Architects’ considerations while selecting materials

Materials and Design 34 (2012) 584–593

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Materials and Design journal homepage: www.elsevier.com/locate/matdes

Architects’ considerations while selecting materials Lisa Wastiels a,b,⇑, Ine Wouters a a b

Department of Architectural Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussel, Belgium Department of Architecture, Urbanism & Planning, K.U. Leuven, Kasteelpark Arenberg 1/2431, 3001 Leuven, Belgium

a r t i c l e

i n f o

Article history: Received 16 September 2010 Accepted 9 May 2011 Available online 19 May 2011 Keywords: H. Selection of materials E. Properties of materials

a b s t r a c t When selecting materials for a building, architects are guided not only by structural and functional requirements but also consider aspects relating to the sensory effect and experience. The material information and selection tools available for architects are, however, often dominated by technical material data without providing systematic knowledge on experience aspects of materials. Hence, no comprehensive material information is available to the architect. This paper aims to identify, organize, and map the different elements contributing to the material selection process for buildings, and generate a schematic of basic material selection considerations for an architectural design project. The paper discusses the findings of three studies investigating architects’ materials selection process at different stages of the design process. As a result, architects’ materials selection considerations are identified and organized according to four categories: Context, Manufacturing, Material aspects, and Experience. These considerations are discussed in relation to each other as well as in reference to material selection research in architecture and industrial design. The results confirm the importance of aspects relating to experience in an architectural material context and emphasize the need for further research and information on the topic of material experience in architecture. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Nowadays, an increasing diversity of materials is available for the buildings architects design. To choose among this enormous amount of materials, the architect has to take into account several design criteria. The consideration of properties related to perception, as well as ecological, economic and technical properties, and those related to use are basic issues of materials selection [1,2]. In general, every material selection process aims to fulfill a simple need, identifying the best material for a particular application [3]. In order to identify what a ‘‘best’’ material can be, it is important to understand what aspects are at play while architects are choosing materials. The existence of numerous sources providing information on materials’ technical properties suggests that the technical behavior comprises the primary medium for comparison and final determination of material decisions. Numerous architecture projects, however, illustrate that the choice of materials does not only define the structural possibilities, but also determines the character of the building. While selecting a material, the architect looks into performance aspects such as the material’s durability or compressive strength, but also considers aspects that concern user experience ⇑ Corresponding author at: Department of Architecture, Urbanism & Planning, K.U. Leuven, Kasteelpark Arenberg 1/2431, 3001 Leuven, Belgium. Tel.: +32 16 32 13 34; fax: +32 16 32 19 84. E-mail address: [email protected] (L. Wastiels). 0261-3069/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2011.05.011

or sensory stimulation, such as color or texture. Moreover, the architect might have a certain atmosphere in mind that will be reflected through the materials, such as a ‘formal’ feeling for a lawyer’s lobby, or a ‘trendy’ feeling for a lounge bar. The wide variety of roles that materials play in architecture is discussed in several sources and it becomes clear that choosing materials for an architecture project is not only about meeting the structural requirements, but that the material’s appearance and sensory behavior play an equally important role while designing [1,4,5]. 1.1. Material experience in architecture Considering the importance of the experiential qualities in architecture, it is surprising that there is so little explicit knowledge about this fundamental characteristic of architecture. Where technical designers readily have access to information of the sort they need, industrial designers express frustration about the level of available information support [1]. Architects typically use the technical data provided in material data sheets to verify the material’s physical behavior, while using physical material samples to explore the material’s sensory qualities, including its appearance. Material consulting companies for architects and designers, such as MaterialConneXionÒ [6], MateriaÒ [7], and MateriOÒ [8], emerged across the globe over the last decade, offering physical material libraries to their clients for material browsing. These libraries are mainly focused on intuition by offering material samples, in combination with some basic technical and

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manufacturing information. This way, they contribute to the intuitive material browsing, but they do not provide systematic information on the qualitative aspects of materials. Moreover, the materials presented in these libraries are mainly selected based on their opportunities for innovation and creativity, and thus do not provide a more general material overview. The number of books and websites focusing on the different aspects of materials in a design context keeps growing as well [9–12]. These recent sources show increased attention for the experiential aspects of materials, but the information is limited to an occasional description of the material’s appearance without providing a clear and comprehensive overview that might be useful to architectdesigners. Apparently, there is a lack of clearly described, comparable definitions of material experience aspects. Hence, no comprehensive material information is available to the architect. The main problem is the lack of objective information or well-founded systematic knowledge on the experiential qualities of materials. This lack of parameters describing the sensory, perceptual or experiential aspects of materials prevents architects from comparing new materials to familiar ones and results in a knowledge gap. 1.2. Material experience in product design Whereas experience aspects are only starting to gain interest in architecture, the effect of materials on users’ experience and perception has been studied more elaborately within the discipline of industrial design. Industrial design is a ‘‘faster’’ discipline for detecting such trends, because of the smaller scale and shorter develop-to-market times. As the supply of products exceeds demand, products have to differentiate themselves from other products on other aspects than functionality and use. Consumers buy things because they like them. A product thus has to function properly, but must also have a personality that satisfies and gives delight [1]. This is where ‘product experience’ comes in [13,14]. The discipline of industrial design has acknowledged the importance of sensory aspects, user experience and emotion. Product experience is a relatively young, but rapidly growing field of research within the discipline of product design. Numerous studies focus on the sensory experience of products, the attribution of meaning, and the generation of emotions [15–18]. More specifically for material experience, several researchers have identified the need for information on the intangible characteristics of materials [19,20]. In products, people do not only concentrate on the physical characteristics of materials but also evaluate non-physical ones, such as sensory characteristics or characteristics of perception [21]. Also, meanings of materials seem to be influenced by a number of material properties as well as the (cultural) context of the individual appraising the materials [22]. 1.3. Material selection process We argue that the consideration of sensory aspects and perception of materials is indispensable during the material selection process in architecture and demands for more structured material information. In order to substantiate this argument, and to relate the different considerations leading to material decisions to each other, this paper investigates architects’ considerations while choosing materials. Before elaborating on the results from empirical studies, we discuss the most relevant findings of other researchers approaching the material selection process from a design perspective. Over time, several researchers investigated the material selection process. Karana et al. [20] provides an extensive review of different sources defining the effective material aspects for the materials selection process, mainly in product design. It becomes

