Prefabricated Solutions for Housing: Modular Architecture and Flexible Living Spaces

Abstract

This research explores the development of a modular prefabricated concrete housing prototype, focusing on sustainability and flexibility. Supported by industry collaboration, it examines three key hypotheses: (1) a rigid geometric modular layout optimizing standardized panels while allowing spatial customization and adaptability, (2) a mixed construction system combining panels with pillars and beams for greater design flexibility, and (3) prefabricated concrete panels with integrated thermal insulation to enhance comfort. An analytical framework was developed based on modularity, flexibility, and sustainability, informed by an extensive literature review and applied to contemporary collective housing case studies. Insights from this analysis guided the development of a housing prototype that integrates modularity, adaptable construction, and sustainable principles. The proposed design follows the principles of design for assembly and disassembly (DFA/DFD), increasingly relevant in modern construction. The findings suggest that combining concrete solutions with thermal insulation, structured around a regular geometric grid, enables diverse housing typologies while ensuring cost efficiency through prefabrication. This approach challenges the monotony of conventional housing, offering visually engaging and functionally adaptable alternatives. It promotes architecture that balances efficiency, sustainability, and aesthetic value while addressing modern housing needs.

1. Introduction

The quest for accessible housing has become a global challenge, intensified by factors such as rapid urbanization, population growth, and economic disparities [1,2,3]. Rising housing demand often leads to surging prices and widening accessibility gaps, making it increasingly difficult for many to find suitable living spaces. As traditional construction methods struggle to keep pace with these demands, innovative solutions are urgently needed [4,5,6].

This article focuses on the intermediate findings of architectural research conducted within the R2U Technologies, Modular Systems project. The goal is to explore prefabricated modular construction housing solutions guided by principles of flexibility and functional adaptability. The project integrates prefabrication processes, and a limited set of modular components designed to respond flexibly to diverse housing typologies, offering a sustainable and scalable approach to contemporary housing.

By leveraging a collaborative effort between academia and industry—supported by the project’s industry partner, Vigobloco—the research benefits from a multidisciplinary team with expertise in architecture, structural systems, seismic behaviors, thermal comfort, energy efficiency, acoustic performance, ventilation, sustainability, and Building Information Modeling (BIM). This diverse collaboration ensures a comprehensive perspective in addressing modern housing challenges.

Central to the project is the development of a prototype for modular prefabricated construction. Designed to maximize versatility, the prototype utilizes a constrained set of prefabricated elements, integrating essential infrastructures such as water, sewer, and electricity. Each module is constructed from prefabricated components and functions as an adaptable apartment, offering interchangeable layouts and customizable features to suit various user preferences and housing typologies, including student residences. The modules can be combined or articulated, providing diverse solutions adaptable to different housing requirements. The modular design also enables rapid assembly and disassembly, supporting sustainable practices like deconstruction and reuse [7,8].

Modularity in construction can be understood in two distinct ways: (1) as a modular construction system based on a rigid geometry framework, using a minimal set of fixed-dimension elements aligned according to strict geometric principles; and (2) as a design approach centered on the aggregation of spatial and/or functional modules. This study adopts the first approach as a starting point. By imposing a fixed orthogonal geometric grid to guide the three-dimensional installation of panels, this research explores the spatial and formal potential of mixed reinforced concrete systems, specifically the combination of pillar/beam structures with prefabricated panels, while adhering to predefined composition rules. As this study represents the initial phase of a broader research development, future works aim to integrate spatial and functional modules within the modular system’s imposed logic, enhancing both adaptability and efficiency [9].

While modular prefabrication has been extensively explored in various parts of the world, its application, particularly in reinforced concrete, remains underdeveloped in Portugal. This gap in implementation presents both a challenge and an opportunity, highlighting the need for further research and innovation to advance modular concrete construction methodologies in the region.

This article emphasizes spatial and dimensional modularity, focusing on design strategies that balance geometry, assembly, and adaptability. These strategies aim to produce flexible, environmentally conscious, and aesthetically pleasing housing solutions. By addressing considerations on the application of modular construction, and typological, structural, and aesthetic considerations, the research underscores the potential of modular prefabrication to meet evolving urban living demands while prioritizing sustainability and efficiency. This research establishes a framework for exploring diverse, high-quality architectural solutions through the application of a repetitive and standardized construction system, which remains adaptable to design customization.

