A Natural Language Parameter Catalogue for Algorithm-Aided Design of Modular Housing

Abstract

The construction industry is embracing digital technologies, particularly generative or algorithm-aided design principles. However, integrating these digital tools into design processes while ensuring compliance with rules and regulations remains a significant challenge. This study aims to address this challenge by identifying the essential design parameters and constraints required for semi-automated building model design in the early design stages, with a specific focus on a use case of modular multi-story housing in Vienna. To achieve this, we investigate which parameters are fundamental, how constraints must be formulated, and how these aspects can be covered effectively in the design process. Our research provides a parameter catalog in natural language format to be used for scripting algorithms to generate parametric models. We delineate crucial housing-specific design parameters and identify constraints derived from legal, technical, evaluative, and expert knowledge sources. These constraints ensure that the designs comply with regulations and standards. The findings are organized into eight thematic clusters, each detailing specific conditions, and their interdependencies, thus offering a guideline for scripting algorithm-aided design processes. In conclusion, we propose a conceptual model for translating natural language design parameters into visual programming language.

1. Introduction

The exploration of rules and regulations, implicit expert knowledge, and the formulation of constraints in the context of residential design is resource-intensive and complex. The complexity of exploring such presents a significant barrier to the efficient utilization of digital tools in planning and construction processes. As such, there is a pressing need to streamline and digitize these processes to harness the full potential of digital technologies in the construction industry. By transitioning towards digital solutions, particularly in Building Information Modeling (BIM), there is an opportunity to streamline workflows and enhance efficiency throughout the project lifecycle. To fully realize the potential for improvement in these areas, it is imperative to conduct research focused on BIM-based planning. By harnessing the capabilities of BIM technology, stakeholders in the construction industry can access comprehensive digital representations of buildings, enabling enhanced collaboration, informed decision making, and ultimately, more sustainable, and cost-effective construction practices. In the pursuit of advancing the digital transformation of the construction industry, this paper delves into the fundamental knowledge essential for algorithm-aided Building Information Modeling (AA-BIM) tools, particularly in the context of designing residential buildings. The focus of this research is to elucidate the design-relevant foundational knowledge that such tools must be equipped with during the early stages of design. Residential design and construction involve a myriad of rules, regulations, and implicit expert knowledge that must be translated into a structured and accessible format for algorithmic applications. The inherent complexity of residential buildings introduces a multitude of parameters and constraints, encompassing both explicit requirements dictated by legal frameworks and building codes, as well as implicit expert knowledge aimed at ensuring quality and utility. The results of this study serve as a practical guide for the development of building information models in the early stages of design. This study undertakes a comprehensive exploration, incorporating explicit legal specifications and building code requirements, alongside the implicit expert knowledge necessary for effective residential design. Through a systematic review of the literature, building codes, and implicit expert knowledge, this research identifies and articulates (i) housing-specific parameters, (ii) constraints, and (iii) clustered constraints. These findings are meticulously processed in natural language, providing a tangible and accessible knowledge base.

1.1. Digital Transformation of the AEC Industry, BIM, and Algorithm-Aided Design

The construction industry is increasingly characterized by digitization due to the current state of technology [1,2]. Although digital tools are used in the planning, construction, and operation of buildings, the reuse of digital information in the architecture, engineering, and construction (AEC) sector is very limited compared to other industries like automotive. The automotive industry has achieved significant efficiency gains through digitized, model-based development and manufacturing [3]. In AEC, the complexity of projects and the involvement of multiple stakeholders necessitate constant information exchange, typically via technical drawings. These drawings, created with software mimicking traditional methods, are not fully interpretable by computers. The resulting re-entry is error-prone and inefficient, causing significant data loss and redundant effort at each information exchange point [3]. Further, the potentials of digital technologies in planning, construction process, and management are not yet sufficiently integrated into the planning and construction processes for modular residential buildings [4]. Due to the novel developments in the digitization of the AEC industry in recent years, certain terms are not yet precisely formulated [5]. There are, for instance, various definitions of Building Information Modelling, or BIM for short. For example, BIM is defined as a digital representation of the physical and functional characteristics of a building and, as such, it serves as a shared knowledge resource for information about a facility and provides a reliable basis for decision making during its life cycle from the very beginning [6]. Furthermore, BIM is defined as a cooperative working methodology based on the digital models of a building, with which the information and data relevant to the life cycle are consistently recorded, managed, and exchanged in transparent communication between the participants or transferred for further processing [7]. Sacks et al. [8] define BIM as a set of interacting policies, processes, and technologies that create a methodology for managing essential building design and project data in a digital format throughout the lifecycle of a building. A mathematical definition within BIM states that Building Information Models (BIMs) consist of a given number (n) of 3D elements (3D) to which a sum of information (i) per life cycle phase (t) is assigned and which have a programmed intelligence (I) [9]. BIM is an innovative working method that can be based on digital building models but does not have to be. The focus is on information and not on a 3D model [10]. Current practice’s use of BIM models, however, focuses on explicit information, such as object metadata, complemented by quantity information extraction functions, code reviews, clash detection based on geometric inference, documentation, and parametric design [11,12]. Parametric design is integrated in its basic form into common BIM tools. Parametric objects are defined by the fact that they contain parameters such as distances, angles, and geometric rules and dependencies [8]. The values of the parameters can be changed and lead to different results when modified. When discussing computer-aided design methods, such as parametric design, in the AEC sector, different terminologies are used to address similar approaches. To distinguish computer-aided design terms, Caetano et al. [13] propose an improved taxonomy. Parametric design (PD) can be used as a design process based on algorithmic thought processes. The resulting 3D objects are linked to parameters. Through this connection, it is possible to modify models not on the basis of geometry, but on the basis of parameters, be it height, width, number, etc. In summary, if a design depends on parameters, it can be defined as PD. Generative design (GD) can be understood as a process in which the variants of a design are generated by algorithms. For this purpose, input parameters are required that represent the framework conditions and characteristic values to be analyzed. This results in a vast number of design variants that can be analyzed and filtered according to use. Due to the definition of algorithms, Algorithmic Design (AD) overlaps with the definitions of parametric design and generative design. Nevertheless, in AD there is a correlation between the algorithm and the generated model, which provides traceability and allows the user to identify the parts of the algorithm that generated a particular part of the model. In summary, Algorithmic Design can be described as a generative design approach by a correlation between the algorithm and the model [13]. Algorithm-aided BIM (AABIM), as an extended approach, describes the combination of algorithms with BIM and, due to the definition of Algorithmic Design, also with parametric and generative design. There is currently no official term for the combined form of these two approaches. Aish [14] defines it as “Parametric BIM”, Caetano et al. [15] refer to this method as A-BIM, “algorithmic-aided BIM”, and Humppi and Österlund [16] refer to this approach as “Algorithm-Aided BIM”. Grasshopper [17] and Dynamo [18] are graphical algorithm editors (GAEs) with embedded visual programming languages that allow geometry to be specified by algorithms and provide an interface to the BIM software [16]. Algorithms can be programmed in either textual or visual programming languages [19,20,21]. Visual programming languages allow geometry to be processed with graphical commands without the need for textual programming skills. Consequently, AABIM combines generative processes, based on algorithms, with the creation of BIM objects with metadata. The incorporation of constraints within algorithm-aided Building Information Modelling (AABIM) is imperative for guiding the generative processes and ensuring the creation of compliant, high-quality BIM objects. By integrating constraints based on regulatory requirements, industry standards, and project-specific criteria, AABIM facilitates the optimization of design solutions while automating decision-making processes. These constraints serve as a framework for enhancing collaboration among stakeholders and streamlining the design iteration process, ultimately advancing the digital transformation of the Architecture, Engineering, and Construction (AEC) industry.

