In order to understand façade construction, a detailed picture of the objectives a façade is actually built for needs to be sketched. Cross (Cross, 2008) describes the ´Objectives Tree Method´ as a ´brief´ for a design problem. Objective trees are also called ´function trees´. They basically are a list of desired product functions on general and more detailed levels. Whereas in the field of product design, a function tree is generated in order to set the foundation to create a new product, the goal of this part is to develop a more or less complete tree of façade functions that can serve for the analysis of façade construction in chapter 6.
This can be done by drawing function structures as described by Ulrich.
The above analysed literature gives examples of how functions are defined and how they can be categorised.
§ 4.4.1 Function as defined in the field of product design
Eekels describes function as follows: “The function of a product is the intentioned and conscious attached ability to transform the material environment of the product”. Thus the function says something about the desired behaviour of a product.
Simplified, Eekels and Cross as well as others describe functions in form of a ‘black box’. It contains all the functions that are necessary for converting the inputs into the outputs.
Function Outputs
Inputs
‚Black Box‘
Figure 39
´Black box’ system model according to Cross
In contrast to a property that a product has independently from the goal of the user, functions can be described as requirements that a product has to fulfil.
In this context, Poelman introduces the term ‘functionalities’ to describe function. “A functionality is defined as ´something´ that a technology can perform. …a function is defined as a set of functionalities which are deployed for some objective (Function = functionalities + objective)”. An example to illustrate the formula: A façade function would be supplying the interior of the building with fresh air (ventilation). An operable window is a functionality that could be used for this purpose. (Ventilation = operable window for the purpose to let air penetrate the building envelope). The function could also be fulfilled by different façade functionalities with the same objective (e.g. mechanical ventilation unit) and the operable window can be used for different objectives such as window cleaning.
Poelman has designed a method for defining functionalities - properties that can be used to fulfil a product function. It is an extensive procedure involving several steps with assignments and simulations. Applying it to the purpose of this chapter (the analysis of façade functions) would go beyond the scope of this work. Nevertheless, Poelman has categorised types of product functions that are very useful for the purpose of this dissertation:
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Primary and secondary functions•
Primary functions and support functions•
Positive and negative functions•
Functions meant for different users•
Technical and emotional functionsSecondary functions are applications of a product other than the primary function.
For example, an umbrella does not only protect against rain but could also be used to defend oneself against attacking dogs. Support functions enable the primary function:
An umbrella needs a handle to be carried around.
In addition to the intended end user, others usually have to cope with a product as well;
such as manufacturers, transporters, retailers, recyclers and others. This can have a big influence on the product itself, for example on packaging. It is interesting that the literature on façades does not pay much attention to the end user (primary user). The end user is seen as an observer of architecture, or a user of the space behind the façade where he or she can expect a defined climate and change sun-shading settings or open windows. More attention is paid to the builder (building process), investor (costs) or the architect who is interested in the design possibilities and minimising of failures.
Every product has negative side effects. A negative function, for example of a car is the use of energy with its bad effect on our environment. It is therefore necessary to pay attention to these types of functions. The fuel consumption of cars today has become a primary decision factor for many end users. Negative functions in the field of façades are equally inevitable. A sun-shading device can block the view considerably, and reduce the ability to exploit day light. Whereas climate designers embrace sun shading systems, architects are usually very sensitive about the way they affect the design.
Technical (objective) and emotional (subjective) functions require thorough attention.
The way in which a product fulfils its technical function can be measured. This is more difficult with emotional functions since they depend on the subjective perception of the user. Personal mental experience has a large influence. A product can perform well technically, but still might not be generally appreciated. Virtually every product includes some degree of technical and emotional functions. Poelman gives good examples to illustrate this point. Ball bearings, for example, must primarily fulfil technical functions. A car, on the other hand, needs to satisfy both technical and emotional functions, since its market success depends on technical quality as well as on image, beauty etc. Jewellery primarily satisfies emotional functions. In the context of façade construction emotional values are mostly achieved by architectural design.