2. Materials and Methods

The initial phase of the research involves a comprehensive literature review focused on key areas relevant to the study: (1) Prefabrication, with a primary emphasis on concrete prefabrication, (2) Modularity, and (3) Flexibility.

In parallel with the literature review, 30 case studies from diverse geographical locations worldwide were selected and analyzed. These case studies were chosen for their alignment with the research themes and their potential to provide meaningful insights for the project. The selected projects were meticulously curated to ensure high-quality and diverse contributions, enriching the overall scope and depth of the research.

The subsequent phase of the study involved research through design.

Research by design is a methodological approach that integrates systematic inquiry into the design process. It emphasizes the iterative nature of design exploration, where research and creative practice unfold simultaneously. Originally developed in architecture and industrial design, this methodology aligns with the cognitive processes of designers, combining intuition, precedent analysis, and reflective practice to generate innovative and context-responsive solutions.

Unlike traditional research methods, research by design does not separate theory from practice but treats them as interconnected. It follows an iterative process of conceptualization, experimentation, and refinement, often addressing complex, “wicked problems” in architecture and urban planning. According to Frayling [10], research by design can be categorized as “research through design”, where the creative process itself serves as a mode of investigation. Similarly, Cross [11] emphasizes the concept of “designerly ways of knowing”, arguing that design functions not only as a problem-solving tool but also as a distinct form of knowledge production—one that differs fundamentally from traditional scientific and humanities-based research methodologies. This approach is particularly valuable for exploring complex, real-world challenges where conventional research methods struggle to capture the richness and dynamic nature of design processes [12]. The findings will be presented using a model informed by the extensive theoretical framework established during the initial phases of the research.

2.1. Literature Review

2.1.1. Prefabrication in Concrete

Traditionally, concrete has been widely used in residential architecture due to its favorable properties. It was mostly used in load-bearing elements; however, recent advancements in concrete technology have expanded its versatility. Today, concrete is produced to serve as an effective insulator and an aesthetic final finish, among other applications [13].

When combined with prefabrication, concrete proves to be an excellent material for achieving efficiency in residential buildings, surpassing the capacities of traditional on-site building methods.

According to authors such as Rocha, Chaucan, and Subramanya, prefabrication has the potential to outdo traditional constructions by many parameters [14,15,16]:

• Manufacturing Efficiency: Prefabrication relies on precise planning in manufacturing, transport, and assembly, making it suitable for diverse architectural designs and standards. Advances in manufacturing technology enable the production of prefabricated elements with some minimal limitations on size, type, or form, due to transportation [17].
• Quality and Comfort: Prefabricated systems offer comfort and versatility in residential units, along with safety features such as high load-bearing capacity and fire resistance. These buildings also provide effective acoustic insulation using floating floors and acoustic breaks [18].
• Construction Efficiency: The combination of on-site assembly of prefabricated reinforced concrete structures with pre-made segments such as utility blocks, lift shafts, stairs, bathrooms, and kitchens, along with dry construction methods for interior finishes significantly reduces labor costs and construction time while ensuring high-quality results [14,19].
• Digitization and BIM: The adoption of Building Information Modeling (BIM) technology in prefabrication enhances visualization, interdisciplinary communication, and overall project efficiency. It streamlines planning, reduces costs, and shortens completion time. BIM also facilitates coordination and integration across design, construction, and management phases [19].

Furthermore, the development of new materials enhances cost-effectiveness, reduces environmental impact, and increases sustainability. The cost of construction, whether prefabricated or traditional, depends on various factors such as location, design complexity, labor costs, and material prices. Although prefabrication offers numerous advantages over traditional construction, it is often still more expensive. Research shows that prefabricated concrete construction is likely to be about 16.3% more expensive than traditional on-site concrete construction [20,21].

However, precast methods can also significantly reduce material expenses by over 50%, lower site labor costs by 30%, provide 4–6% savings from gross floor area exemptions, and eliminate extra charges typically incurred with traditional construction methods. Overall, precast construction aims to reduce costs and increase profitability for all stakeholders [20,22].

Today, especially in Europe, initiatives like the New European Bauhaus aim to create future-oriented, affordable, and accessible housing spaces. Innovative prefabricated construction systems are gaining momentum in the multi-family residential sector across several European countries due to their flexibility, cost-effectiveness, and expedited completion times [19].