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clear that most of the sources discussing the material selection process take an engineering approach, mainly focusing on the technical performance and manufacturability [23–25]. It is not until recently that the importance of non-technical considerations starts to gain interest, and that alternative approaches such as design for experience or multi sensory design are introduced to the domain of design [26]. Ashby and Johnson state that designers (and architects) need information on the following dimensions in order to make a proper material selection: engineering, use, environment, esthetics and personality [1]. The engineering dimension refers to a material’s technical attributes and enables a safe technical design of a product. The dimension of use concerns ergonomics and aspects related to the product interface. The choice of a material is influenced by the type of user (e.g. design for children or elderly), but also relates to the thermal management and light management. The environmental dimension demands from the designer to reflect on resources and energy consumption, to design ecologically, and to consider the product manufacture and disposal. In short, it refers to the impact of a material on the environment. Finally, the dimension relating to esthetics and personality relates to the stimulation of the senses, to human perception, as well as to the personality of materials. In van Kesteren’s integrated model for considerations in materials selection in product design, materials are represented as one of the six elements considered during the design process [27,28]. The material characteristics are related to the five other elements: manufacturing processes, shape, function, use, and product personality, implying that all these elements influence the material choice. Karana et al. argue that the selection of appropriate material(s) for designed products occurs by considering ‘‘related design criteria such as manufacturing processes, availability, cost, function, shape, use, as well as meanings, associations, emotions, characteristics of users, and cultural aspects’’ [26]. In the Meanings of Materials model, they clarify that meanings are user and context specific, and evoked by the combination of different properties. In architecture, only limited sources include aspects related to experience to be part of the material selection process. Hegger states that the main criteria for the selection of materials in construction are perception, technical performance, functional attributes, and ecological and economic aspects [2,29]. The technical performance criterion in Hegger’s model includes manufacturing issues as well as the technical behavior of the materials. The perception criterion covers both sensory and experiential issues. The environmental criterion focuses on ‘‘green’’ design, and the economical criterion is added to include aspects such as cost and availability of resources. Fundamental differences exist between the disciplines of architecture and product design, such as the differences in scale between buildings and products, the different kinds of user interaction, or the varying life spans of building projects and consumer products. However, as material aspects related to perception and experience have been researched and developed more elaborately in the context of product design, we will verify whether findings and definitions established within the product design discipline could be relevant in an architectural context. 1.4. The present study This study aims to map and organize the different aspects contributing to the material selection process in architecture, and identify the need for information on material experience. In doing this, the relation between different considerations is investigated and the relevance of material experience descriptions from industrial design is discussed. To achieve this goal, three empirical studies were performed. For the first study, architects were interviewed on finished

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projects. This allowed discussing issues relating to the material choices throughout the whole building process, going from the original design intention, to the final decisions during construction. In the second study, architects were asked to organize their materials selection considerations from scratch, illustrating and organizing all the aspects influencing material choices. As no specific projects were discussed in this study, the findings provide a good reflection of influences at the beginning of the design process. The categorization made by the architects also provides insights in how different aspects relate to each other. In the third study, data of participatory observations of the design process were analyzed to validate and refine the findings from the earlier studies. As a result, different categories of material selection considerations are presented and discussed in detail. Combined together, the three studies complement each other and provide an overview of the aspects important to architects selecting materials, from the design concept phase to the final construction. 2. First study: In-depth interviews What aspects of materials are considered by architects, and what vocabulary do they use to describe them? Are material choices the result of a specific logic and reasoning? Or are choices related to the architect’s personal preferences? Are materials used to materialize certain concepts or desired experiences, and in what way? In-depth interviews were conducted to inquire what aspects of materials architects consider while designing a building, and while choosing its materials. 2.1. Method The in-depth interview was chosen as a method to take the architects back to their thought processes at the moment of designing, by discussing specific projects from their design curriculum. The in-depth interview is an open-ended, discovery oriented method to obtain detailed information, which is ideal for investigating individual interpretations and responses [30]. The use of extensive probing by the interviewer allows the respondent to talk freely. 2.1.1. Participants The interviewees were selected based on their professional experience and the international character of their work. Five experienced architects, four male and one female, ranging between the age of 39 and 60, with 15–30 years of experience, were interviewed individually on at least two of their design projects. Their level of experience ensured their ability to autonomously complete a design process from beginning to end. All participants were based in Boston at the time of the interviews but most of them (had) worked internationally in Europe, the United States, and/or Asia. This international background was chosen to minimize the influence of local habits in the design and material selection approach. 2.1.2. Procedure The interviews were conducted in the architect’s professional environment and lasted between 1 h20 m and 2 h15 m. The interviews were semi-structured. A protocol with open-ended questions about the general concepts and the choice of materials was used as a guideline for the interviews. Typically the interviews started with the question to talk about the project and its general concepts. Later on, the prompts and questions focused more on the materials applied in the project. ‘Why did you choose for this particular material X?’, ‘What issues did you consider when choosing