1.2. Digital Transformation and Modular Construction

Simultaneously with the digital transformation of the AEC industry, industrial housing construction has also experienced a new dynamic due to the increasing demand for sustainable and affordable housing. In the design and construction processes for modular residential buildings, the potentials of digital technologies are not yet sufficiently integrated into the planning and construction processes. Consequently, providing more affordable and sustainable housing, while creating more housing in a shorter period of time is a major challenge. Large cities will have to create more housing in the future to cope with the rising population. At the same time, the housing created should be able to be rented more affordably and consequently built more effectively [22]. Due to the requirements for ecological and economical buildings, these construction tasks still face great economic challenges today. Studies, such as the investigations into serial housing construction within the framework of the IBA Berlin 2020, attempt to identify possible ways of tackling these tasks [23]. Terms such as standardization, prefabrication, or serial housing construction occur. To counter the problem of housing shortages, especially in urban areas, attempts are being made to find solution strategies for sustainable and cost-effective construction. In addition to urban planning criteria, these should also consider the planning and architectural implementation as well as the economic and social demand structures [24]. Modular construction is seen to solve the problem of housing needs in a sustainable, cost-effective, and time-saving approach. The monetary advantages are also accompanied by shorter and more plannable construction times due to the industrialization of construction [25]. The “new housing shortage” is said to be a social upsurge of serial construction, which was characterized by the architecture of large-scale and prefabricated housing estates in the 1960s to 1980s [23]. This design monotony of architecture was not popular in society and thus led to a stagnation of industrial fabrication [26]. Deficits in housing and quality of life are also associated with serial construction [27]. However, these should not be the result of sustainable and cost-efficient planning and execution. In order to identify possible meaningful savings potential, a precise analysis of the individual cost factors and their impact on the overall project and its quality is required [23]. The recurring problem of the housing shortage today and an alternative solution to combat it was already taken up in the 20th century. Modern architectural culture adopted the idea of rationalization, standardization, and norming from the mass production of the automobile industry. This led to some well-known buildings which were inspired and shaped by developments in construction at the time, such as building materials, transport routes, and assembly functions [27]. The implementation of industrialization in construction, which began in the 1920s, influenced the design of the buildings. Large, prefabricated housing estates are an example of the better, cost-efficient, and faster variant without regard to architecture. Today, the principle of mass customization is used to try to produce serially and individually. The challenge in modular building is to find an intelligent link between standardization and individual requirements and needs to exploit the greatest potential for cost-effective, affordable, sustainable housing that is adapted to the wishes of the users. A module is like a ‘black box’ that hides its complexity on the inside and only flaunts a uniform, standardized user interface on the outside [28]. Today, modular construction tries to break away from the idea of quickly producing the same elements. The development of technology in planning, production, and assembly as well as the different influences in terms of energy, climate technology, and material efficiency model each system into an individual, which in turn can be represented individually [27]. Modular construction is now used in various areas, such as residential buildings, retirement homes, and office buildings. Sustainable building materials are specifically used and, due to the main work in the factory and the extensive planning, the costs for the project are transparent and manageable [29]. The modular construction method is characterized by a longer and more precise planning process as well as monotony in the external design of the building [23]. Moreover, architectural design freedom should not be restricted by standardization [29]. With modular construction, the focus is on design and approval planning, and in cooperation with the modular construction company as the general contractor, new orders can be accepted quickly. Despite this change in working methods, various designers see industrial construction as an opportunity for more efficient and higher-quality work. Methods are developed that advance the streamlining of the building process without neglecting individual and variable design. The implementation of modular housing will increasingly adapt to customer wishes. The production of identical elements that can be used not only in one but in several different projects results in a quality advantage due to the initial, increased time required for detailed planning and work preparation, which in turn leads to a later time saving due to existing data structures [29]. Through the consistency of the processes, quality can be improved above all, which is reflected in the satisfaction of the users [30]. A shift to modular construction requires a new business model that should reduce factors such as construction costs, access to building land, and costs for the user [31,32]. The adoption of modular construction, while offering benefits such as streamlined processes and increased design flexibility, underscores the critical importance of comprehensive knowledge encompassing parameters, constraints, and adherence to rules and regulations. Navigating the complexities of this construction method requires a nuanced understanding, from parameter-based design approaches to the meticulous development of constraints. Embracing these elements is pivotal not only for overcoming resistance to change in planning and project management but also for ensuring the successful implementation of modular construction. The integration of well-defined constraints and adherence to regulations serve as the foundation for achieving efficient, high-quality outcomes, ultimately contributing to user satisfaction and realizing the full potential of this innovative construction approach.

1.3. Parameter-Based Design

The vast majority of multi-story residential buildings are highly similar in various respects, yet almost every residential building is unique, adapted to the individual environmental conditions. Designers need to adapt designs to different building sites and project conditions, and at the same time plan as efficiently as possible. Tried and tested “building blocks” (such as room proportions, exterior walls, staircases, building depths, openings, sizes, etc.) are used which must, however, be modified and reassembled iteratively in order to meet the individual project requirements. A generalized and universally applicable model of housing that can always be used is simply impossible. This results in an extensive and time-consuming planning effort that often becomes a gauntlet between law, design, society, urban planning, and property-specific regulations. One way to reduce the high effort of conventional planning is to use parameter-based modeling. The fundamental idea is to create the design target, in this case, a model of a residential building, by entering and adjusting the descriptive parameters. However, parameter-based design on a residential building model is dependent on a broad knowledge base. How such a knowledge base can be built up is roughly outlined in this section. For the above-mentioned “building blocks” of housing, all the parameters required for modeling must be derived. If the parameters found are linked to the rules of housing construction, fixed values or requirements that must always be met result, and validity ranges in which they may be changed, or their use is selectable. The parameters regulated in this modality are referred to as constraints. However, the high complexity of a residential building inevitably leads to a vast number of constraints that are difficult to manage. To maximize the use of the constraints for parameter-based modeling, a far more applicable construct is needed. Such a construct can be done by grouping all the constraints that influence and/or depend on each other. Such a group is specified as a cluster. Individual design elements can thus be defined by a specific cluster assigned within the required parameters.

1.4. Research Background and Research Question

The complexity and resource-intensive nature of exploring rules, regulations, implicit expert knowledge, and formulating parameters and constraints in residential design present significant challenges. Our previous study, part of a research project on a digital platform for affordable housing [33], presented as a conference paper [34], focused on the exploratory determination and cataloging of preliminary housing-specific parameters and preliminary specifications for design guidelines. Our objective is to develop an algorithm (script) within a visual programming editor (Grasshopper3D-Rhino3D v.7), which will be linked to the BIM software (such as Archicad 27). This tool is conceptualized to enhance modular off-site production in multi-story housing, promoting affordable and sustainable housing design. Figure 1 illustrates the scope of the current study in relation to the previous study, divided into two main sections: the previous study and the scope of this study.

Previous Study:

• The preliminary parameters and conceptualization of the AA-BIM tool

Scope of This Study:

• The top section in Figure 1 outlines the inputs for creating the parameter catalog, including the analysis of modular residential buildings, implicit expert knowledge, analysis of sources, and the definition of parameters.
• These inputs contribute to the parameter catalog, which is organized into three super-categories: room, unit, and building, each with various constraints.