2.1.2. Modularity

The term “module” in architecture encompasses a broad and flexible range of meanings, from small-scale measurements to the design and construction of entire buildings. Modularity allows architects to produce versatile solutions that can be adapted to a wide range of conditions swiftly and efficiently [23].

Modular building system combines construction and manufacturing processes that can involve a one-dimensional (1D) single element, two-dimensional (2D) panelized systems, and three-dimensional (3D) volumetric units. These prefabricated components are manufactured off-site and subsequently transported to the construction site, where they are assembled to form complete buildings or substantial parts of buildings [24,25].

Research, including that by Lawson, has demonstrated that modular construction can reduce construction time by up to 50% [26]. This significant time saving is achieved by completing many construction processes in controlled factory environments, then assembling the modules on-site. Approximately 70–95% of the building components, including 2D panelized and 3D volumetric units, were prefabricated in a controlled factory environment [24]. This approach minimizes delays caused by weather and other on-site variables. Additionally, modular construction enhances quality control and reduces labor costs.

One of the most compelling advantages of modular construction is its contribution to sustainability. Modular buildings can be disassembled and reused, aligning with the principles of the circular economy. This approach minimizes waste and maximizes resource efficiency, as components can be repurposed rather than discarded. This is increasingly important in contemporary residential architecture, where there is a growing emphasis on sustainable design practices [13].

Furthermore, modular construction supports innovation in architectural design. Architects can experiment with different configurations and materials, knowing that modules can be easily replaced or reconfigured as needed. This flexibility opens new possibilities for creativity and customization in building design and allows for easy expansion or modification of buildings.

2.1.3. Flexibility

“Home” is a central space in a person’s life. It reflects one’s identity, needs, wants, and desires. Additionally, the lifestyle of people is continuously changing, impacting the meaning and appearance of the standard dwelling. This shift has become even more pronounced recently, particularly due to the COVID-19 pandemic, which forced us to rethink what a home should be. With people spending most of their time at home and unable to leave, homes needed to fulfill multiple functions like work, study, exercise, and rest [25]. Implementing pre-planned flexibility in home design could offer significant benefits in accommodating these evolving needs.

The concept of flexibility or adaptability is not new to architecture. Mies van der Rohe addressed this subject in his theoretical work with the 1951 project, Core House [27]. The idea was to create a house that could be easily produced and built. The space was enclosed by a glass facade, supported only by four external columns, with the interior containing only a service core. Beyond this, the space was left for future inhabitants to configure using furniture and lightweight partitions. The house was designed to be available in three different sizes and adaptable to various climate conditions.

One important question pertaining to flexibility is its definition and its various aspects, being, in architectural terms, the capability or adaptability to change shape, space, or form. According to Tarpio [28] adaptability in architecture can be addressed in various ways and at different scales. It is usually divided into two main categories: ’multifunctionality’ and ’transformability’ [29,30]. Within transformable solutions, several authors further divide this category into subgroups [30,31,32].

• Internal—changes that occur within a spatial unit without changing its overall size.
• External—changes that alter the unit’s size.

As a result, adaptable spatial solutions are suggested to fall into three main categories: multifunctionality, internal transformability, and external transformability. The primary focus of the research and project is on internal transformability.

To design adaptable buildings, it is essential to involve future tenants in the process [33]. Flexibility begins with eliminating inflexibility, which can be economically achieved by reducing load-bearing internal partitions and roof structures, considering technological advancements, and avoiding single-purpose rooms or restricted access designs [34]. Till and Schneider further recommend keeping construction simple, with no load-bearing elements within individual apartments, advocating for skeletal construction [35].

Nowadays, the structure of households has changed significantly. There are more single people and couples without children. Also, many young people, due to the high prices of accommodation, are opting to live with roommates [36]. In addition, for many, living and working are becoming increasingly intertwined [28]. Due to the high prices of housing, creating a project that initially includes only essential features reduces the base cost of the dwelling for both the contractor and the buyers. This approach allows buyers to construct their desired home at their own pace, according to their financial situation. If their needs or preferences change over time, they can easily modify their living space.

This flexibility also enhances sustainability. By readjusting existing spaces, the need for moving from place to place decreases, reducing the demand for new residential dwellings. Outdated spaces can be remodeled and adapted to meet new life challenges, promoting the reuse and efficient use of existing resources.