this material?, ‘How would the use of material Y have changed the project?’, ‘What alternative materials were considered along the process, and why?’, . . . 2.1.3. Data analysis The analysis of in-depth interviews requires a long, iterative approach of identifying key themes, developing a coding scheme, grouping ideas, and finally reducing and structuring the results into a workable report [31]. Following the principles of grounded theory, the coding largely emerged from the data. Units of qualitative data were coded and grouped into themes that characterize the material selection considerations [32]. 2.2. Results The interview extracts showed that the different considerations made before choosing and specifying a material for a project can be very complex and diverse. A wide range of attributes are used to describe materials and several contextual, cultural, or functional thoughts help choosing materials or defining the final character of the space or a building element. Based on the analysis of the interviews, five primary categories of material considerations could be identified to describe the aspects that are at play when selecting and applying materials: (a) Material behavior, (b) Experience, (c) Application, (d) Manufacturing process, and (e) Context. These results are only the first iteration towards an integrated description of materials selection considerations (Section 5) and are therefore not discussed in further detail. A brief description of the suggested categories and subcategories is provided in Table 1. Further information and several examples from the interviews can be found in a study analyzing architects’ material vocabulary based on the interviews [32]. 3. Second study: Focus group interview A second study was conducted to investigate how architects organize the aspects they consider during their material selection process for an architectural design project. A focus group interview brings together ideas of different architects without the influence of the researcher, and allowed us to compare the participants’ unbiased ideas to the findings of the first study. 3.1. Method 3.1.1. Participants Five Belgian architects, three male and two female, between 23 and 46 years of age (average age 39), participated in the group discussion. All of them worked in practice and their professional experience varied between 6 months and 20 years, with an average of 15 years. 3.1.2. Procedure A pilot study was conducted with two architects to verify the setup and interview procedure, and to make small adjustments to the design of the study where necessary. The focus group study consisted of three phases. First, participants were asked to individually list the aspects they consider while selecting a material for a project. Words were written down for 20 min on separate post-it notes (see Fig. 1). Each participant read out their aspects to the others and they were given the opportunity to add extra aspects if they were not already mentioned by the others. Then, the respondents were requested to collaboratively perform a free classification task, categorize all notes and ascribe matching headings. They were invited to organize the aspects into

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Table 1 Categorization of material selection considerations originating from the interview data, including a brief description of the different groups. Categories

Description

(a) Material behavior

 Physical  Sensory

Materials selection considerations are made concerning the physical behavior of materials in terms of structural, electrical, chemical properties and the like. Also the sensory behavior of materials, relating to the stimulation of the different senses (vision, touch, audition, taste and smell), influences the material choice

(b) Experience

 Perception  Association  Emotion

The choice of materials can be guided by the intentions for the project in terms of its atmosphere and experience, considering the interpretation and perception by the users. Associations made with certain materials, or with existing spaces, or the emotion that the architect tries to elicit can also influence the materials selection process

(c) Application

 Function  Use

Functional considerations can be made concerning the function of the space or project where the material will be used, or based on the function of the material itself. Considerations concerning the use relate to the immediate interaction between the material en the user

(d) Manufacturing

 Process  Finishing  Assembly

Considerations are made concerning the possibilities of materials in terms of form and geometry and the techniques used for fabrication. The different finishing techniques of a material facilitate a great variation in appearance or surface properties while keeping the bulk properties and general behavior the same

(e) Context

 Culture  Environment  Time

The context represents a large group of considerations that relate to the larger physical and cultural context of a project. The cultural background of the architect, the user or the client might affect the material selection process. Also the consideration of environmental aspects and other ethics, as well as the direct influence of the physical environment, will guide the intentions of the architect and the choice for materials

3.2. Results

Fig. 1. Jotting down aspects important to the material selection process during the focus group study.

groups in any way that seemed reasonable to them, without any constraints on the number or size of classes. When they reached a classification (after 26 min), they were asked to verify the content of the different groups and make adjustments where necessary. A final categorization was established after about 1 h (Fig. 2). To end, after a short break, the results from the interview study (Section 2) were presented by the researcher and the respondents were asked to discuss their findings compared to the presented categories (Table 1). 3.1.3. Data analysis The results from the study were analyzed at the level of the creation of the groups, using the content of the groups (the actual notes) only as guides to clarify the decisions or the nature of the groups. The actual words listed by the participants were thus only illustrative of the groups and not intended to give a comprehensive overview of the content of these groups. The categories suggested by the focus group based on their free classification task are presented as a result [33].