The underlying framework (Figure 1) as our point of departure [34] relies heavily on implicit expert knowledge as input for the algorithm-aided generation of digital models, which as a limitation overlooks crucial aspects and fails to comprehensively capture relevant parameters considering the demands of law, standards, regulations, building technology, housing quality, and requirements. This limitation highlights the need for a more systematic and comprehensive approach to parameter analysis and constraint formulation in the design process. To address these challenges, this research aims to develop a comprehensive parameter-based knowledge base. Therefore, there is a need to transition towards a more robust and systematic approach that encompasses thorough design parameter analysis to ensure compliance with use case relevant parameters. In summary, the problem statement emphasizes the necessity for a shift towards comprehensive parameter-based analysis and constraint formulation in residential design to overcome the limitations associated with implicit expert knowledge and ensure the development of efficient and compliant digital models.

The research question on the creation of a knowledge base is divided into three sub-questions (on parameters, constraints, and clusters):

• RQ: How can a parameter catalog be created that considers the demands of the law, standards, regulations, building technology, and housing quality?

To address the main research question, we focus on two specific sub-questions:

• SQ1: Which parameters are of fundamental importance for the design of multi-story housing, and how should these parameters be defined?
• SQ2: How should constraints and thematic clusters be formulated to address the regulations, conditions, and limits associated with the identified parameters?

2. Methodology

This section delineates the research design aimed at constructing a comprehensive parameter catalog, comprising parameters and constraints. Illustrated in Figure 2, the methodology is elaborated upon in subsequent sections, progressing from the identification of housing-specific parameters to the sourcing and definition of constraints, culminating in the elaboration of clusters. The methodology employed for this study incorporates a quality gate as a pivotal element in the iterative process, guided by Qualitative Data Analysis (QDA) principles. The data undergoes an initial phase of immersion, allowing for a period of reflection. Subsequently, an inductive coding approach is applied to the data, facilitating the extraction of emergent themes and patterns. Furthermore, the data are subjected to a deductive coding process, aligning with the housing parameters outlined in our previous study [34]. This deductive approach provides a structured framework for analyzing the data, ensuring that they are systematically categorized based on predetermined criteria. The combination of inductive and deductive coding methodologies enhances the comprehensiveness of the analysis, capturing both unforeseen insights and aligning with established housing parameters for a more comprehensive understanding. Each stage of the research design, illustrated in Figure 2, is meticulously described in the following sections: Section 2.1 Definition of Housing-Specific Parameters, Section 2.2 Identification of Sources and Definition of Constraints to Section 2.3 Elaboration of Clusters, offering insights into the systematic approach employed. Ultimately, this research design provides a roadmap for the development of the knowledge base.

2.1. Definition of Housing-Specific Parameters

Under the definition of parameters, the requirements, characteristics, functions, and dimensions necessary to describe a design aspect are summarized. To determine the parameters, the umbrella term housing, which encompasses the entire structure, is broken down into 3 subcategories: (i) the individual room, (ii) the independent dwelling unit, and (iii) the entire building (residential complex). For these subcategories, a parameter catalog describing them at a label, parameter, qualitative variable, and preliminary requirement levels was developed. The housing-specific parameters derived [34] have their limitations, of course. Since the analyzed set of data has a very specific scope, further research in the particular identification of legal sources, technical sources, evaluation systems, and implicit expert knowledge is required to define constraints, which is elaborated in the following sections.

2.2. Identification of Sources and Definition of Constraints

Sources had to be identified that consider the defined housing-specific parameters in an Austrian context. Legally binding standards and regulations, such as the Vienna Building Code [35] and Austrian Institute for Building Technology Guidelines [36], are mandatory. The Austrian Standards [37] used were identified via a keyword search in the Austrian Standards Directory. Keywords derived from the parameter catalog, such as fire protection, accessibility, ventilation, space requirements, etc. were applied. In order to meet the demands for quality and usefulness, further technical literature (

Table 1. Parameters of a room: supercategory, category, and subcategory.

Supercategory	Category	Subcategory
Room	Light	Natural
		Artificial
	Ventilation	Natural
		Mechanical
	Thermal Comfort	Heating
		Cooling
	Openings	Doors
		Windows
		Ventilation Openings
	Connections	Power Supply
		Water Supply
		Sewerage
		Media/Telecable
	Floor Area	Aspect Ratio
		Spatial Proportion
		Furnishing
	Load Capacity of Slabs, Walls and Flooring
	Surfaces	Flooring
		Ceiling
		Walls
	Sanitary Facilities	Number of Sanitary Rooms
		Equipment

), additional data, and various housing evaluation systems (Table 1) were researched. These sources were investigated, especially to cover areas with limitations that were not yet or not sufficiently covered by the previous sources. The aim was to cover the information needs of all the defined parameters through the sources on different aspects of housing. To clarify the step-by-step procedure for defining individual conditions from various sources and to generate a sum of individual conditions that are as similar as possible from the various contents, it is necessary to follow a constant procedure of identifying relevant information, reducing it to essential contents, paraphrasing it into main statements, and normalizing these statements for consistency and coherence, as detailed in the following:

• Identification: This step entails identifying relevant text passages, paragraphs, statements, values, diagrams, and tables that pertain to a planning aspect or its parameters. It involves a comprehensive review of sources to extract pertinent information related to housing construction.
• Reduction: After identification, the next step is to reduce the identified information to its essential contents. This involves distilling values, limit values, concrete restrictions, and regulations that are specifically applicable to housing construction. Irrelevant or extraneous details are omitted to focus solely on essential information.
• Paraphrasing: In this step, the reduced information is paraphrased to articulate main statements that regulate the specific properties of planning aspects or parameters. Each statement corresponds to the definition of a constraint, clearly specifying the requirements or restrictions related to a particular aspect of housing construction.
• Normalization: Finally, the paraphrased core statements are normalized to ensure consistency, independence, functional dependence, and freedom from redundancy. This process ensures that the information is organized in a structured and coherent manner, facilitating easy interpretation and utilization [38].

2.3. Elaboration of Clusters

A cluster always focuses on only one parameter. It regulates this parameter comprehensively and independently, contains the necessary, elaborated boundary conditions, and occurs only once. The elaboration of the clusters depends on the definition of constraints. In the first phase, the individual sources are still considered independently of each other. If several constraints were defined within a source that refer to the same parameter, they were connected by a common subcategory. This subcategory is titled by the respective parameter. The complete table of elaborated constraints corresponds to this structure. In the next phase, the sources are considered jointly. If a cluster contains several constraints from different sources that regulate exactly the same property, only the strictest or legally binding remains. This procedure is comparable to normalization as used in the design of databases. The requirements for the individual information in a normalized table are independence, functional dependence, and freedom from redundancy. If a parameter is not yet sufficiently regulated in this respect by the data found in the sources, it is supplemented by constraints based on implicit expert knowledge. In order to manage the vast number of clusters, grouping into further supercategories has been conducted. They refer to the superordinate aspects of design, such as building site utilization, accessibility, or technical building equipment. This described procedure for creating the clusters is shown in Figure 2.

3. Results

This section unveils the outcomes of the research, encompassing (i) the methodology (ii) delineated parameters crucial for housing-specific design, (iii) the identified constraints addressing the conditions and limits associated with these parameters, and (iv) the resultant clusters derived from the formulated constraints. These cover various aspects of design at an early design stage, providing a structured framework for guiding algorithm-aided design processes. The detailed presentation of these results elucidates the foundational components of the knowledge base.

3.1. Housing-Specific Parameters

In our previous study [34], parameters were meticulously structured based on the levels of label, parameter, and qualitative variable. This categorization led to the identification of supercategories comprising the parameters of a room, parameters of a dwelling unit, and parameters of a building. While this framework provided a structured approach to understanding building design elements, a significant challenge persists in the lack of standardized terminology and definitions for subsystems within buildings. From individual rooms to larger functional zones, inconsistent terminology hampers the effective description and integration of building subsystems, particularly concerning interfaces with other systems. This lack of uniformity complicates the development of automated building models, hindering seamless interactions and interoperability. Thus, there is a critical need to establish a standardized terminology for describing building subsystems to address this challenge effectively. The supercategories defined in this study include the (i) parameters of a room, (ii) parameters of a dwelling unit, and (iii) parameters of a building. These initial supercategories serve as a point of departure and underscore the further need for a unified terminology. The resulting parameters and their detailed descriptions are presented in the following sections of this paper.