2.1.4. Synergy of Prefabrication, Modularity, and Flexibility

When prefabrication, modularity, and flexibility are integrated, several advantages emerge:

• Efficiency and Speed: Prefabrication and modularity streamline the construction process, significantly reducing time and labor costs while maintaining high-quality standards [37].
• Sustainability: Modularity and flexibility ensure that buildings can be adapted, reused, or reconfigured over time, reducing waste and the need for new construction. Prefabrication supports this by producing durable and versatile components [38].
• Customization and Adaptability: Flexible design principles allow spaces to evolve with occupants’ needs. Prefabricated modular units can be easily customized and rearranged, providing tailored living solutions that can change over time [39].
• Cost-effectiveness: While prefabrication might initially seem more expensive, the long-term benefits of reduced construction time, labor costs, and the ability to adapt spaces without major renovations contribute to overall cost savings. Flexible, modular homes that can be modified as needed also save costs by extending the functional lifespan of the building [40].

2.2. Case Studies from Practice

Thirty case studies were meticulously chosen based on the main tenets of the project and research objectives. While most of the projects involved prefabrication or included prefabricated elements, this was not the sole determining factor for selection. Other important factors in the selection process included:

• Function;
• Materialization;
• Modulation;
• Flexibility;
• Type of construction system;
• Design quality;
• Location.

The focus was primarily on showcasing case studies of residential architecture, encompassing both single-family and multi-family homes. This decision was driven by the project’s central aim of developing solutions for residential architecture. The research also extended beyond housing to include additional projects that provided valuable insights into structural strategies, façade treatments, material applications, and modular construction techniques. Particular attention was given to projects demonstrating innovative structural methods, such as modular prefabrication, panelized systems, or hybrid construction techniques that integrate traditional and industrialized elements.

The outcome was a comprehensive table summarizing all 30 case studies (see Supplementary Figures S1 and S2 for details), evaluated based on key factors identified as essential for further research:

• Location: indicates the construction site of the project. Therefore, it provides important background information and context for the project:

  -

  Environmental Context: climate, terrain, local ecosystem.

  -

  Cultural and Historical Significance.

  -

  Structural Considerations: seismic activity.

  -

  Social and Economic Factors.

• Method: indicates whether the building was constructed using prefabrication methods or traditional on-site methods.
• Construction System: indicates the type of construction systems used in the projects. This aspect is useful for identifying viable solutions that are structurally safe while also considering aesthetic aspects.
• Material (construction): indicates the material used in the construction system.
• Material (internal walls): shows the material used for non-structural internal walls. This aspect is crucial for understanding and deciding which types of solutions are most appropriate for non-structural internal walls.
• Material (facade structure, facade finish): shows the material used for facades. Similar to the previous point, this allows for understanding which alternatives can be adopted in the project in combination with the concrete of the structural elements and panels.
• Type of modulation investigates the principles of modulation and the components of the modular system used in the case studies. Aligned with ongoing research, it is important to understand the impact of choosing modularization.
• Design principle: identification of the principles that guide the organization of the apartments and their repetition (or absence thereof) in the building.
• Dimension (structural grid): shows the distance between structural elements. Structural requirements vary depending on the different geographical locations of the projects/constructions, impacting the size or distance between structural elements.
• Function: indicates the function of the chosen architectural case studies. Although the initial research included educational buildings, office spaces, and galleries, the final focus was on residential buildings. This criterion was important to fully understand the architecture and its impact on construction and design.

Additional criteria used to obtain a more detailed understanding of the case studies, and the current state of the field itself, include the following:

-

Type of units (number of rooms);

-

Unit area (closed net area);

-

Unit sizes (closed net area);

-

Number of floors;

-

Type of building (communication system).

Subsequently, the selection was narrowed to showcase six case studies (Figure 1) that best aligned with the project objectives in one of the main tenets of the project

• Flexibility: Tila Homes—Pia Ilonen/ILO architects, Helsinki, Finland (2010) [41,42].
• Flexibility and Prefabrication: Wohnregal—FAR, Berlin, Germany (2019) [43,44].
• Prefabrication: Sprzeczna 4—BBGK Architekci, Warsaw, Poland (2017) [45,46].
• Flexibility and Prefabrication: House in Red Concrete—Sanden + Hodnekvam Architects, Lillehammer, Norway (2020) [47].
• Modularity and Prefabrication: 32 Cathedral Homes—Sophie Delhay, Dijon, France (2019) [48,49].
• Modularity and Flexibility: Unité(s) Experimental Housing—Sophie Delhay Dijon, France (2018) [49,50].