The focus group created seven different categories of aspects that are considered while selecting a material: (1) Physical aspects, (2) Appearance, (3) Subjective, (4) Cultural context, (5) Physical context, (6) Time, and (7) Money. The layout of the post-it notes with the content of the categories as provided by the focus group participants is represented in Fig. 2. At the end of their discussion, the participants of the focus group presented the results and the content of the categories as follows. The category physical aspects relates to the technical characteristics of materials, which can be found on a technical material data sheet, or are directly related to it (strength, porosity, acoustical parameters, weight). The participants referred to them as ‘‘straight engineering aspects’’. The appearance group covers considerations of the material’s visual or tactual aspects (color, texture, gloss, softness). In the category subjective the material choice was related to intuition and is personally influenced (memory, esthetically pleasing, character, atmosphere). Considerations on quality, style, and expression, were grouped together under the name cultural context. Within this group, a subgroup ethics was created (ecological, durable, availability, re-use). Physical context classes considerations such as location, use, application, and orientation of the building. A separate meaning was attached to the clusters time (adaptability, flexibility, temporality) and money (cost, time of delivery). Even though the participants were not explicitly asked to organize the notes according to the process of the material selection over time, they made an explicit statement for these last two groups as opposed to the others. Time and money aspects were seen as matters that are considered throughout the process, constantly feeding the other decisions. For this reason, time and money were placed crosswise in the focus group’s organization scheme (see groups 6 and 7 in Fig. 2). The comparison of this framework with the categories that emerged from the interview study, resulted in a new proposal to describe the different types of material selection considerations in architecture (Section 5). 4. Third study: Analysis of participatory observations A third study was conducted to refine the findings from the previous studies and present a final categorization of materials selection considerations. Data gathered during participatory observations of an architectural design process were analyzed in

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Fig. 2. Categorization of material selection considerations resulting from the free-sorting task by the focus group participants: (1) physical aspects, (2) appearance, (3) subjective, (4) cultural context, (5) physical context, (6) time, and (7) money.

reference to the categories of material selection considerations identified so far.

4.1. Method One of the drawbacks of conducting interviews (first study) is the risk for selective recall. The interviewees might think they recall why they selected certain materials, but might have forgotten several considerations contributing to a specific material choice. The disadvantage of the focus group study (second study) is that the participants might forget to mention certain important aspects, because the approach is very exploratory and intuitive. Several considerations might only show after careful consideration of several other conceptual considerations. To overcome these disadvantages of the previous studies, the third study made use of data gathered during participatory observations of the design process. During such observations, the researcher joins the design team and participates in all tasks, meetings and activities related to a design project. Following this process from inside, allows taking diary notes about the main decisions taken for the project.

4.1.1. Data Lindekens performed participatory observations of the (re)design process in several firms to study the characteristic aspects of redesign in architectural practice [34,35]. These observations were extensively described in the doctoral thesis of the researcher, which allowed for the data to be used in our study. We analyzed the architects’ material-related considerations during the competition design for the reconversion of a medieval watermill into a new function (Aarschot, Belgium, architects: noA-architecten).

4.1.2. Data analysis Several lines of thought could be formalized for the materials specified for the north wing and west façade of the project. A line of thought represents a logical sequence of thoughts concerning a specific design idea or decision [36]. Even though only considerations concerning the final material decisions were included in the observed data, these lines of thought illustrate why these materials were selected, and thus reflect several considerations made by architects while selecting materials.

4.2. Results The analysis of the different lines of thought illustrated that decisions mostly emerge from contextual considerations, creating a set of preconditions. The materials used in the existing building were, for example, the starting point for the material specifications of the new parts. Even though several traces and scars of changes made over time are visible, the effects of time merge the different pieces into a uniform building block. The architects considered this uniformity an important quality they wanted to maintain in their renovation project and identified ‘uniformity’ as one of the preconditions for the material selection process. Interpreted more freely, these so-called preconditions can also represent the design concept or design intentions. In terms of material aspects, manufacturing, and experiences, different thoughts and considerations clearly influenced each other. In order to achieve a quick unification of the new extensions with the older building, for example, the architects looked for materials that ‘age’ rapidly. Moreover, they wanted to match the color of the red sandstone used in the base of the existing building, which receives its distinct red color from the elements of iron oxide that are contained within the stone. This observation guided the material selection process towards using ferrous materials for the new buildings: ferrous materials assured a matching of colors with the existing materials and would facilitate a fast but controlled aging of the new materials. At certain points the interaction between different considerations thus seems very direct, like for the addition of rust-colored additives to the concrete and the resulting material appearance. For other considerations the interaction is less apparent but rather a reflection made by the architect, like the relation between the experience of unification and the choice for aging materials.