• Parameters of a room

A room is formed by one or more segments, either structurally through enclosing surfaces like facades, walls, or ceilings or organizationally. The excerpt from the parameter catalog, titled “Rooms”, delineates the diverse parameters characterizing various rooms within a housing unit. Each room possesses unique usage profiles, necessitating the application of different parameters to suit its specific function. While certain parameters are mandatory across all the rooms, others are utilized to a limited extent or are applicable only to particular rooms. Table 1 offers a parameter catalog excerpt, providing visual clarity on the distinct parameters associated with different rooms within the dwelling unit.

• Parameters of a dwelling unit

A zone comprises one or multiple rooms (with horizontal, vertical, or mixed extent), such as a corridor, a floor, or an atrium. A dwelling unit zone consists of the grouping of several rooms, different in their type and functionality, which in their interaction enable the use for residential purposes. The size of dwellings varies greatly according to the number of mandatory and secondary rooms as well as the size of the individual rooms. A distinction is made between mandatory and secondary rooms. Mandatory rooms are required, according to implicit expert knowledge, to enable the use of the unit for residential purposes in its interaction. Supplementary, or secondary rooms are defined as additional rooms that extend the functions of the unit. A graphical representation of the parameter catalog excerpt “Dwelling Unit” is presented in

Table 2. Parameters of a dwelling unit: supercategory, category, and subcategory 1 and 2.

Super Category	Category	Subcategory 1	Subcategory 2
Unit	Mandatory Rooms	Room	Room 1
			Kitchen
			Room 1 + Kitchen
		Sanitary Rooms	Bathroom
			Toilet
			Bathroom + Toilet
		Connection between mandatory rooms
		Entrance Area	Hall
	Total Usable Area
	Supplementary Rooms	Room	Room 2
			Room 3
			Room n
		Functional Room	Storage Room
			Pantry
		Sanitary Rooms	Bathroom 2
			Toilet 2
			Utility Room
		Outdoor Area	Balcony
			Loggia
			Garden
			Sunroom

.

• Parameters of a building

A building comprises one or multiple zones. In addition to the dwelling units, the overall concept of the building includes the general requirements, technical building equipment, planning factors, engineering factors as well as the additional or general requirements associated. An excerpt from the building-specific parameter catalog is shown in

Table 3. Parameters of a building: supercategory, category, and subcategory 1 and 2.

Super Category	Category	Subcategory 1	Subcategory 2
Building	Technical Building Equipment	Media
		Sanitary Piping
		Ventilation
		Power Supply
		Thermal Comfort
		Shaft	Number
			Position
			Size
		Lift System	Operating Room
			Shaft Size
	General Requirements	Accessibility
		Circulation	Staircase
			Access to Units
			Lift
		General Areas	Laundry Room
			Universal Usage Room
			Private Storage
			Bicycle Room
			Youth Space
			Stroller Area
	Engineering Factors	Type of Structure	Solid
			Frame
			Mix
			Superstructure
		Components	Load bearing
			Non-load bearing
	Planning Factors	Fire Safety	Material
			Compartment
			Escape Route
		Housing Mix
		Building Physics	Vapor Diffusion
			Sound Proofing
			Insulation
			Damp Proofing
		Building Site	Development
			Height
			Built Up Area

.

3.2. Sources and Constraints

From the identified housing-specific parameters, the origins of the constraints were established, as depicted in

Table 4. Sources of legal, technical, evaluation, and implicit expert knowledge.

Type	Content Description	ID
Legal Sources
	Viennese Building Code	BOW
	Austrian Institute for Building Technology—Guideline 2—Fire Protection	OIB 2
	Austrian Institute of Construction Engineering—Guideline 3—Hygiene, health and environmental protection	OIB 3
	Austrian Institute of Construction Engineering—Guideline 4—Safety of use and accessibility	OIB 4
	Austrian Institute of Construction Engineering—Guideline 6—Energy saving and thermal insulation	OIB 6
	Austria Standard B1600, Building without barriers—Design principles	Ö-Norm B1600
	Austria Standard B8110 -Thermal insulation in building construction	Ö-Norm B8111
	Austria Standard H5411—Sanitary appliances	Ö-Norm H5412
	Viennese Housing Promotion and Housing Rehabilitation Act of 1989—provisions for the subsidisation both of the construction of new housing units and the rehabilitation of existing residential buildings and dwellings	WWFSG
Additional Data
	Survey on Microcensus Labour Force 2019 (average of all dwellings in one year)	MZA
	Survey on Microcensus Housing 2019	MZW
	Survey on Viennese dwellings by dwelling size and municipal districts 2011	WWG
Technical Sources
	Document on floor plan design in housing	K
	Investigation into the economic viability of flexible housing systems	RFLEX
	Housing value comparisons and evaluation of different dwelling types	RWBW
	Document on Viennese residential typologies	P
Evaluation Systems
	Total Quality Building: Total Quality documents the quality of a building from planning through construction to use in the TQ Building Certificate	TQB
	Cost Benefit Tool: Enables a systematic comparison of the costs and the benefits of buildings	KNT
	Housing Evaluation System: The Housing Assessment System WBS is a tool for planning, assessing, and comparing residential buildings	WBS
	Housing Value Barometer: Rating system for sustainable housing quality that can be used to comprehensively assess and evaluate flats, residential buildings and housing complexes.	WWB
Implicit Expert Knowledge		EX

Refs. [35,36,37,39,40,41,42,43,44,45,46].

. The objective was to gather comprehensive information on each parameter, considering construction technology, quality standards, and usage requirements. To achieve this goal, a diverse array of sources was necessary. Table 4 outlines the legal, technical, evaluative, and implicit expert knowledge sources that were qualitatively examined to delineate the constraints.

Table 4 is categorized into different types of sources, each playing a crucial role in defining constraints for automated construction processes. Legal sources, including the Viennese building code and guidelines from the Austrian Institute of Construction Engineering, establish the regulatory framework. Additional data, such as surveys on housing, offer valuable insights into societal and demographic aspects. Technical sources, such as documents on floor plan design and investigations into flexible housing systems, contribute to technical perspectives. Evaluation systems, such as Total Quality Building and the Housing Evaluation System, provide tools for assessing building quality. The table also includes implicit expert knowledge, highlighting the importance of tacit knowledge in constraint formulation. Overall, this diverse range of sources ensures a comprehensive approach to defining constraints for housing-specific design on a Viennese use case.

Figure 3 presents housing-specific parameters and the corresponding documents, standards, and guidelines that were utilized to formulate constraints for each parameter. It outlines various aspects such as construction class, method, built area, site boundaries, building height, outline, and more. Each parameter is associated with one or multiple sources, including regulations like the Viennese building code (BWO), implicit expert knowledge (EX), documents on floor plan design in housing (K), cost–benefit tools (KNT), surveys on microcensus labor force and housing (MZA and MZW), building standards (B1600, B8110, and H5412), Austrian Institute of Construction Engineering guidelines (OIB 2, OIB 3, OIB 4, and OIB 6), documents on Viennese residential typologies (P), economic viability and housing value comparisons (RFLEX and RWVW), and evaluation systems (TQB, WWB, and WBS). For example, the construction class parameter is only covered by the “BWO”, Viennese building code source. Flexibility is covered by expert knowledge, the TQB evaluation system, and the investigation into the economic viability of flexible housing systems. This helps in understanding how different aspects of housing design are regulated or influenced by multiple sources of standards and expert knowledge. The matrix reveals that BWO and EX are the most comprehensive sources, covering a wide range of parameters and thus serving as robust references. Among the parameters, Living Spaces, Sanitary Rooms, and Ventilation stand out as the most referenced, underscoring their importance across various sources. On the other hand, sources like MZA, MZW, B8110, H5412, and P appear to be highly specialized or limited in scope, as they reference only a single parameter each. This differentiation highlights the breadth of information available in some sources while indicating a focused or niche relevance in others.