Figure 1. Location of selected examples.

Figure 1. Location of selected examples.

2.2.1. Tila Housing

This project executed in Helsinki, Finland, comprises 39 apartments ranging in size from 50 to 102 square meters. The central premise is that the only fixed element in each apartment at the time of purchase is the bathroom, which buyers select from nine available options. This bathroom installation is the only prefabricated part of the project. The apartments have a ceiling height of 5 m, allowing buyers to add a mezzanine later, with the necessary support structure incorporated into the load-bearing walls. To facilitate the moving process, the architect provided new tenants with an instruction manual [41,42] (Figure 2).

Why was this project selected:

Tila Housing showcases the flexibility and adaptability of residential design. By empowering residents to customize their living spaces and incorporating scalable features like mezzanines, the project demonstrates how the project can cater to diverse needs while optimizing space efficiency. This concept could be integrated into our proposal to enhance user engagement and adaptability, aligning seamlessly with our core principle of flexibility.

2.2.2. Wohnregal

Located in Berlin, Germany, this building is a showcase of prefabricated concrete construction. Its structure comprises precast concrete elements commonly used in industrial warehouses, such as pillars, beams, and TT-ceilings, allowing for column-free spaces. The beams span around 13 m, efficiently supporting the building’s framework. Inside, drywall construction delineates the spaces, while the facade features curtain walls. The building serves as a blend of ateliers and apartments, offering spaces ranging from 35 to 110 square meters. The interior spaces are left for future inhabitants to design and modify according to their needs. Remarkably, the entire structure was erected in just six weeks, achieving a cost of EUR 1500 per square meter [43,44] (Figure 3).

Why was this project selected:

Wohnregal highlights the potential of prefabricated construction to deliver cost-efficient, flexible spaces quickly. Its use of industrial construction techniques in a residential setting demonstrates how prefabrication can create versatile environments that adapt to occupant needs. The main aspects of this project including efficiency, adaptability, and cost-effective construction methods align with our proposal’s focus.

2.2.3. Sprzeczna 4

This building located in Warsaw, Poland, was constructed entirely using prefabrication concrete. The design aimed to blend into the historical neighborhood in a contemporary way by using red concrete for the building’s finish, matching the color of the brick facades. The use of prefabricated concrete significantly reduced both the cost and construction time, with the entire process taking approximately 4–5 months. To soften the appearance of the concrete, patterns were imprinted on the surfaces, some of which were created in collaboration with local artists [45,46].

Why was this project selected:

Sprzeczna 4 demonstrates how prefabrication can balance efficiency with aesthetics, achieving cost-effective construction while respecting and enhancing the character of its surroundings. Integrating artistic elements and community collaboration serves as an inspiration for incorporating local identity into prefabricated designs in our proposal.

2.2.4. House in Red Concrete

Aware of rising house prices, architects wanted to contribute to solving this issue with a cost-effective design. This specific project, built in Lillehammer, Norway, was conceived as a prototype that could be repeated in different locations. The house, constructed from red concrete, features a design that utilizes a series of repetitive prefabricated concrete panels. The repetitive facade allowed for the use of the same molds for the concrete elements, helping to reduce costs. Buyers had the freedom to decide on the position of the interior walls. Additionally, the absence of structural walls in the interior allows inhabitants to change the layout according to their needs and desires [48] (Figure 4).

Why was this project selected:

House in Red Concrete exemplifies how repetitive prefabrication techniques can lower construction costs while providing homeowners with remarkable flexibility. Its adaptability and replicability make it an ideal model for affordable housing solutions that align with our proposal’s objectives. Additionally, the design utilizes a limited number of distinct panels, further enhancing efficiency and cost-effectiveness.

2.2.5. 32 Cathedral Homes

The complex, located in Dijon, France, comprises a 32-unit housing complex featuring three distinct dwelling types, adding a fresh perspective on density and architectural diversity. Situated in a suburban landscape, the project blends into the surroundings, recreating the complexity of a residential neighborhood. It includes 22 flats in a six-level building with ground-level parking and a communal terrace. Additionally, five houses connect the main building to a smaller one, which houses five intermediate typologies. The design emphasizes integration over segregation, with all units featuring double-height living rooms and private exteriors. The architecture allows for future densification within existing volumes, utilizing flexible spaces like double-height living rooms that can be adapted over time. The hybrid volume is distinguished by its raw concrete materiality and large aluminum bay windows [48,49] (Figure 5).

