3.1. The architectural design process

Although shape grammar was used to produce the transformation, there are several ways of managing the architectural rehabilitation process. The traditional architectural process of planning and designing rehabilitation work relies on the architect's knowledge and proceeds by exploration, using the project program, the existing building, and their combined constraints. To these elements, architects add the human capacity of continuous adaptation and the ability to return repeatedly to the beginning of the process.

This research on design by shape grammars explores a method that seeks to encode both the architect's knowledge and the knowledge acquired from other experiences of rehabilitation work in the form of rules. These rules are used to transform dwellings, and incorporate substance and knowledge, and are assumed to represent the architect's knowledge from a wider perspective. However, although vast, the grammar knowledge itself is limited to the data entered into the knowledge database.

3.2. Implementation of the transformation grammar

At later stages and in more complex grammars, the computerized implementation of a shape grammar is beneficial because it allows a greater amount and variation of designs that will be generated in less time.

Experimental subjects who manually applied Duarte's (Reference Duarte2001) shape rules of the Malagueira grammar to develop a design solution revealed that a grammar written for the computer is difficult and slow for a human designer to understand and apply (Duarte, Reference Duarte2001). This indicates that, in an earlier phase a shape grammar should be written so that it can be easily understood and applied by human designers. This will allow the grammar to be validated and possibly implemented on the computer afterward.

The mechanism used to generate solutions based on the transformation grammar is to a certain extent similar to an expert system because it uses the knowledge of an expert to the problem field and, by using a particular methodology, provides a solution.

Expert systems are used to simulate intelligent human processes for gathering, planning, rationalizing, and representing knowledge, and to reproduce this in the form of computer-based representations. The aim of creating an expert system is to produce, by rationalization and logical proposals, a representation of knowledge, demand, reasoning, and problem solving. From this perspective, an expert system lies at the core of the transformation grammar. The transformation grammar is similar to a spatial and formal expert system because instead of just codifying the expert knowledge in rules using symbols, the transformation grammar also uses shapes.

The aim of using the transformation grammar model is to generate transformations based on a language composed of rules derived from the intervention criteria for the existing housing spaces defined by experts, as in an expert system.

The transformation grammar has a conditional part in addition to a shape part, which covers knowledge in terms of the dimensions and the functionality of the dwelling areas. This conditional part was developed by using natural language (IF/Then conditions or tables and charts) at a first stage and later by using a mathematical language that forms a descriptive grammar. These descriptions reveal certain characteristics that cannot be described in shapes.

As in an expert system, in its initial stage the knowledge contained in the conditional part of the rules could be informed by trees, flow diagrams, and/or decision-making tables, and operated manually. In this study, the first phase of systematizing the transformation principles and rules was carried out using tables, flow diagrams, and text, and certain descriptive rules were produced to assess feasibility.

On a more efficient level, the transformation grammar may be computerized and, in this case, will consist of a program that processes the data to generate a more rapid solution to a given problem.

Research into computerized grammar interpreters has developed substantially in recent years, but a great deal of ground still needs to be covered in order “to make an impact on industry methods using grammar based approaches” (Chase, Reference Chase2010). The goal of creating a shape grammar interpreter is to make conceptual design tools that support designers’ ways of thinking and working and enhance creativity (e.g., by offering design alternatives that would be difficult or impossible to produce without the use of such tools; Chase, Reference Chase2010). According to Tapia (Reference Tapia1999), it should be easier to use a program to try out shape grammars than it is to test them by hand.

4.1. Families/future inhabitants

We used five families, differently composed in term of numbers, age, and family relationships, namely, couples with children, young couples without children, old couples, and couples with children from previous marriages. Interviews were done with five families, which were then assigned to different design problems (Table 1).

Table 1. Example of the results from the interviews with Family 01

Initially, people living alone were not considered because the sample dwellings were too big for this family type. Later, the study focused on how couples with no children or one-person households could be accommodated by dividing each dwelling into two autonomous smaller dwellings, because this accounts for one of the most sought-after types of accommodation in the rehabilitation market in Lisbon (Caria, Reference Caria2004). The division of dwellings was studied, and some rules for the implementation of this strategy were also designed. Nevertheless, the transformation grammar does not include this rehabilitation strategy.

