear for the different layers forming the enclosure.
Still, breaking the load bearing functionality down into substructures, or even relocating it to the inner
skin does not simplify the design of the enclosure. As has been stated above, this has been taken as a
defining characteristic of the inner skin panel in this study.
Airtightness
Airtightness is a basic condition for achieving thermal insulation, fire retention and acoustical
reduction. As such, it cannot be separated unless all three of these have already been delegated to
another element beforehand.
Acoustical
The acoustical functionality requires a minimum value for the massing. If this is not met, a
discontinuity must be established between whatever sheets make up the panel. If the panel has an
adequate section so as to satisfy the functionalities of thermal insulation and fire retention, it will
typically also provide for the necessary degree of acoustical reduction, either by dint of its mass or the
succession of layers.
According to the Law of Mass and as is stipulated in the CTE, a mass of 43 kg/m² is sufficient to
provide the necessary 32 dBA of insulation. This mass can be achieved with a 3-cm-thick material of a
density of 1,433 kg/m³, 5 cm if the density is 860 kg/m³ or 8 cm for 538 kg/m³. These densities could
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