Enclosure as Environmental Mediator
The fundamental concept of enclosure may be architecturally complete, but does not explicitly address critical control functions (i.e., the control of heat, air and moisture flow). The traditional building science approach to enclosure, commonly referred to as an environmental separator, does not deal with many desirable interactions with outdoor environmental phenomena. Design thinking is rapidly moving toward the idea of enclosure as an environmental mediator - not purely passive and restrictive, but interactive and selectively accommodating. Within the next generation, we will largely possess material technologies and predictive design tools that promote discriminating environmental mediation which addresses aesthetic and sustainability objectives.

It may be reasonably argued that if all advances in materials technology were to suddenly halt, we could continue to explore vast possibilities afforded by that which we already possess. Similar to the world of computing, where hardware is clearly ahead of software, architecture has yet to fully explore the contemporary palette of materials - glass being among the more notable examples of the opportunities awaiting innovative minds. With our improved understanding of architectural science, and the development of liberating glazing materials, the control of solar radiation awaits its reinterpretation within modern architecture.

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Bioclimatic Considerations
In order to achieve effective environmental mediation, it is necessary to consider not only the climatic factors discussed in the previous section on limit states design, but also the fundamental phenomena of sunlight and air movement. The use of a sun path diagram is a convenient means of orienting buildings and contemplating fenestration strategies.

Local wind data can also be researched to determine how natural ventilation may be combined with daylighting through operable windows and intentional openings. Wind data may also inform the landscape design process to improve thermal comfort and minimize undesirable snow accumulations due to drifting. It is important to recognize that for natural ventilation strategies, the primary drivers are wind and stack effect. Stack effect is most effective during cold weather when a high indoor to outdoor temperature difference is available. During summer months, wind driven ventilation requires an average wind speed of at least 2.5 m/s to prove feasible. The site specific nature of wind effects requires careful and costly analysis coupled with sophisticated numerical and analog modeling of natural ventilation strategies.

The original British Museum Reading Room, built in 1857, provides an early example of wind-driven natural displacement ventilation. Its dome-shaped roof is vented at the top, and the negative pressure here will naturally draw the warm air out of the room. The negative displacement within the room will in turn draw air in from the courtyard to the basement, where it is distributed via underfloor vents. The thermal capacity of the walls in the basement enables the air either to be cooled or warmed, depending on the season, before entering the Reading Room. [Battle McCarthy Engineers]

Today, classical cupolas are being displaced with aerodynamically designed wind scoops which are connected to a plenum of inter-connected interior spaces that facilitate natural ventilation.

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New Developments
Enclosure should also be considered to extend beyond the building envelope to address the transition from personal to community space, and from artificial to natural environments. The use of landscape elements to modify the environment is ancient in origin. In the 1960s Victor Olgyay,
among many others, investigated bioclimatic design for comfort and energy efficiency. Today, we know that a single layer of insulation can impact energy efficiency to a greater extent than landscape interventions. However, in the mediating zone between indoors and outdoors (or between internal zones of a building), comfort and delight can be achieved through the subtle
manipulation of soil, plants and water.

Important questions arise when architecture, landscape and urban design are considered as nested layers of enclosure. Are today's building too static and inflexible? Enclosure as environmental mediator is premised on peoples' relationships with the outdoors and each other. Looking at the constricting enclosures of conventional office workers' cubicles, squashed between absolute floor separations, and banded by inoperable windows, the answer is painfully obvious.

There remains much cause for optimism despite the numerous criticisms leveled against modern architecture, particularly as it is revealed through enclosures. Experiment with kinetic enclosures, hybrid ventilation systems, enclosures which control light, sound and privacy are among the many advances that regrettably populate only a small minority of today's buildings.

Modern architectural science is accelerating the evolution of enclosure from a monolithic barrier, through a functionally delineated, composite assembly, and beyond to a fully articulated transition from indoors to outdoors, or between adjacent internal spaces. As we evolve our sense of enclosure, it is being discovered that architecture can promote human health, well being and productivity without squandering our limited resources and devastating the ecosystems which support life.

Reinvigorating our principles of enclosure transcends the realm of environmental separation where we seek to control phenomena that threaten our primordial notions of shelter. It demands that we recognize architectural enclosures as more than physical assemblies, or as Thomas Berry has observed, "not a collection of objects but a communion of subjects."

A delicate screen made from aluminum tubes provides privacy and shelter while admitting diffuse light across a range of sun angles in this office and commercial building in Tokyo, Japan.	Inflated ETFE cushions provide a lightweight alternative to glass in the Eden Project located in St. Austell, U.K.
Adjustable louvers and shading fins provide control of direct and indirect daylighting of this building in Wiesbaden, Germany by Herzog and Partner. The next section on Related Resources provides links to sources of information supporting principles of enclosure.	Articulation of structure and cladding are depicted in this interior view of the Japanese Pavilion in Hanover, Germany by Shigeru Ban.

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