Usage of term “envelope” related to architecture is quite recent and comes from an evolution of the concept of closure that identifies, as different units, exterior vertical and horizontal partitions. Within modern building concept the envelope, referring to the whole building closure system, “frees itself of the historical role of barrier defending against climatic agents and identifies itself as a skin, such a breathing thing which regulates – according to the widest meaning of this word – communication dynamics with the exterior viewing the building organism that, as well as a living being, lives on the exchanges, either direct or figu-rative, with its own environment”.
Actual conception of building envelope has its origins in Reyner Bahnam work which, yet in 1969, introduced the idea of “well tempered environ-ment” and assigned to the envelope a fundamental role in determination of that condition. Analyzing architecture history, Bahnam individuates three pri-mary model of environmental control each associated to an envelope typology with specific characteristics: conservative, selective and regenerative. The conser-vative model is characterized by an environmental control using large massive walls with few openings in order to reduce thermal dispersions in cold climates and, at the same time, reducing to attenuate warming effects due to solar radi-ation in warm climates (or periods). The second model, called selective, is par-ticularly suitable for warm–humid climates and is characterized by general principles analogue to the previous one, but “uses the structure not only to preserve desired environmental conditions, but to allow the entering of those conditions from the exterior too”.
1University of Camerino – Eduardo Vittoria Architecture School of Ascoli Piceno.
Taking part in preliminary works and in paper writing: Sonia Calvelli e Federica Ottone (tutor) con i dottorandi Maria Teresa Cusanno, Matteo Iommi, Angela Leuzzi, Laura Ridolfi, Irene Virgili, Luca Frattari, Nazzareno Viviani.
Massimo Lauria (edited by) Produzione dell’Architettura tra tecniche e progetto. Ricerca e innovazione per il territorio = Architectural Planning between build and design techniques. Glocal oriented research and innovation, ISBN 978-88-8453-988-5 (online) ISBN 978-88-8453-990-8 (print) © 2010 Firenze University Press
For that purpose large transparent walls may be previewed for illumination and passive warming.
The third model, the regenerative one, characterizes those buildings with no massive walls in which environmental control is totally deputed to installed sys-tems, aksi defined as regenerative installations, while the envelope is intended to be a barrier able to limit interior–exterior interactions.
Most recent technological researches delineate an innovative vision of building envelope thought not just as the architecture card, but as a “complex filter–system, selective and multi–purposed” which, more than sepa-rating two environments, is able to control and modulate interactions and inte-rior–exterior exchanges. It flexibly reacts to variability of environmental con-ditions, minimizing thermal dispersion during winter period and limiting tem-perature raising during summer one, with a consequent enhancement of inter-nal comfort and user life quality obtained with no use of non–renewable ener-getic sources. In order to satisfy those needs, in building modern concept, the envelope has progressively lost its condition of uni–material element, trans-forming itself in a complex functional system, articulated in several layers and materials with specific features. It’s required, during design and realization processes, different competences and specific knowledge along with a ever increasing capability of the architect of managing relation with other systems (structure, plants, functions, etc) which define the whole building organism.
Starting from the fundamental role of the building envelope, not only in formal and expressive definition of architectural artifact but principally in determination of energetic requirement (more and more necessary according to ever more tightening norms), many researches in technological and building physics fields have addressed their scope to the development of envelope systems with high energetic performances and able to guarantee good levels of thermo–hygrometric, visual and acoustic comfort.
From present researches and experimentations in the field of technological and environmental design two big envelope categories seem to come out, based on two different behaviors from a cultural point of view more than a technical one:
massive envelope system and multi–layer dry envelope systems. First ones commit interior climatic conditions control to mass and width of one or two homogeneous high–density materials. The other ones, constructed by assemblage of light ele-ments, commit their whole performances to specific characteristics of each single component layer. In such case, designing envelope system requires a high knowl-edge of performance behavior of every single material and component employed, because it is possible to get high performances only optimizing and specializing the layers constituting the envelope system.
187 The envelope as an architectural interface
Beyond the underlining of traditional dichotomy heavy–light, the two approaches highlight differences both in the relation between whole sustainability of building intervention and technological innovation, and in a renewed meaning of the “context” concept. Dry multi–layer envelope systems, in fact, designed as a dynamic interface and the environmental exterior conditions are considered as a resource and not a force to fight with: building envelope gains, in this way, the function of “a reactive skin that protects interior from atmospheric agents but, at the same time, it takes functionally advantage from their power; a sensible skin that evokes many changes possibility”.
Most studies on new envelope typologies refer to scientific literature, research-es, case–study and experimentation carried on last decades mostly within cen-tral–Europe culture (Germany, France, sud–Tirol, etc.); there are still few stud-ies purposing to treat, with the same scientific and methodological rigor questions posed by the relation between building envelope and context (physical, geographi-cal, cultural, technigeographi-cal, etc.) at the Mediterranean latitudes, with the aim of for-mulating new performance parameters and new verification tools which are coher-ent with the peculiar environmcoher-ental conditions that these contexts offer.
Setup and verify of energetic performance of dry multi–layer envelopes became the major field of interest of a growing number of doctoral research which, together with specialist field of study external to architecture discipline (thermo–physics, acoustics, material science, etc), reached interesting scientific results. Those researches posed to the attention of scientific community new question concerning the development of new specialist figures (such as the clima–designer) able to control with high competence aspects related to energetic and environmental functions in a building but committing to other designing figures the whole coordination of design process. This one, in fact, has an holis-tic nature which does not allow to neglect or ignore effects induced, by an sepa-rately designed envelope system, on the whole architectonic artifact.
In the same way, on the other hand, it is not possible to ignore feedbacks on formal and expressive quality from technical choices that, although correct and coherent with scientific data of a given problem, should be always be con-sidered partial and functional with respect to achievement of higher and high-er levels of architectonic quality.
The envelope, considered as an architecture interface, a border sensible to innovation and not only frontier between interior and exterior, may become a place of meeting among different qualities (spatial, environmental, functional, technological, constructive, formal) that have not just to be measurable and ver-ifiable on the basis of performance parameters but they should come back and take part of thoughts on tectonics and meaning of contemporary architecture.
MARIACRISTINAFORLANI1