3.3. Clusters of Constraints

A cluster encompasses a collection of conditions essential for governing its fundamental characteristics. Each condition within a cluster is self-contained, pertaining to the parameter from which it derives its title, and strives to eliminate redundancy. Moreover, the clusters provide an evaluation of the constraints concerning their adaptability.

Organized into clusters such as building plot utilization, building technology, residential complexes, residential (dwelling) units, rooms, accessibility, windows and doors, and technical building equipment, eight clusters have been delineated. Subsequent clusters often build upon the settings established in preceding ones. For instance, the building’s depth may dictate whether a bathroom is situated on the facade or within the interior. This, in turn, affects decisions regarding ventilation systems—mechanical or natural—and subsequently impacts requirements for openings or technical building equipment. Figure 4 represents the defined clusters, and the subsequent sections (1 to 8) provide the detailed descriptions of each cluster.

3.3.1. Building Site Utilization

The first cluster regulates the geometrical properties of the model to be generated, based on the plot-specific conditions.

Table 5. Excerpt of the building site utilization cluster.

Building Site Utilization
Construction class (cc)
	construction classes 1, 2, 3, 4, 5, and 6 are specified in the development plan
Construction design
	a > open construction: Free-standing buildings. Compliance with the minimum distances from the building site boundaries.
	b > coupled construction: Buildings built on 2 adjacent plots, detached on all the other sides. Free-standing buildings are still possible if the townscape is not disturbed. If the neighbor has already built onto the property line, the building must also be built onto the property line.
Built-up area
	the built-up area is defined as the vertical projection of the above-ground stories, including all the space-creating or space-supplementing components (structurally enclosed on all the sides or only open on one side).
	in construction methods a, b, c, and d, the built-up area may not exceed 30% of the building site area.
Building plot boundaries
	distance of the building from the neighboring property line in the case of open construction and in the case of the open fronts of coupled construction:
	cc 1 and 2: ≥6 m		cc 4: ≥14 m		cc 6: ≥20 m
	cc 3: ≥12 m		cc 5: ≥16 m
Definition of building height
	buildings with a depth of ≤15 m	building height: The perpendicular distance between the verifier surface and the uppermost point of intersection of the outer wall with the street front and roof surface. Gable walls must be considered, but a maximum of 50 m2 per wall and 100 m2 per building may be disregarded.
Building height
construction class min. height max. height	cc 1	cc 2	cc 3	cc 4	cc 5	cc 6
	2.5 m	2.5 m	9 m	12 m	16 m	21 m
	9 m	12 m	16 m	21 m	26 m	-
Building outline
	the resulting building outline to be adhered to may be exceeded to the extent absolutely necessary by individual, non-spatial parts of subordinate size as well as staircases and lift shafts.

illustrates an excerpt of the building site utilization cluster. The cluster provides a comprehensive overview of the regulations pertaining to building site utilization within different construction classes. It outlines various aspects including construction design, built-up area limitations, requirements for building plot boundaries, the definition and limits of building height, and specifications for building outline. For instance, it categorizes construction classes from one to six as specified in the development plan and delineates construction designs as open (a) or coupled (b), with corresponding guidelines for minimum distances from property boundaries. The table also details restrictions on built-up areas relative to the building site area and defines minimum and maximum building heights for different construction classes. Additionally, it addresses exceptions to the building outline regulations, allowing slight deviations for specific architectural elements such as staircases and lift shafts when necessary.

3.3.2. Structural Engineering

This cluster is dedicated to the basic structural properties that need to be defined to enable the automatic generation of a model. The aim is to select the structural system and define the dimensions and superstructures of all the components. It contains superstructures that can be used in residential construction [47].

Table 6. Excerpt of the structural engineering cluster.

Structural Engineering
Structural load-bearing system in multi-story residential buildings
load bearing walls	longitudinal wall systems—outer and middle walls bearing along the longitudinal direction of the house
	transverse wall systems—walls load-bearing across the longitudinal extension of the house every 5–6 m
Flexibility
	a load-bearing system with few fixed points inside the flat increases flexibility
	a total of 15% of the usable floor space of the building with room height should be ≥2.8 m to enable conversion to a sales room/office. The ground floor is the best
Thermal insulation
	minimum requirements for the u-value of the individual components:
	u-value of ground-floor slabs ≤0.40 w/m2 k	≤0.40 w/m2 k
Sound insulation
	all the building components must contain the transmission of airborne sound, impact sound, and structure-borne sound (also from building services equipment)
	staircases and lifts should not be directly adjacent to bedrooms
General requirements for building components
	protection against penetration and the rise of moisture from the ground (also foreseeable/hundred-year floods)
	protection against precipitation water through all the exterior building components
Selection of components from a linked component catalogue
	based on the selection of the load-bearing system, only those components should be displayed from the component catalog that satisfy the settings

illustrates an excerpt of the structural engineering cluster. It includes specifications for load-bearing systems, emphasizing longitudinal and transverse wall systems and their distribution within the structure. Flexibility criteria are defined, advocating for load-bearing systems with minimal fixed points to enhance adaptability, particularly for commercial conversions. Thermal insulation standards are established, with minimum requirements for the u-value of ground-floor slabs. Sound insulation guidelines cover airborne, impact, and structure-borne sound transmission, recommending the spatial separation of staircases and lifts from bedrooms. General requirements ensure protection against moisture and precipitation water, including flood prevention measures.

3.3.3. Building Unit

The cluster regulates the settings for the orientation of the building, which consider solar radiation and noise sources. Further, accessibility and fire protection, as well as aspects regarding general areas are regulated in this cluster.

Table 7. Excerpt of the building unit cluster.

Building Unit
Building depth and orientation
	do not orientate common rooms (except the master bedroom) to the north
	for east–west-oriented flats, the building depth can be greater than for north–south-oriented flats.
Access
staircase-system	access to all the flats directly through the stairwell
	single, double, triple, quadruple, and multi-story systems theoretically possible
Hallways
	clear passage width main aisles ≥1.2 m.
	clear passage height ≥2.1 m.
Ramps
	longitudinal slope ≤6%.
	clear passage width ≥1.2 m.
Stairs
	clear width of main stairs ≥1.2 m.
	clear passage height ≥2.1 m.
Lifts
	for new buildings with more than 2 main floors, a passenger lift is mandatory.
	all the floors must be interconnected
Fire protection
	corridors and stairs in the course of escape routes: clear width ≥1.20 m. for more than 120 persons: +10 cm per 10 persons.
	maximum length from the flat entrance door to staircase/external staircase/into safe open space ≤40 m.
General rooms
	provide a bicycle storage room and a bicycle room—1 bicycle parking space per 30 m2 of usable floor space.
	if possible, provide a general garden/open space/roof terrace.

illustrates an excerpt. It includes directives regarding building depth and orientation, emphasizing the avoidance of north-facing common rooms. Access requirements detail staircase-system options and specifications for hallways, ramps, stairs, and lifts, ensuring accessibility standards are met. Fire protection measures mandate clear widths for corridors and stairs along escape routes and set maximum distances to safety areas. Additionally, provisions for general rooms advocate for bicycle storage facilities and outdoor spaces to enhance residents’ quality of life.