5. Integrated results of the three studies Based on the comparison of the framework suggested by the focus group with the findings from the interview study, and the analysis of the observational data, we present an integrated categorization of the aspects considered by architects while selecting materials for a project (Fig. 3). Below, this categorization is clarified based on examples from the different studies and discussed in

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Fig. 3. Final categorization of material selection considerations, representing the different aspects important to architects while selecting materials in relation to each other.

reference to literature. Major differences between the final categorization and the results from the individual studies are discussed where necessary. Minor differences in terms of terminology are a result of the iterative process and of trying to be as comprehensive as possible in describing the actual content of the groups. Table 2 illustrates the relation between the categorizations resulting from the different studies and the integrated result. 5.1. Material selection considerations in architecture Four categories of material selection considerations are identified: (I) context, (II) manufacturing process, (III) material aspects, and (IV) experience. Each category is divided into different subcategories that describe and organize the considerations more specifically (Table 2). 5.1.1. Context Context is defined as a group of considerations concerning the existing context of the design project: culturally, physically as well as in terms of use. These are all the aspects that are either defined in the design program, or are the existing conditions of the environment the project is situated in. The physical context is defined as aspects concerning the project location (orientation, accessibility) and the immediate environment (adjacent materials and buildings). The physical location usually creates a first set of preconditions for the design choices. The context of use describes the context in which the material is applied (interior/exterior, renovation/newly built) or the function the material will have to accommodate (building’s use, building element). The context of use of a project determines the materialization: a kindergarten, a city hall, or a hospital each require a different kind of materialization. The cultural context includes all considerations that concern cultural values (ethics, style, ecology). Also the interaction between time, money and ethics relates to the culture (see Section 6). In the interview categorization, aspects related to function and use emerged as a separate category; in the focus group categorization, no explicit group referring to function or use was provided (see Table 2). However, an analysis of the content of the post-it notes revealed that aspects, such as ‘user friendliness’, ‘interior/ exterior’ or ‘function of the building’, were included in the physical and cultural context group. Based on the discussion with the focus group and the analysis of the participatory observations, the context of use was therefore included as a subcategory of considerations concerning the context. 5.1.2. Manufacturing process Manufacturing process is defined as a group of considerations that relate to the production process, assembly and finishing technique of materials. The production process tells something about how a material is made or fabricated. Molding, casting, bulk forming, sheet forming, lay-up methods and rapid prototyping are a number of broad

families of production processes that might impact the material considerations [1]. The assembly describes how different elements are installed together. The number of components, ease of assembly, and joining process all influence the manufacture of a building and thus also the material choice. The group finishing process includes all considerations that relate to how a material can be worked. Surface modifications, such as printing, polishing, coating, or texturing, might enhance the thermal, friction, or esthetic qualities while leaving the bulk properties unchanged [1]. Not all finishes can be applied to all materials. The participants of the focus group study did not include manufacturing aspects in their classification. However, during the discussion they argued that manufacturing issues should definitely be included as a separate category of considerations. The fact that manufacturing issues are often considered during later stages of the design process might explain why they were not included in the original focus group’s proposal. 5.1.3. Material aspects The material properties are defined as a group of considerations concerning the tangible aspects or actual measurable properties of a material. These aspects are directly related to the physical behavior of the material and the production technique. A distinction can be made between aspects relating to the technical performance (the technical aspects) and those relating to our senses (the sensory aspects). In order to meet certain performance aspects, architects consider the material’s technical aspects. Technical aspects refer to the different aspects that concern the engineering, like stiffness, strength, porosity, density, thermal absorption coefficient, etc. These properties are organized according to their mechanical, technical, physical, optical, or thermal nature. Sensory aspects are qualities that we experience through our senses. These aspects could thus be organized according to the different senses into visual (color, gloss), tactile (roughness, warmth), and auditory aspects (dampness, pitch). The olfactory aspects are less obvious to be described, even though the smell of a material was mentioned as an aspect that might influence the experience of the final project and thus the choice of materials. Where taste might be of importance in the field of (food) product design, it will have no immediate significance in architecture. The sensory behavior of materials creates a field of opportunities for architects selecting materials. It is largely through these characteristics that architects keep control over what the building will look and feel like and that they will provide an answer to the desired or intended expression and appearance of the project. 5.1.4. Experience Considerations of experience are defined as concerning the perception of the (material) environment by an individual, and referring to the ‘intangible characteristics’ of a material or a project. The choice of materials will largely influence the observer’s experience of a building or room. Results from both the first and second study

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Table 2 Final categorization of material selection considerations in relation to the groups resulting from the focus group and interview study. Final categorization (I) Context

