Principles of Enclosure

This contribution to Architectural Science Forum builds on its predecessor, “Perspectives on Sustainability” (see CA January 2002). Concerns for sustainability demand that we consider the fundamental requirements of buildings and re-examine our current approaches to building envelopes and environmental separation. Some observers have expressed concern that perhaps we have gone too far in separating ourselves from nature. If architecture intends to attain sustainability, it is important to start by looking at the idea of enclosure because it drives so many other performance parameters for buildings.

Enclosure has many meanings. It represents a fundamental construct in architectural design pertaining to the representation of spatial arrangements. Through the materialization of basic geometric entities–points, lines, planes and volumes–architecture arranges program across a rich spectrum of expression, ranging from the subtle and suggestive through to the explicit and absolute. Listening to any discussion of architectural design, virtually all of the terms used to describe spaces, places and their connections are premised on the concept of enclosure.

From an architectural science perspective, enclosure represents a necessary but insufficient condition for effective moderation of the environment. For buildings to achieve acceptable, preferably optimal performance from their envelopes or skins, the principles underlying their performance must be clearly understood. Equally as important, the architectural design intent must be sufficiently declarative to guide the selection and manipulation of enclosure elements so that aesthetics are harmonized with sustainability criteria for both the building envelope and the whole building system.

It has been estimated that on average Canadians spend approximately 90% of their time indoors. The idea of enclosure as shelter, or protection from the elements, must be reconciled with our need to remain connected to nature and gain access to light and air.

Enclosure Requirements

The performance requirements for enclosures have been well understood for several generations. Neil Hutcheon, one of the pioneers of Canadian building science, established a set of minimum requirements almost half a century ago.

Since the time Hutcheon outlined these requirements, some of the terms used have taken on new meaning. Control of heat flow now fully considers solar radiation in terms of daylighting and passive solar heating. The stability and durability of materials includes issues such as off-gassing of contaminants, moulds and embodied energy. Cost has been generalized to consider the environmental impacts of buildings. The biggest changes regard aesthetic considerations, in particular thermal comfort, indoor air quality, and auditory separation.

It is not surprising that Hutcheon defined a basic set of performance requirements which extend from the Vitruvian parameters of commodity, firmness and delight; the needs and desires of humans have essentially remained constant, as have their reasons for, and methods of, constructing enclosures. One aspect that has changed to some degree is the imperative for sustainability. We have evolved to the point where survival deals less with protection from the natural elements, and more with managing our ecological footprint and the health and well-being of building occupants.

Enclosure Typologies

In addressing the new challenges associated with enclosure, it should be recognized that there are few significant differences between how we build today and how our ancestors built several thousand years ago. While modern buildings may be bigger, taller, stronger and built faster, they are not fundamentally different. Based on the physiological, psychological and social needs of people, the principles of building enclosure have not changed at all. But the cultural context of architecture has continued to evolve, and it is useful to explore the common tectonic thread which binds past, present and future.

Traditionally, enclosures are either monolithic or composite assemblies. In monolithic enclosures, such as load-bearing masonry, a single material may act as the structure, the cladding and the interior finish. The control of heat, air and moisture flow that resulted was incidental. Composite assemblies generally assign critical control functions such as the control of heat transfer or air leakage to separate materials, or combinations of materials.

The triumph of modern architectural science is the rejection of the incidental quality of environmental separation provided by traditional building materials and assemblies in favour of a deliberate selection and arrangement of materials according to their intended function in response to physical phenomena. However, it is important to appreciate that our scientific sophistication has not appreciably displaced enclosure tectonics.

Building enclosures may be simply classified by examining the tectonics related to their structure, cladding and interior finishes. Structures consist of stacked units; frames; shells and plates; and air-supported fabrics. Claddings and interior finishes involve wet coatings, discrete units or panels; fabrics, films, sheets, rolls; and the incidental outcome of monolithic construction.

Most modern buildings involve hybrid arrangements of basic building techniques that have not fundamentally changed since the time we abandoned trees and caves to fashion artificial shelter. The next challenge is to encode new science within inherited tectonics, so that having mastered the compulsory elements, we are free to explore artistic expression within a broader canvas of appropriate ecological adaptation.

Limit States Design

While the tectonic basis of enclosure has not changed significantly over time, our understanding of building envelope performance has made dramatic advances. Practicing architects frequently remark that due to local construction conventions, many envelopes have been overbuilt, thus providing a much higher factor of safety against performance problems than is required in a particular climatic location. In other cases, evidence suggests that building envelopes have been under-designed, most frequently causing severe moisture problems compromising the integrity of the enclosure.

A recent development in architectural science borrows from structural engineering and involves the application of limit states design theory to the design of building enclosures, implying that concepts of load and load resistance are as applicable to moisture protection as they are to structural design.

Dr. Joseph Lstiburek of Building Science Corporation in Boston advocates that we consider rain, temperature, humidity and the interior climate as environmental loads, the limit states of which are decay, mould and corrosion.

The limit states design of moisture protection for enclosures would consider the probable exposure to moisture based on the following conditions: the regional climate and weather; site influences, such as terrain, orientation, exposure and adjacent structures; building geometry, roof and faade features; and the use of the building. For instance, it should be expected that a swimming pool enclosure in Yellowknife would differ significantly from a warehouse enclosure in Windsor.

It is important that architectural science seeks to address issues related to the predictable durability and performance of building enclosures so that we know what to design. No less important is the question “what should we design?”

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, fails to 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 int
eractive 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 come to a sudden halt, we could continue to explore the 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.

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.

Enclosure as environmental mediator is premised on peoples’ relationships with the outdoors and each other. Are today’s buildings too static and inflexible? 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.

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.”

Coming in May 2002

The next edition of Architectural Science Forum, “Building Envelope System Performance,” will provide a contemporary review of envelope system design parameters and some of the tools available to assess performance at the design stage.

Ted Kesik is a professor in the Department of Architectural Science at Ryerson University and Visiting Associate Professor in the Faculty of Architecture, Landscape and Design at the University of Toronto. The full electronic version of this article is available on the Web at under Architectural Science Forum. This forum is intended to facilitate the exchange of knowledge and information pertaining to architectural science among practitioners, researchers, academics and students of architecture and its allied disciplines. For further information on submissions to Architectural Science Forum, contact the editors.

Major Considerations

A list of all the possible specific requirements of walls might be of little value. Many items in such a list would apply only in special cases. The majority of the items would not be provided for intentionally in most designs, but would be satisfied incidentally.

The major considerations that should be recognized in the design of walls for Canadian conditions are as follows:

1. Strength and rigidity.

2. Control of heat flow.

3. Control of air flow.

4. Control of water vapour flow.

5. Control of liquid water movement.

6. Stability and durability of materials.

7. Fire.

8. Aesthetic considerations.

9. Cost.

Excerpted from Fundamental Considerations in the Design of Exterior Walls for Buildings, N.B. Hutcheon, Technical Report No. 13 of the Division of Building Research, National Research Council Canada, Ottawa, 1953.