3.3.4. Dwelling Unit

Table 8. Excerpt of the dwelling unit cluster.

Dwelling Unit
Usable (net) floor area (NFA)
	usable floor area of a unit ≥30 m2 NFA ≤150 m2
	unit size	1 room	2 room	3 room	4 room
	usable floor area	≥30 m2	≥45 m2	≥60 m2	≥80 m2
	unit size	5 room	6 room	7 room
	usable floor area	≥100 m2	≥120 m2	≥140 m2
Spatial program
	no. of rooms	1R	2R	3R	4R	5R	6R	7R
	no. of bedroom		1	1	2	3	4	5
	separate bedroom		1	1	1	1	1	1
	living without a dining area							1
	living with dining area	1	1	1	1	1	1
	extra dining room							1
	kitchen/cooking area	1	1	1	1	1	1	1
	bathroom with wc	1	1			1	1	1
	bathroom without wc			1	1
	extra wc			1	1	1	1	1
General requirements
	flexibility	flats should be flexible -> few fixed points. Necessary fixed points collected or in the peripheral area of the flat.
		Fixed points in the residential unit are the flat entrance, the lighting side, sanitary, and kitchen connections.
Housing mix
	housing mix (example)	type	%
		1 room	10%
		2 room	35%
		3 room	40%
		4 room	10%
		5+ room	5%
		share of the largest housing group is <30–40%.
					At least 3 different housing groups with a share of ≥10% each

outlines the parameters within the dwelling unit, which addresses the entirety of individual residential units. It includes regulations for usable floor space, spatial programs, general requirements, and options for housing mix settings. The usable floor area defines the size and spatial layout based on the number of rooms, ensuring flexibility and adhering to specific size limits. The spatial program details the allocation of rooms, such as bedrooms, living areas, dining areas, kitchens, and bathrooms, providing a comprehensive guide for designing residential units. The general requirements emphasize flexibility in design, encouraging a layout with few fixed points and specifying essential fixed points within the residential unit. Lastly, the housing mix provides an example distribution of different apartment sizes (e.g., 1 room, 2 room, etc.) as a percentage of the total units, promoting diversity in housing options with specific size percentages to achieve a balanced mix. The overall aim is to enable flexibility, functionality, and a diverse housing mix.

3.3.5. Room

Table 9. Excerpt of the room cluster.

Rooms
Clear room height
	for recreation rooms, a clear room height of ≥2.5 m applies.
	the clear room height of rooms other than occupied rooms must be ≥2.1 m.
Common rooms
	all recreation rooms must be naturally lit and ventilated.
	door and window surfaces must not project into the bed area.
Cooking area
	kitchen should always be naturally lit and ventilated
	variants	kitchen—alone, self-contained
		kitchen with dining area for all persons—self-contained
Dining area
	unit size	1 room	2 room	3 room	4 room	5 + room
	seats	2	3	4	6	8
	size dining	≥2.5 m2	≥4.5 m2	≥5 m2	≥6.5 m2	≥8 m2
	dimensions	≥1.6 × 1.6 m	≥1.6 × 2.7 m	≥1.8 × 2.7 m	≥2.4 × 2.7 m	≥3.0 × 2.7 m
Sanitary rooms
	variants	bathroom and wc in one room
		separate bathroom and separate wc
		bathroom and wc in one room + second, independent wc
Anteroom/corridor/access
	there must be an anteroom
	width of anteroom/corridor ≥1.2 m
Private outdoor area (balcony/loggia/terrace)
	unit size	1 + 2 room	3 + 4 room	5 + 6 room	7 + room
	size outdoor area	≥3 m2	≥4 m2	≥5 m2	≥6 m2
	depth outdoor area ≥1.4 m
Closet space
	not obligatory. If available, it makes sense to connect to the bedroom.
	adapt dimensions to wardrobe module 60 × 60 cm + 90 cm deep movement area in front of it.
Storage area
	not obligatory. If available, it makes sense to assign it to the entrance area or kitchen.
Additional requirements due to furnishability
	doors and windows must have a furniture-free area of 120 cm on both sides.
	In front of windows only furniture ≤80 cm high and ≤60 cm deep

presents a summary of the diverse requirements for the various types of rooms within the residential space planning context, encapsulated in this cluster. It emphasizes the use-specific aspects essential for designing functional and comfortable living spaces. Each set of rules within the cluster addresses general requirements applicable across multiple rooms or those specifically tailored to individual rooms. The parameters within this cluster address various aspects such as room height, common rooms, cooking areas, dining areas, sanitary rooms, anterooms/corridors/access areas, private outdoor areas, closet space, storage areas, and additional requirements for furnishability. Each set specifies dimensions, configurations, and other criteria to ensure the optimal utilization and functionality of each room type. These regulations aim to enhance the overall quality of living and the usability of residential spaces.

3.3.6. Accessibility

The requirements for the accessible design of dwellings refer to both the dwelling unit and the generally accessible areas of the residential complex and are dealt with in this dedicated focus.

Table 10. Excerpt of the accessibility cluster.

Accessibility
General
	in the case of residential buildings with more than 2 flats, the requirements for accessibility (equipment, sanitary rooms, corridor width, doors incl. approach areas, furnishings, …) must be able to be met easily or without great effort through structural changes, if necessary.
	load-bearing components should not have to be changed.
Sanitary rooms
	in case of adaptable barrier-free planning: partition wall between bathroom and wc in lightweight construction without pipe routing.
	minimum size of barrier-free wc 2.15 × 1.65 m
Cooking area
	a turning circle with a diameter of 1.5 m should be inscribable.
Entrance area
	a turning circle with a diameter of 1.5 m must be inscribable.
	anterooms must have a clear width ≥ 1.2 m. Partial narrowing ≤ 10 cm to a length ≤1 m is permissible.
Doors
	in front of flat doors, a turning circle with a diameter of 1.5 m must be inscribable.
	approach area in the opening area of the door 2.0 × 1.5 m. on the other side of the door 1.5 × 1.2 m.
Residential complex
	at least the main entrance or an entrance in its immediate vicinity must be accessible without steps.
	connecting paths must be free of steps, thresholds, or similar obstacles. Level compensation by ramps or passenger lifts/vertical lifting devices.

presents a comprehensive overview of accessibility considerations within residential buildings. It outlines guidelines and criteria aimed at ensuring easy access and maneuverability for individuals with mobility challenges. The constraints cover various aspects, including general accessibility requirements for residential buildings with multiple flats, specifications for sanitary rooms to facilitate adaptable barrier-free planning, criteria for cooking areas to accommodate inscribable turning circles, standards for entrance areas ensuring adequate space for maneuverability, and regulations for doors, including approach areas and inscribable turning circles. Additionally, the table addresses accessibility standards for the residential complex, emphasizing the importance of accessible entrances without steps, obstacle-free connecting paths, and provisions for level compensation using ramps or lifting devices where necessary. This cluster aims to create inclusive environments that accommodate the needs of all the residents, promoting accessibility and ensuring equal access to residential amenities and facilities.

3.3.7. Windows and Doors (Openings)

Table 11. Excerpt of the windows and doors cluster.