4.2. Housing functional program

The minimum functional program for each family was determined in accordance with Pedro's (Reference Pedro2000) guidelines and then combined with the requirements expressed by each family in an interview especially designed for this purpose (Table 2). Families were presented with what would be the minimum functional program assigned according to the number of inhabitants and their relationships within the family. In the interviews, the families were asked to describe the dwelling they thought they needed (i.e., not an ideal dwelling but one that could fulfill their real needs). They also were told that the dwelling would be in a rehabilitated building with small rooms (the average area of the habitable rooms is 13 m²) and that they would have to consider economic constraints. The description had to include the required housing functions or rooms, as well as the topological relations between them. Finally, they were asked to rank their requirements in order of priority.

Table 2. Calculations for the net floor area (m²) for each family based on the minimum values in the functional program and the needs expressed by each family

Note: The lightface italic values indicate not being part of the minimum functional program but requested by the family. The bold roman values indicate adequate floor area, and the bold italic values indicate excess floor area.

^aThe additional media room area was not considered, because the living room area was indicated by the residents.

^bThe circulation area was calculated using the ratio resulting from the case study analysis (16%).

4.3. Existing houses

The housing sample is composed of 25 dwellings, some of which were chosen for use in the first and second steps. The selection criterion for the first and second steps was to choose 10 dwellings of varying types and areas that could potentially satisfy the requirements of the functional programs for the selected families. To verify this criterion, the area of each dwelling was compared with the area requirements of each family (Table 3).

Table 3. Correspondence between selected dwellings and family size in the first and second steps

Note: CT, compatible types; NC, not compatible, that is, types unsuitable for the size of the family. These dwellings may correspond to the functional program if divided into two different dwellings.

Two different dwellings that satisfied this criterion were then assigned to each family to obtain 10 different dwelling proposals at the end of the experiment (5 families × 2 dwellings; Fig. 2). The 10 chosen dwellings corresponded to 3 Type A dwellings, 2 Type B dwellings, 2 Type C dwellings, and 3 Type D dwellings (Fig. 3).

Fig. 2. Dwellings selected for the first and second steps.

Fig. 3. Subtypes of rabo-de-bacalhau dwellings.

Rabo-de-bacalhau dwellings were categorized into four subtypes in accordance with characteristics common to all the cases in the studied sample. The type (Fig. 3, left) has characteristics that are common to all subtypes: two symmetrical dwellings per floor, a front wing with a façade overlooking the road that contains most of the rooms and is occupied exclusively by the social and private areas; a rear wing in the rear façade with the service areas; and a main access nucleus in the center of the building. The principal characteristics used to distinguish between the four subtypes were width of front wing, as well as depth and function use of rear wing (Fig. 3).

For the third step, three different dwellings were chosen that were not used in the first and second steps. As stated above, the case study dwellings are characterized by small social areas. It was therefore established that the social areas (living room, dining room, and home office) should occupy at least two rooms or not less than 18 m² (depending on the number of inhabitants). Thus, a dwelling (e.g., for a couple with two children) would require at least four inhabitable rooms (two bedrooms plus two social rooms). The different characteristics of the subtypes cause different rehabilitation strategies that were defined in the transformation grammar.

4.4. Pack of ICAT functions

In the design exercises, ICAT pack was reduced to technologies that had an impact on spatial organization. The resulting requirements were then added to the functional program.

The technologies and space requirements considered were the following:

• • home cinema or large TV screen, which require a spacious living room with a distance of at least 3 m between the screen and the couch or chairs;

• • home office, isolated or integrated into another area such as the living room, according to the needs of the new dwellers; and

• • definition of independent night and day areas for sector alarms.

4.5. Step 1

The first and second steps aim to identify the fundamental functional, spatial, and constructional transformations to be carried out on the dwellings that were studied. The first step, performed by the main author of the research, consisted of a design process to adapt the dwellings. This step was done in order to infer some basic transformation rules and to test the feasibility of the exercise, before assigning it to other subjects in Steps 2 and 3.

This step included two stages. The first stage consisted of proposing transformations to the dwellings taking the future dwellers’ requirements and constructional constraints into account. This resulted in 20 different layout proposals, 2 for each family/dwelling pair, in order to explore the various possible solutions. The plans corresponded to possible solutions for the transformations that fulfilled most of the requirements in accordance with the constructional restrictions of the building. The procedures required to perform this experiment included use of data concerning the family, the functional program, and the dwelling, design rehabilitation solutions on tracing paper, and the subsequent use of CAD for verification purposes (e.g., net areas and extent of demolition).

