envelope requirements

*Functions of a Wall [Excerpt from Hutcheon 1963 R-143]

The over-all function of an exterior wall, in conjunction with floors and roofs, is to provide a barrier between indoor and outdoor environments, so that the indoor environment can be adjusted and maintained within acceptable limits. The requirements for a wall must, therefore, relate to its ability to remain in place and to be durable for a required length of time, while providing the necessary barrier or filter to wind, rain, solar radiation, heat, noise, fire, particulate matter, insects, animals and even humans. It may be required to transmit light (windows), while imposing a barrier to other factors; must not itself be a hazard to life or property; must contribute suitably to the form and aesthetics of the building generally; and finally must satisfy a number of lesser requirements such as colour, texture and porosity. All of this must be achieved as far as possible at an acceptable cost, including both initial and maintenance costs.

Principal Requirements of a Wall

1. Control heat flow;

2. Control air flow;

3. Control water vapour flow;

4. Control rain penetration;

5. Control light, solar and other radiation;

6. Control noise;

7. Control fire;

8. Provide strength and rigidity;

9. Be durable;

10. Be aesthetically pleasing;

11. Be economical.

Exterior Wall as a Barrier

The elements of the wall must be selected so that in the first instance they impart the necessary resistance to keep heat, moisture, air and other flows within acceptable limits. The way they are arranged, however, is also important; this will determine the variations in conditions throughout the wall. These provide the environment in which the various parts of the wall must continue to function, and are seldom linearly graded from, outside to inside. Interactions between the various factors involved may produce conditions within the wall that require special attention. Some understanding of the phenomena involved is therefore necessary so that they can be judged quantitatively and wall designs evaluated.

The differences in the properties of inside and outside atmospheres to be separated by a wall dictate the requirements of that wall. In combination with the properties of the materials to be used, these differences determine the environments within which each element must perform. The service life of a material is determined by the properties of the material and the conditions of the environment to which it is subjected.

Durable walls can be achieved by judicious selection of materials to suit the environment, by modification of the environment to suit the materials available, or by a combination of both. Such manipulation, however, requires an understanding of the pertinent properties of materials and the phenomena that operate within walls.

The new sustainability wave:

Building and its envelope are further judged by Energy Efficiency, Resource efficiency, environmental responsibility, occupant health, and affordability.

Residential Energy Code - Seattle

10 Chapter, HTML format, interlinked.

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Multicriteria interactive tool to sketch the building envelope during first stages of architectural design, by Hauglustaine, J.M, 2001

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ORME: A multicriteria rating methodology for buildings, by Roulet,C. -A., F. Flourentzoua, H. H. Labbena, M. Santamouris, I. Koronakib, E. Dascalakib and V. Richalet, 2002

basic requirement

Requirements for Exterior Walls, by Hutcheon, N.B, 1963

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Walls and Infrastructure, by Duncheskie, D., Coleman, J. and Oddo, V., 1998