§ 4.4.2 Function in façade related literature
Examining façade related literature in terms of the above categorised types of functions from the field of product design proved interesting:
In the book ´Façades` (Knaack et al., 2007), functions are described as different requirements a façade needs to fulfil. No further separation into the above
mentioned function types are made. The following functions are mentioned without a hierarchical order:
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Insulation against heat, cold and noise,•
waterproofing•
providing natural light for the interior,•
protection against light,•
resistance against wind loads, interior loads and self-weight,•
vapour management,•
visual contact to outside and inside•
architectural appearance.All these different kinds of functions are named on the same level. For optimal
functioning, the façade should thus not be a static construction but change in response to influencing factors. Therefore, adaptability should also be included in the list of functions.
Figure 40
Requirements on façades according to Knaack
Rentier, in his book, divides functionality into primary function (separating the interior from the influences of the outside - rain, wind, heat, cold, noise, and burglary, etc. -) and secondary function which provides information about the function or the owner of the building and could be translated with architectural intention of the façade. It is interesting that the book emphasises technical functionalities. This attitude can be explained with the technical background of the book. An architect would typically choose the opposite order by emphasising emotional functions (architectural design).
Figure 41
Requirements on façades according to Herzog (Herzog et al., 2004) The scheme is reproduced in a shortened way.
The ´Façade Construction Manual´ gives an interesting representation of façade functions.
The overall façade function is defined as follows: “The façade is a separating and filtering layer between outside and inside, between nature and interior spaces occupied by people”. A graphical scheme is chosen that includes the outside and inside of the building as well as the façade as separating component. The requirements of the inside (this corresponds to the actual façade functions according to Poelmans concept) result from external conditions that are specific to the location. To fulfil the requirements, Herzog gives the façade protective and regulatory functions (passive or active
constructions). In the above discussed context the term functionalities would be more appropriate.
Supplementary measures such as sun-shading devices or blinds on the inside or outside can enhance façade functionality. It is interesting that the author also includes building services as supplementary measures if the façade alone cannot deal with the outside conditions. These can also be located outside, in the interior, or on the inside of the physical façade construction.
Herzog also makes a first step to lay the link between aspects of the façade and its geometry. Aspects are points of consideration. For him “Façades are primarily vertical and planar …. structures positioned between the external and internal environment”.
But still, the third dimension of the façade still serves special purposes. He writes:
“Aspects to be considered in the plane of the façade:
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type of surface•
allocation of performance profiles•
load bearing ability•
design principle•
jointingAspects to be considered perpendicular to the plane of the façade
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realisation of the performance profiles•
construction in terms of layers and leaves•
joining of layers and leaves”The term ´performance profiles´ is not further defined. It could be interpreted as follows: the decision of where façade functions should be located is made in the plane, and the realisation of the desired functionality happens perpendicular to this. For example the level of insulation: It is located planar, but its performance depends on the third dimension; the rule is the thicker the better. The construction façade needs joining in three dimensions.
§ 4.4.3 Summary
Functions are essential when analysing or developing products, or in this case curtain wall constructions. Literature in the field of building technology provides us with a basic list of potential façade functions. However, the behaviour of a product on the market is determined by the way parts, components and elements are arranged and connected, and more detailed understanding of façade functions is required to develop a function structure, for example. The field of product design discusses functions more in-depth.
In this research, the theory about functions is only presented briefly, but it provides a valuable vocabulary:
•
A function is defined as a ´black box´ converting the inputs into outputs.•
Poelman specifies this: A function is defined as a “set of functionalities which are deployed for some objective (function = functionalities + objective)”.Poelman further defines different types of functions:
•
Primary, secondary and supporting functions.This can be explained with façade construction terms: If the creation of a durable construction is the primary function, one of the secondary functions is enabling water and vapour management within the construction. This is supported by the function of allowing an interior drainage system.
•
Positive and negative functions.Whereas a positive façade function can be the reduction of heating energy demand, a negative function is that a façade will have to be disassembled, recycled or put on the landfill at the end of its lifetime.
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Functions meant for different users.It is clear that certain parts of a construction will always be dedicated to enable an efficient construction process - a function that does not concern the end user of the building.
•
Technical and emotional functions.A technical function can be measured, such as the insulation of a façade; whereas emotional functions are represented by architectural design or haptic qualities.
The role of different function types becomes clear. When analysing (and developing) façade construction, one should be able to allocate certain components to the function types as mentioned above. To clearly understand or improve a construction, we need to be aware which parts, components and elements are related to the builder or the user of a façade; and which relate to technical or architectural functions
Side note