The second stage consisted of inferring transformation rules from the transformations proposed in the first stage. Only higher level transformation rules were inferred, meaning that detailing rules were not considered.

The rules were inferred by text, then by drawings. All the transformations regardless of the implementation sequences were written from all the generated designs. Subsequently, these transformations were drawn, step by step, in order to simulate a possible sequence of actions.

Space syntax was also used to help clarify the transformation principles, according to adjacency and connectivity issues, and make them more simple and rational. To this end, a transformation sequence was produced using both the floor plan and the graph (Fig. 4). Figure 4 also shows the shape rule used in each step of the derivation. The results revealed that not every shape action has an immediate corresponding graph action. In the fifth step of the derivation in Figure 4, a change in shape (i.e., the enlargement of a room) did not have an impact on the justified graph. Nevertheless, changes in the graph are usually linked to changes in the shape and function of a room in terms of the dwelling layout. Changes in arcs and nodes in the dwelling graph occurred as a result of changes in door positions, the size of openings, connections between rooms, division of rooms, or the addition of different rooms within a single space. During this stage, we understood that adjacency graphs and not just connectivity graphs (as the ones shown in Fig. 4) would be extremely useful to inform transformation decision as such as demolitions.

Fig. 4. The derivation of a rehabilitated dwelling: sequences of rehabilitation decisions made through changes in layout, application of shape rules (first draft of rules), and graph transformation.

The conclusion of first step enabled the following to be accomplished:

• • After the first transformation, all others followed substantially the same criteria.

• • When the functional program requested two or more bedrooms, the first decision was the location of the private area.

• • When the functional program requested fewer than two bedrooms, the first decision was the location of the social area.

• • Transformation rules differed according to different dwelling types.

4.6. Step 2

In Step 2 architects with experience in designing houses were used to design more rehabilitation solutions. The goal of this step was to enlarge the set of rehabilitation solutions in order to understand how different approaches may be used to solve the same problem and, therefore, to obtain a larger basis for inferring rules. Another goal was to understand how designers think when they are designing, if it is possible to encode that process into design rules, and how to do it. To accomplish these goal and to enable the design of the most accurate solution for the given problem, we proposed to put designers “into the mode of doing” as Schon suggests (Reference Schon1992, p. 131). This design step aimed to identify the functional, spatial, and constructive transformations performed by human designers by hand, in order to infer the corresponding transformation rules and encode them into a transformation grammar.

In this second step, the same data from Step 1 was used, namely, 10 existing dwellings and five different families. Two of the architects participating were asked to design a solution for all 10 family/dwelling pairs (2 dwellings for each family), which yielded 20 different drawn proposals. Three architects designed for five family/dwelling pairs (1 dwelling only per family), producing 15 different drawn proposals.

The design tasks were explained to each of the architects separately, and they then completed the work in their offices. In addition to a verbal explanation, the other elements given to the designers were the dwelling layouts (plotted on a scale of 1:100, or DWG drawing), a written description of family desires, and a brief description of the major functional and constructional aspects they had to follow.

The architects were asked to perform two tasks: first, to draw a design solution for each family/dwelling pair, taking the functional program into account as well as the construction constraints; and second, to explain the strategy they used to obtain each design proposal.

The data that resulted from this step included sketches (two of the architects designed by computer and therefore did not produce sketches; Fig. 5), final drawings of the proposed layouts, and verbal explanations or texts explaining the process followed in each case.

Fig. 5. Drawings produced by architects during Step 2.

Figure 5 shows total and partial solutions of dwelling transformations that correspond to the traditional process of architectural designing going from the general to detail and back again. These drawings and the explanations, despite being vague, help us to “tell the story” of the design process and then, after identifying a possible sequence of actions, abstract the shape aspects of the dwelling layouts proposals and divide transformations acts into “erasing” (demolishing), “adding” (constructing), and assigning (functions to rooms).