— Physical context — Cultural context

— Context of use

Focus group study

Interview study

(4) (5) (6) (7) -

(e) Context

Physical context Cultural context Time Money

(c) Application

Environment Culture Time Function Use

(II) Manufacturing process

— Production — Assembly — Finishing

-

(d) Manufacturing

Process Assembly Finishing

(III) Material aspects

— Technical aspects — Sensory aspects

(1) Physical aspects (2) Appearance

(a) Material behavior

Physical Sensory

(IV) Experience

— Perception — Association — Emotion

(3) Subjective

(b) Experience

Perception Association Emotion

revealed that architects have trouble discussing aspects related to experience and rather use them intuitively. As no established descriptions exist to distinguish between different types of experiences within an architectural context, the empirical data was compared with some definitions and classifications commonly used in industrial design. As a result, we identified the following types of experiential material considerations: perceptions, associations and emotions. The perceptual aspects, also referred to as expressive meanings [21,22], describe the character and meaning attributed to materials or a space after the initial sensorial input (formal, massive). Architects can consider materials based on their contribution in creating the intended atmosphere or expression. Associative meanings are mainly used for defining certain qualities of materials [22] and are fed by the associations people make with aspects, objects or situations they know by retrieval from memory or past experiences (hospital-like, cheap-looking, Swiss-cabin material). Emotive aspects are personal emotional reactions of the user to the environment (comfortable, repulsive) [14]. The surroundings will affect people’s emotions, and architects might have the intention to move people through their architecture. A particular spatial composition, in combination with specific lighting, and well-chosen materials might evoke certain feelings or personal emotional reactions with its occupants. These reactions differ from person to person and can be influenced by mood, preference and culture. 5.2. Interactions between considerations Both the interview study and the focus group study reveal that even though considerations can be categorized, the boundaries between the different groups are sometimes blurry and several considerations are interrelated. Given our interest in the importance of material experience during the materials selection process, it seems important to describe the relation between the different considerations. 5.2.1. Context as set of preconditions A distinction can be made between considerations that relate to a specific material decision and considerations that concern the set of preconditions for selection. In this matter, the reflections concerning the context are different from the others: they are defined by the project situation, and thus correspond to the aspects taken into account by the architect while taking material decisions. Contextual considerations will mostly influence or guide other considerations and further decisions. A one-way interaction can be defined between aspects from the context group (physical, use, or cultural) and the other groups. This relationship is represented in Fig. 3 by a one-way arrow. Examples retrieved from the

interviews show that, even though the context is a given, each designer will select other aspects from that context to guide or verify the material decisions. One of the participants of the focus group, for example, mentions that when building in the woods [physical context], the construction site might be difficult to access by truck. For practical reasons, this precondition might exclude the possibility of casting concrete on site from the design options [manufacturing]. Other contextual aspects can be rather prescriptive, like the consideration of building regulation codes in certain countries or regions. In general, the preconditions help, guide and limit the designer while taking decisions. 5.2.2. Interactions between decisions One of the architects of the focus group discussion argues that one cannot dictate a material to a building. He continues that the building ‘‘demands its own material, from a certain logic, and from a set of preconditions, which can be contextual but also emerge from the design. And it is together that they receive their meaning’’. This illustrates the importance of the contextual preconditions in guiding the design process. Nevertheless it also introduces the impact of ‘‘a certain logic’’ or a set of preconditions emerging from the design itself. The in-depth interviews reveal that during the search for a material, all four categories will have to be thought over before taking a final decision on a material. One interviewee brings up that a material decision is never taken for one reason only. He argues that when ‘‘you find a minimum of three reasons for something you have a sure-proof alibi’’. An internal interaction exists between the different considerations the designer has to take decisions in (see dotted arrow in Fig. 3). Moreover, decisions taken for one aspect impact the options left for the other aspects. For example, when considering a desired project experience, the architect will draw on specific materials or material aspects to create this experience. When looking for a formal expression [experience], the architect might want to work with glossy and even materials [material aspects]. These material aspects in turn require specific manufacturing techniques in order to be achieved. A concrete surface could, for example, be polished to make it shine [manufacturing]. 6. Discussion 6.1. Material selection considerations for architects The categories of considerations identified in this study correspond closely to what is described in the international literature in architecture [1,29]. Some small differences can be found in the configuration of the groups, or whether a group is defined as a main element or a subgroup, but overall a lot of similarities exist.

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The technical performance criterion in Hegger’s model [29], for example, includes the manufacturing issues as well as the technical behavior of the materials, and the perception criterion covers both sensory and experiential issues. In this study, manufacturing issues are formulated as a distinct consideration. Sensory aspects of a material are separated from the experience and fit with the material aspects. Even though architects seem to make a clear distinction between the physical aspects and the appearance of a material, these aspects were grouped together under material aspects to emphasize that they all directly relate to the behavior of the materials themselves. This implies that they are materialinherent and thus could be described objectively in relation to the material. Currently architects have to consult different sources to receive information on these aspects: technical data sheets in combination with material samples. The most apparent difference between our findings and other models concerns the context considerations. In literature, these contextual considerations appear to be limited to ecological and economic aspects. Whereas ecology/green design and cost are hot items in the current building scene, there are far more societal, cultural, and environmental issues that affect the material selection process. Our results show that the importance of cultural and physical context aspects cannot be ignored during the selection process and thus should be explicitly mentioned when creating categories of material selection considerations. A building is embedded within an existing physical and cultural context, which cannot and should not be ignored. The different locations of the studies (Boston, Brussels) provided insights in some minor differences that exist in the material selection process because of the project locations and architects’ background. For example, the interviews showed that building codes form a major decision factor for choosing materials in the United States. This consideration can, however, be embedded as an aspect of the cultural context influencing the design decisions. During the focus group discussion, participants also argued that the cultural context can largely influence the considerations taken: when building in third world countries, or rebuilding houses after a major natural disaster, the major consideration will be to have a roof above one’s head. In this sense, the impact of different local influences or the importance of certain aspects compared to others, can be included in contextual considerations. It is obvious that different emphases will be laid depending on the (cultural) context. Comparing the responses form the US architects with those from the Belgian architects, however, suggests that several differences can be accounted for in the approach to and importance attached to the different categories presented here. Hegger includes economical aspects as a separate element in his model [29]. Our results confirm that considerations concerning the cost will definitely impact the material choice. We argue, however, that the cost is an aspect that will loose or gain importance depending on the cultural and social context of the project. Therefore economical considerations should be included as part of the context as well. This corresponds to the note made by van Kesteren that an aspect such as cost provides the boundaries of a design [27]. Design considerations on materials can then take place within these boundaries. In this view, Rowe argues that the development of a design is strongly influenced by the situation of the design problem and the situation of the designer [37]. The situation of the design problem refers to what we define as context. The influence of the situation of the designer can be interpreted as a third dimension to the categories presented. After all, the personal approach of the designer will determine how the considerations will be interpreted and used, rather than alter it. It is not the type of considerations that will change, but only the meaning attached to them.