Windows and Doors
Window size
	finished parapet height ≥ 85 cm
	finished parapet height ½ window reveal depth ≥ 100 cm (height ≤ 12 m)
View
	unobstructed view from window ≥ 2 m measured horizontally from façade line
Protection against overheating (summer)
	window area proportion on the external façade < 30% or solar control glazing
	movable external shading system towards east and west
Doors
	usable width of headroom ≥ 80 cm
	usable height of headroom ≥ 2 m

provides an overview of the windows and doors within residential buildings. These establish guidelines and standards aimed at ensuring the functionality, safety, and efficiency of windows and doors. It specifies criteria such as window size, view requirements, protection against overheating in summer, and dimensions for doors. Regarding window size, the finished parapet height should be at least 85 cm, and the product of half the parapet height and the window reveal depth must be at least 100 cm for fall heights up to 12 m. For views, the windows must offer an unobstructed horizontal view of at least 2 m from the facade line. To prevent overheating in summer, the window area on the external facade should be less than 30% or utilize solar control glazing, and movable external shading systems are required for the windows facing east and west. In terms of doors, the usable width and height of the door headroom must be at least 80 cm and 2 m, respectively.

3.3.8. Technical Building Equipment

The content of

Table 12. Excerpt of the building equipment cluster.

Technical Building Equipment
Heating
	recreation rooms and bathrooms must be heated in such a way that a room temperature sufficient for the intended use can be achieved.
	in the case of radiator heating, at least 1 radiator in each recreation room and sanitary room.
Ventilation
	common rooms and sanitary rooms must be adequately ventilated by windows, doors, etc. leading directly into the open air.
	in sanitary rooms and kitchens, windows leading directly into the open can be dispensed with if mechanical ventilation is available.
Lighting
	all rooms must be additionally and independently illuminated
Shafts
	manhole size for a single downpipe ≥ 15 × 15 cm (rain pipe, kitchen waste pipe,...)
	manhole size for water supply and disposal ≥ 25 × 25 cm

offers a condensed overview of technical building equipment. The focus is deliberately narrowed to aspects directly impacting spatial design and building structure, acknowledging the vast scope of technical building equipment in the construction industry. These are guidelines for incorporating essential elements into the automatic model generation during the early design stage. These address essential aspects such as heating, ventilation, lighting, and shafts, all of which have a direct impact on spatial design and building structure. Additionally, guidelines for the size of shafts for drainage and ventilation purposes are defined to ensure proper functionality and efficiency within the building. For heating, it specifies that recreation rooms and bathrooms must be heated adequately, with at least one radiator required in each room for radiator heating. Ventilation rules require common and sanitary rooms to have proper ventilation, either through windows or doors leading outdoors, with mechanical ventilation acceptable in some cases. Lighting rules mandate that all the rooms must have additional and independent illumination. Finally, shaft rules dictate minimum manhole sizes for downpipes and water supply/disposal to ensure proper functionality.

4. Proposed Model

This study places emphasis on refining the methodology itself and articulating parameters and constraints in natural language, laying the groundwork for future digital model implementations. This proposed model, Figure 5 and

Table 13. Proposed model—translation of natural language into code in visual programming.

Step	Description	Output
Parameter	List all the relevant parameters described in natural language.	List of parameters
Source	Extract and define specific constraints from natural language sources.	Extracted constraints
Constraints	Break down and interpret constraints, resolving ambiguities and redundancies.	Human-readable descriptions (qualitative and quantitative)
XML (optional)	Translate NL into an XML format for structured representation.	Human + machine-readable XML documents
VPL Algorithm	Convert NL into visual programming nodes and connections using Grasshopper.	Visual programming language algorithm (nodes + logic)
BIM Model	VPL algorithm to generate the final Building Information Model.	BIM Model

, encompasses a vast array of considerations, spanning from geometric intricacies to legal factors, all tailored specifically for the realm of housing design. A critical aspect is the translation of natural language constraints into machine-readable formats, a challenge that underscores the need for continuous refinement and validation. While natural language provides nuanced understanding, formal languages are essential for machine processing. To facilitate the translation of natural language design rules into code within a visual programming environment like Grasshopper, we propose a structured approach that transforms natural language parameters into machine-readable instructions. By implementing these strategies, we aim to bridge the gap between natural language design guidelines and executable code within Grasshopper, enabling designers to leverage the comprehensive knowledge base for automated model generation and analysis. Finally, the visual programming language algorithm is to be used to generate the Building Information Model (BIM).

Figure 6 illustrates an example of the translation of natural language constraints into a visual programming language (VPL) script inside the software Grasshopper (Grasshopper3D-Rhino3D v.7) defining construction classes and corresponding building heights based on the input curve of the footprint of a building. The parameter catalog categorizes buildings into six construction classes (CC 1 to CC 6), each with specified minimum and maximum heights. For instance, construction class 1 (CC 1) ranges from a minimum height of 2.5 m to a maximum of 9 m, while construction class 4 (CC 4) spans from 12 m to 21 m. The VPL script starts with the user selecting a construction class, which determines the range of permissible building heights. The script then calculates a list of potential building heights within the specified range. Using an index, the script selects a specific height from this list, which can wrap around if the index exceeds the list length. This selected height is scaled using a factor and combined with a unit vector to produce the building volume geometry. This example demonstrates how natural language constraints can be translated into a VPL script by converting the textual descriptions of construction classes and building height regulations into a structured, visual programming format.