The data was analyzed, and transformation rules were inferred. It was possible to identify two types of design proposals: only one architect proposed transformations where the kitchen moves to the front façade (Fig. 6a), and four architects proposed transformations where the kitchen is left in its original position in the back wing (Fig. 6b–d). A third transformation method, which enabled the architects too divide the dwelling into two autonomous ones, was proposed in a later stage (Fig. 6e). All the architects respected the given constraints and the priorities expressed by the families. One architect did not comply with the constraint of not demolishing more than 2 m of wall. In general, they said that it was difficult to respond to the functional requirements because of the original morphology of the dwellings and the demolition constraints.

Fig. 6. An example of the results of Step 2: original dwelling and transformations performed by four architects.

The solutions proposed by the architects were evaluated in order to calculate the level of satisfaction of the dwellers and the fulfillment of the functional and constructive rules. The following criteria were used in the evaluation: satisfaction of functional program; satisfaction of the extra areas requested by families and the connections between them; satisfaction of the general functional aspects for housing; and satisfaction of constructional aspects in accordance with rabo-de-bacalhau buildings. The highest level of satisfaction was obtained when the proposal fulfilled most of those aspects (Fig. 7). The evaluation enabled the different project options to be selected and the reasons why one option was more successful than the others to be understood. In the examples of Figure 6, the solution 6a got the highest evaluation because by moving the kitchen to the front façade, the solution allows private areas to be individualized, and social and service areas to be together and near the entrance. Solution 6b got ranked second in the evaluation because the social areas were moved to the back wing near the original kitchen instead of moving the kitchen.

Fig. 7. An example of a functional evaluation of one of the adapted dwellings (the one that got the highest evaluation).

The general opinion expressed by the architects was that the rules were the following:

1. 1. Difficult to respond to in functional terms because of the original morphology of the dwelling. It was difficult to ensure that the private area was kept intact while also keeping the social area together and close to kitchen.

2. 2. Very restrictive in constructional terms, owing to demolition restraints. In most cases, the rule of not demolishing more than 2 m of wall was a huge restriction. This rule restrains actions such as merging different areas to create larger ones, and the incorporation of circulation areas within social areas.

The result of this step was a transformation grammar that can be used to adapt existing dwellings to specific families.

4.7. Step 3

The third step was carried out by a class of 22 architecture students on the “Shape Grammar and Digital Tools” course from the third year of the Integrated Masters in Architecture program at the Instituto Universitário de Lisboa. The students had had previous classes on the subject of shape grammar, so they were familiar to some extent with the mechanics of using rules and shapes.

The goal was to test the proposed grammar on dwellings that had not been used to infer its rules. This enabled us to check whether the inferred rules provided the compositional means for making new transformations in other existing dwellings for other families. The exercise was explained by the author to all the students at the same time, and the work was subsequently completed in the presence of the author. The author explained the aim of the exercise, the tasks, how they had to be executed, and how to use the grammar and the rules.

Students were divided into 10 different groups, consisting of one, two, or three people (Table 4). The aim of putting students into groups of different sizes was to test different approaches to using the grammar. The approaches examined were attempts to use the grammar by one person only and attempts involving two or three people, thus allowing for dialogue and exchange of ideas.

Table 4. Composition of groups in the third step

^aDid not complete the experiment and did not comply with all of the rules.

^bCompleted the experiment but did not comply with all of the rules.

^cCompleted the experiment and complied with all of the rules.

This first session lasted 3 h, during which only five groups were able to finish one dwelling derivation. Three of the remaining five groups took part in a second 2-h session in order to finish the dwelling derivation. The groups worked in a computer room, each using one computer equipped with Autocad software.

The groups worked with five dwellings that were part of the corpus but had not been used in previous steps. The five family profiles used in Step 2 were also used in this step. Each of the 10 student groups had to transform one dwelling for a family.

In addition to a verbal explanation, the following additional information was given to each group:

• • the adapted functional program (the ideal program plus the description of the family's extra requirements, in order of priority), including the net floor areas required for each room;

• • the dwelling layout in a DWG file; and

• • a version of the transformation grammar rules in which the function and dimension conditions were simplified in natural language in Portuguese (81 rules grouped according to a specific sequence).

The dwelling transformations obeyed the following task sequence:

1. 1. The author of the research started by explaining the grammar, the sequence of rules (Eloy & Duarte, Reference Eloy and Duarte2012a), and the aim of the exercise.