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The research was based on three specific tracks of empirical research in order to include as many aspects relevant to the material selection process as possible. The categories of material selection considerations form a useful description of the aspects important to architects while choosing materials throughout the design process, but are based on a limited number of data sources. The analysis of a larger number of material selection processes within varying situations (culture, building function, location, etc.) would be desirable to validate the different categories and present them as a comprehensive model of material selection considerations in architecture. In further research, it would be interesting to verify how different considerations loose or gain importance over the course of the design and material selection process. 6.2. Architects and industrial designers selecting materials Aspects concerning material aspects, manufacturing, and experience are also considered during the materials selection process in industrial design [27,28]. Besides this, in industrial design, the function and use of a product will gain a prominent place in taking materials decisions [28]. In architecture, the function or use of a building or space seems to be considered less explicit when selecting materials. Moreover, industrial designers explicitly consider a product’s shape [28]. Materials are shaped into a certain geometry in architecture as well, but most of the time this geometry confines itself to standard building elements such as walls or floors. The geometry of a building element is rather related to the function, or specific manufacturing issues. In terms of interactions between different considerations, and the influence of the context, Pedgley describes that designers are responsible for identifying, initiating, and synthesizing the various stakeholder influences on material and manufacturing decisions in industrial design [38]. Each of these stakeholders frame certain preconditions for the material selection process and can be responded to in terms of specific manufacturing techniques, specific material behavior, or intended material experiences. This appears very similar to the interactions we found within architecture: the architect identifies and sets the practical constrains based on considerations of the context (including cultural and economical issues), which influence the decisions taken in terms of manufacturing, material behavior, and experience. It seems that several correspondences can be found between the material selection process in architecture and industrial design, and that it are mainly the set of contextual preconditions that will be different for the two disciplines. 6.3. Importance of experience aspects The discussion with the focus group revealed that experience aspects feel intuitive to architects: at the beginning of the discussion, these grouped aspects were named ‘gut feelings’, or ‘intuition’; later on, the name was changed to ‘subjective’. Moreover, both the interview and focus group study revealed that architects have trouble to identify or name these ‘subjective’ experience aspects. One of the participants mentioned that ‘hard’ can relate to the different associations people make, and that each architect would compose a different palette of materials when they would be asked to design a ‘hard volume’. Aluminum cladding might not be very hard in technical terms, but it might feel or seem hard depending on how it is applied. As little research on material experience has been conducted within architecture, we relied on definitions and descriptions from the field of industrial design to gain a better understanding of the intangible aspects of materials important to architects. In general, these definitions proved to be useful to describe the different aspects of experience considered by architects. Aspects related to perceptions, association and emotions were

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found to be important to the architect during the design process. The results hereby confirm the importance of materials’ experience aspects in architecture and reveal that the shift from a technically oriented material selection process to a more experience-centered selection of materials is not limited to the discipline of industrial design. This growing interest in material experiences in different design disciplines, and the lack of experience related vocabulary and descriptions in architecture, confirm the need for more systematic descriptions and information on material experience. Karana argues that the meaning of a material ‘‘is evoked by the interactions between product aspects (such as shape and function) and material properties, with respect to how and in which context the material is used and who the user is’’ [26]. Several parallels can be drawn between Karana’s Meaning of Materials model and the categories and interactions presented in this study. In our description, we see that experiences are interrelated with the material aspects and manufacturing techniques, while being influenced by the context. In Karana’s model, the user forms an important additional parameter influencing the meaning of a material: in order to determine or describe the meaning of a material, the specifics of the user (gender, age, culture, etc.) should be considered [26]. As a building is usually not designed for a single type of user, the story might be slightly different in architecture. Most buildings will be used by a number of people with varying ages, gender, and backgrounds. This implies that architects usually have to design their buildings for a mix of users. Whereas the consideration of an explicit user seems to be very natural in industrial design, this consideration is less obvious in architecture. Nevertheless, as experience concerns the effects generated by the interactions between a user and a product [16] (or material), it seems necessary to consider the user more explicitly when researching material experience in architecture. For this study, it was not our intention to scrutinize the differences between architecture and industrial design. A more thorough investigation of these differences, especially in terms of userinteraction, is however, desirable to describe more nuanced and architecture-specific categories and develop a better understanding of experience in architecture. Further research will focus on the specificities of (material) experience in architecture by considering the interaction between users and building materials.