5. Discussion

Based on a comprehensive approach integrating parameter definition, systematic literature review, building code and regulations review, and implicit expert knowledge, a novel knowledge base has been developed. The main focus of this study lies in the methodology itself and the definition of parameters and constraints articulated in the natural language format. These serve as a foundational design guideline intended for future implementation into digital model generation. These models are based on a comprehensive array of parameters spanning geometric, non-geometric, technical, legal, economic, and environmental considerations. For instance, they include building site utilization parameters such as construction class (e.g., construction classes 1, 2, 3, 4, 5, and 6), design (e.g., open construction requiring minimum distances from plot boundaries, coupled construction with specific distance requirements), built-up area limits (e.g., may not exceed 30% of the building site area), and building plot boundaries (e.g., distance of building from neighboring property line ranging from ≥6 m to ≥20 m depending on the construction class). Additionally, they cover structural engineering aspects like load-bearing systems (e.g., longitudinal and transverse wall systems), flexibility for future conversions (e.g., 15% of usable floor space with room height ≥ 2.8 m), thermal insulation (e.g., U-value of ground-floor slabs ≤ 0.40 W/m² K), and sound insulation (e.g., transmission control for airborne, impact, and structure-borne sound). General requirements also include protection against moisture and precipitation. Room-specific parameters such as clear room heights (e.g., recreation rooms ≥ 2.5 m, other rooms ≥ 2.1 m), natural lighting and ventilation, dining area sizes (e.g., 1 room ≥ 2.5 m², 5 + rooms ≥ 8 m²), sanitary room configurations, and private outdoor spaces (e.g., outdoor area size ranging from ≥3 m² to ≥6 m²) are considered to ensure compliance with legal standards and to meet user needs effectively. Requirements include easily achievable or structurally feasible modifications for accessibility (e.g., partition walls in sanitary rooms without pipe routing, the minimum size of barrier-free WC 2.15 × 1.65 m, turning circles with a diameter of 1.5 m in cooking and entrance areas, and clear anteroom width ≥ 1.2 m). Door approach areas must be ample (e.g., 2.0 × 1.5 m on one side, 1.5 × 1.2 m on the other), and main entrances or their immediate vicinities must be step-free, with connecting paths free of obstacles. In compliance with the legal standards, these models incorporate regulations from various authoritative sources, including the Viennese building code (BOW), Austrian Institute for Building Technology guidelines on fire protection (OIB 2), hygiene, health and environmental protection (OIB 3), the safety of use and accessibility (OIB 4), energy saving and thermal insulation (OIB 6), and multiple Austria Standards [37] such as B1600 for barrier-free design, B8110 for thermal insulation, and H5411 for sanitary appliances. Additionally, provisions from the Viennese Housing Promotion and Housing Rehabilitation Act of 1989 (WWFSG) are considered. The culmination of this effort results in the housing-specific parameters, constraints, and clusters within the knowledge base. The methodology presented in this study serves as a foundational framework for the systematic development of a knowledge base for model generation processes, primarily focused on residential buildings in Vienna. By delineating a structured approach from the identification of housing-specific parameters to the elaboration of clustering, the methodology provides a roadmap for constructing a usable knowledge base. This systematic design is crucial for scalability, allowing for future expansions, modifications, and adaptations. However, it is important to acknowledge certain limitations. The methodology’s development is anchored in a specific use case in Vienna, potentially limiting its generalizability to other regions with distinct regulatory, cultural, and environmental contexts. The knowledge base may lack inclusivity and may not fully capture the diverse requirements of different stakeholders in various geographical locations. Therefore, ongoing research should focus on incorporating multiple use cases from diverse contexts, ensuring the methodology’s adaptability and comprehensiveness across a broader spectrum of residential construction scenarios. Continuous refinement and validation are essential to enhance the methodology’s robustness and address limitations associated with its singular origin. The overarching aim is to establish constraints that uniformly, clearly, and comprehensively regulate various aspects of modern residential construction. The presented clusters themselves are of course not without limitations or need for further research. Standards and regulations are constantly evolving. One of the primary challenges in defining clusters is that standards and regulations are not static; they are subject to frequent updates and revisions. A notable example is the Viennese building code, which has undergone numerous amendments over the years. Since its establishment in 1930, it has been updated more than 70 times, with significant revisions occurring in 1935, 1947, 1960, 1985, 1991, 1996, 2001, 2012, 2018, and most recently in 2023. This constant evolution necessitates the continuous monitoring and integration of new standards into existing clusters to ensure compliance. New perspectives and standards are emerging that will also continuously influence the demands on planning, design, and quality of housing. The continuous development of the knowledge base is therefore indispensable. Further, the most decisive step in creating valid constraints that can be used is the choice of sources. Various sources, whether the legal or technical literature, provide general statements on topics relevant to planning, but only a few works provide concrete and measurable statements. Furthermore, the application of this method revealed possible limitations in three respects. Firstly, the creation is a theoretically endless process in which more and more far-reaching and detailed constraints can be incorporated. On the other hand, a detailed examination of the legally valid standards and regulations reveals a strong tendency towards regulating the structural aspects of residential construction. Design factors concerning floor plans, functionality, and quality of the living space remain largely unregulated. While this allows for a high degree of individuality in design, the high demands on functionality, quality of living, and the comfort factor remain unaddressed. The definition of uniform standards for these aspects is lacking. Thus, in this study, mainly the design-specific literature [40,41,44,48] and implicit expert knowledge were used to formulate these constraints in order to define planning factors, floor plans, functionality, and quality of living space. The third challenge is the future translation of the natural language into code, for example visual programming language. Visual programming language inside Graphical Algorithm Editors, such as Grasshopper, is flow-based and consists of a series of nodes representing a part of a code as well as a basic unit of programming. This graphical representation provides the possibility to represent design rules in a machine- and human-readable language, whereas natural language is only readable by humans and not automatically processable by machines. Natural language rules are ambiguous and contain contextual clues and abstract information, have considerable levels of redundancy to compensate for uncertainty and reduce misunderstanding, while formal languages are less redundant and more concise and are developed to provide machine-readable, unambiguous data representations. Extensible markup language (XML), readable by both humans and machines, potentially represents the next step in future research (Figure 5). However, transferring data requires considerable effort. Due to the complexity of the rules, experts have to interpret and identify the hidden logic of the rules; thus, the natural language layer may not be bypassed. Future research should focus on integrating a broader range of sources, including more concrete and measurable guidelines, to create more robust and comprehensive clusters. This may involve collaboration with regulatory bodies and industry experts to identify and incorporate emerging standards. Developing dynamic clustering methods that can adapt to evolving standards and regulations will be crucial. This could involve the use of machine learning algorithms to automatically update clusters as new data and standards become available. Moreover, future research should aim to create a more balanced approach to clustering by incorporating both structural and design-related constraints. This could involve developing new metrics and criteria that specifically address the quality of living spaces, functionality, and comfort. Emphasizing user-centric design considerations in future research will help ensure that clusters address not only regulatory compliance but also the needs and preferences of end-users.

6. Conclusions

In conclusion, this study has tackled a critical aspect of digital tools for automated building model design by addressing the design-relevant knowledge they must access. Further, the parameters of fundamental importance for the design of multi-story housing are defined. Finally, constraints and thematic clusters are formulated to address the regulations, conditions, and limits associated with the identified parameters. With a focus on methodology, the research aims at scalability beyond specific use cases for broader applicability in automated construction processes. This knowledge base integrates the diverse requirements of law, standards, regulations, construction technology, housing quality, and implicit expert knowledge. The key outcomes of this research are the definition of constraints and the formulation in natural language format, which serve as crucial components for guiding generative design processes. The research methodology commenced with the identification of parameters essential for housing-specific design at the early design phase, with a focus on geometric and planning relevant aspects directly applicable to residential buildings. Subsequently, the study explored the formulation of constraints to address the regulatory, contextual, and limitative aspects associated with these parameters. The aim was to develop constraints that offer concrete and measurable statements, aligning with legally applicable frameworks, state-of-the-art standards, and user-specific requirements for housing quality. This study has addressed the complex task of defining parameters and developing constraints essential for housing-specific design. Through a systematic approach, the parameters were categorized into three levels: parameters of a room, parameters of a dwelling unit, and parameters of a building unit, each tailored to specific functional requirements within the housing context. The delineation of the parameters for rooms within a housing unit considered the diverse usage profiles, ensuring that each room type was accurately characterized. This was visually represented in the parameter catalog providing clarity on the unique characteristics associated with different rooms. Moving to the parameters of a dwelling unit, the study emphasized the cohesive grouping of rooms to form residential units, considering both mandatory and secondary rooms. This category provided insights into the variability in dwelling unit sizes and the distinction between essential and supplementary rooms. The parameters of a building unit further expanded the scope to encompass broader aspects of residential construction, including technical building equipment and engineering considerations. The comprehensive approach of the building unit-specific parameter catalog highlighted the multifaceted nature of housing design. Constraints were derived from a diverse array of sources, ensuring saturation of information on individual parameters while aligning with construction technology, quality standards, and requirements. The development involved integrating constraints into structured clusters, resulting in eight defined clusters oriented towards conventional phased residential planning. These clusters provided a systematic framework for addressing the key aspects of early-stage design, from building site utilization to technical building equipment. In summary, this study emphasizes the importance of a holistic approach to parameter definition, constraint formulation, and cluster development in advancing automated design processes. The resulting knowledge base serves as a valuable resource for guiding future research and development efforts in the field of automated design, facilitating more efficient and effective processes. While this study presents advancements, it is imperative to acknowledge its limitations and the need for ongoing research. One of the challenges posed by natural language processing is accurately interpreting and integrating diverse and complex regulatory requirements into automated systems. Natural language often contains ambiguities and variations that make it difficult to translate into precise, actionable constraints. Despite these challenges, the structured parameter-based constraints offer a robust framework that can be further refined and expanded as natural language processing techniques improve. The dynamic nature of standards and regulations necessitates the continuous development of the knowledge base to remain up to date with evolving demands on planning, design, and quality. Additionally, the use of natural language poses challenges, as they are not automatically processable by machines. Nevertheless, the parameter-based constraints in natural language established in this study provide a foundation for guiding future research and development efforts in the field of automated generative design processes. This foundational work is essential for advancing the integration of automated design processes with evolving standards and regulations, ensuring both compliance and innovation in future research efforts.