2. 2. Students had to read the family's adapted functional program. This functional program had a description of the spaces required and the topological relationships, as well as the net floor area required.

3. 3. One dwelling, previously chosen by the author (in accordance with predefined data), was given to students as a DWG file. The initial labels hs, nhs, Xki, Xba, Xla, and Cbc were already marked on the dwelling layout. In addition to the floor plan, the DWG file included a grid in which the new dwelling layout had to be entered, step by step, after each rule application.

4. 4. Students then started the dwelling transformation, using the given functional program and the shape rules document.

5. 5. Students drew onto the DWG file. Each new rule applied had to be written in the file and the resulting application drawn. They were asked not to delete anything and to change to a new color grid if they made a mistake or chose another approach to the design (as explained in sequence 3 above).

This exercise allowed the behavior of students to be observed in terms of the way they approached the application of the grammar.

The final layouts obtained from this exercise were as follows, by student's group (see Fig. 8). Three patterns of design emerged for the approach to the problem of rehabilitation:

• • Some students first analyzed the entire dwelling and tried to mentally simulate the final result before starting to apply the rules. This occurred with students who were organized in groups. These groups began the transformation by analyzing the architectural features of the dwelling.

• • Some students began by applying the shape rules without first analyzing the entire dwelling. Some of these cases produced valid results. In other cases, the sequence of rules was applied incorrectly and the final result was impaired (e.g., bedrooms became too small or walls were added too close to other walls). One instance of this situation occurred when the application of rules was initiated by assigning private areas rather than social areas.

• • Some students applied the rules correctly, in the right sequence, and because they had anticipated each step, their derivation never produced conflicting results.

Fig. 8. The final dwelling layouts at the end of the exercise by student's groups. f, Family; d, dwelling; es, students.

The following conclusions could be drawn from this exercise, each of the conclusions that implied alteration to the grammar were performed:

• • Contrary to what happened in the second step, the demolition restrictions were not considered a problem in transforming the dwelling, except in one case involving one group derivation. This happened because students understood from the beginning that the goal was to use the grammar and not to give their personal answer to the design problem.

• • The major difficulty was finding rooms that met the net floor area conditions. Almost all the rooms were smaller than the areas requested. This obstacle led to some possible solutions that were later integrated into the rules:

  • • assigning a tolerance to the requested area (e.g., 10%; F ≥ 9 m² means that F ≥ 8.1 m²),

  • • allowing a room (e.g., a double bedroom) to be allocated to a smaller space if the floor area could be enlarged,

  • • allowing a space to first be enlarged and then assigned a function,

  • • using the areas required for the minimum level, even if the recommended level had been chosen by the family.

• • Instead of having different changing shape rules for each of the functional areas, it was preferable to have a group of changing shape rules with the shape part equal and the conditions differing according to functional or dimensional restrictions.

• • Because there are mandatory rooms (those required by the functional program) and optional rooms (the extra ones required by the family, in order of priority) and it is sometimes not possible to satisfy all requirements, it would be better to assign in the following order:

  • • First, allocate and ensure the mandatory rooms;

  • • Second, allocate the optional rooms.

  Although this option is an interesting possibility, its application would solve some problems but also create others. The main new problem would be the difficulty in keeping the rooms in the different functional areas together, given that they would be attributed at different stages.

The layouts obtained from this step were as follows, by students group (see Fig. 8):

• • Groups 01 (8a), 04 (8d), 07 (8 g), 09 (8j), and 10 (8 k) failed to obey some shape rules during the derivation (e.g., dimension conditions, new demolition types, or wrong sequence of rules). Most of these are groups of three students used the process of discussing the right solutions rather than applying directly the grammar. Their final plan contained misinterpretations and showed that mixing intuition on the design with the grammar is not a good choice at this phase of design because the grammar framework is not completely followed and therefore the final solutions reaches dead ends or incomplete layouts.

• • Groups 02 (8b), 03 (8c), 06 (8f), and 08 (8i) obeyed all the shape rules and explored a viable and correct dwelling layout in accordance with the transformation grammar. These groups had one or two students who immediately tried to apply the rules as we asked. The final results were positive.

• • Group 05 (8e) did not obey one fundamental shape rule considering the assignment of the private bathroom, and the dwelling layout was therefore incorrect. The final result was negative.