7. Conclusions This paper illustrated that architects identify and set the practical constrains for materials selection based on considerations of the context, which influence the decisions taken in terms of manufacturing, material behavior, and experience. In investigating architects’ materials selection considerations, the study revealed a shift from a technically oriented material selection process to a more experience-centered selection of materials. Aspects related to perceptions, associations and emotions were found to be important to the architect during the design process but are addressed rather intuitively and often difficult to identify or name. This growing interest in material experiences, and the lack of experience related vocabulary and descriptions in architecture, confirm the need for more systematic descriptions and information on material experience. Furthermore, the study showed that several correspondences can be found between the material selection process in architecture and industrial design and that mainly the set of contextual preconditions will be different for the two disciplines. More specifically, the descriptions of material experience used in industrial design were found to be relevant in an architectural context and can provide a first step towards offering more systematic knowledge and information on material experience to architects.

Acknowledgements The research reported in this paper was conducted in the context of Lisa Wastiels’ PhD research at the department of Architectural Engineering of the VUB, funded by the Research Foundation – Flanders (FWO). Her current research received funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No. 201673. The authors thank the architects that participated in the interviews and focus group study, and are grateful to Jonas Lindekens for the data provided for the third study. They also express gratitude to Hendrik Schifferstein, whose insightful discussions on product experience greatly contributed to the research. References [1] Ashby MF, Johnson K. Materials and design: the art and science of material selection in product design. Oxford: Butterworth-Heinemann; 2002. [2] Hegger M, Fuchs M, Zeumer M. Appropriate forms of construction – criteria for the selection of materials. Detail 2006;2006(6):652–7. [3] Fernandez J. Material architecture: emergent materials for innovative buildings and ecological construction. Amsterdam: Architectural Press; 2006. [4] Malnar JM, Vodvarka F. Sensory design. Minneapolis: University of Minnesota Press; 2004. [5] Pallasmaa J. The eyes of the skin. Architecture and the senses. London: WileyAcademy; 2005. [6] Material ConneXion [Internet]. A global materials consultancy and library of innovative and sustainable materials; 1997. [cited 15.05.10]. [7] Materia [Internet]. Materialize the future; 1998. [cited 15.05.10]. [8] MatériO [Internet]. Independent information centre on materials and innovative products; 2001. [cited 15.05.10]. [9] Beylerian GM, Caniato M, Dent A, Quinn B. Ultra materials: how materials innovation is changing the world. London: Thames & Hudson; 2007. [10] Keuning D, Melet E, Kruit C, Peterse K, Vollaard P, de Vries T, et al. Skins for buildings: the architect’s materials sample book. Berkeley, CA: Gingko Press; 2004. [11] Lefteri C. Materials for inspirational design. Mies: RotoVision; 2007. [12] Mori T. Immaterial/ultramaterial: architecture, design, and materials. New York: George Braziller; 2002. [13] Schifferstein HNJ, Hekkert P, editors. Product experience. Oxford, Amsterdam: Elsevier Science; 2008. [14] Desmet PMA, Hekkert P. Framework of product experience. Int J Des 2007;1(1):57–66. [15] Desmet PMA. A multilayered model of product emotions. Des J 2003;6(2): 4–13. [16] Hekkert P. Design aesthetics: principles of pleasure in design. Psychol Sci 2006;48:157–72. [17] Schifferstein HNJ, Cleiren MPHD. Capturing product experiences: a splitmodality approach. Acta Psychol 2005;118:293–318. [18] Fenko A, Schifferstein HNJ, Hekkert P. Looking hot or feeling hot: what determines the product experience of warmth? Mater Des 2010;31(3): 1325–31. [19] van Kesteren IEH. Product designers’ information needs in materials selection. Mater Des 2008;29(1):133–45. [20] Karana E, Hekkert P, Kandachar PV. Material considerations in product design: a survey on the crucial aspects used by product designers. Mater Des 2008;29(6):1081–9. [21] Karana E, van Kesteren IEH. Material effects: the role of materials in people’s product evaluations. In: Karlsson MA, Desmet PMA, Erps J, editors. Proceedings of the 5th international conference on design and emotion. Goteburg, Sweden; 2006. [22] Karana E, Hekkert P, Kandachar PV. Meanings of materials through sensorial properties and manufacturing processes. Mater Des 2009;30(7):2778–84. [23] Ashby MF. Materials selection in mechanical design. 2nd ed. Oxford: Butterworth-Heinemann; 1999. [24] Mangonon PL. The principles of material selection for engineering design. New Jersey: Prentice-Hall; 1999. [25] Addington MD, Schodek DL. Smart materials and technologies: for the architecture and design professions. Oxford: Architectural Press; 2005. [26] Karana E, Hekkert P, Kandachar PV. A tool for meaning driven materials selection. Mater Des 2010;31(6):2932–41. [27] van Kesteren IEH, Stappers PJ, Kandachar PV. Representing product personality in relation to materials in a product design problem. In: Mazé R, editor. Proceedings of the 1st Nordic design research conference. Copenhagen, Denmark; 2005. [28] van Kesteren IEH. Selecting materials in product design [Doctoral dissertation]. Delft: TU Delft; 2008. [29] Hegger M, Drexler H, Zeumer M. Basics Materials. Basel: Birkhäuser; 2007.

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