Why was this project selected:

The complex 32 Cathedral Homes demonstrates how thoughtful architectural planning can achieve a balance between density and individuality in suburban housing. Its focus on adaptability and integration provides a model for creating dynamic and inclusive communities, an approach that aligns well with the goals of our proposal.

2.2.6. Unité(s) Experimental Housing

UNITÉ(S) is a housing project that redefines living spaces by featuring rooms of identical size, interconnected without hierarchy or predefined function. Located in an industrial area north of Dijon, France, the building’s stepped square design bridges suburban scales and creates a sculpted silhouette. The interior layout is designed to prioritize interiority, allowing inhabitants to freely arrange their living spaces. Each apartment consists of square rooms measuring 13 square meters, offering flexibility in configuration. The construction emphasizes economy of means, with a concrete post-slab structure and lightweight partitions [49,50] (Figure 6).

Why was this project selected:

Unité(s) Experimental Housing showcases how simplicity in design can yield maximum flexibility and efficiency. Its focus on non-hierarchical layouts and economy of construction provides valuable insights into how adaptable housing solutions can meet diverse needs while maintaining affordability, supporting our proposal’s emphasis on user-centric design.

3. Project Case

The third and most critical phase of this study involves drawing conclusions based on our original design, developed within the theoretical framework established in the initial Section of this article. This phase follows the research-by-design approach, integrating systematic inquiry within the design process itself.

3.1. Base of the Proposal

A detailed analysis of the six case studies described in the previous Section was compiled into a table, providing the foundation for defining the premises of the new proposal (the R2U Proposal).

Table 1. New proposed framework (R2U Technology proposition).

	Location	Method	Construction System	Material (construction)	Material (Interior Walls)	Material (Facade Struct.)
Tila Homes	Helsinki, Finland	On site	Column/Beam/ Wall/Slab	Concrete	Panels	Concrete
		Prefabrication				Glass (curtain w)
Wohnregal	Berlin, Germany	Prefabrication	Column/Beam	Concrete	Drywall const.	Glass (curtain w)
Sprzeczna 4	Warsaw, Poland	Prefabrication	Column/Beam/ Wall/Slab	Concrete		Concrete
House in Red Concrete	Lillehammer, Norway	Prefabrication	Wall/Slab	Concrete	Wood	Concrete
32 Cathedral Homes	Dijon, France	Prefabrication	Column/Beam/ Wall/Slab	Concrete	Drywall const.	Concrete
Unité(s) Experimental Housing	Dijon, France	On site	Column/Beam/ Wall/Slab	Concrete	Drywall const.	Concrete
R2U Technologies	Portugal	Prefabrication	Column/Beam/ Wall/Slab	Concrete	Drywall const.	Concrete
	Material (facade finish)		Type of modulation	Design principles	Dimensions (structural grid)	Type of units (no. of rooms)
Tila Homes	Brick		Room	Customizable space	4.6 × 11.7 m	Customizable space
Wohnregal	Glass (curtain wall)		No modules	Fixed layout	2.2 × 11.1 m	0,1,2,3-bedroom apartment
Sprzeczna 4	Concrete panels		No modules	Fixed layout	3.9/4.7/5.4 × 1.7/6.2 m	0,1,2-bedroom apartment
House in Red Concrete	Concrete panels		No modules	Customizable space	3.1/4.1 × 11.5 m	Customizable space
32 Cathedral Homes	Concrete		Unit	Customizable space	3.2/3.4/3.7/4 × 3.7/4.1 m	1,2,3,4-bedroom apartment
Unité(s) Experimental Housing	Metal panels		Part of the unit	Customizable space	3.8 × 3.8 m	1,2,3,4-bedroom apartment
			Room
R2U Technologies			Part of the unit	Customizable space	4.5 × 11 m	Customizable space
			Unit
	Unit area (closed neto area)		Unit sizes (closed neto area)	Function	Number of floors	Type of building (communication system)
Tila Homes	50 m2, 68 m2, 81 m2, 102 m2		4.4 × 11.5 m, 6 × 11.5/9 × 11.5	Multi-unit housing	Gf+5 (6)	Single-loaded corridors
Wohnregal	37 m2–140 m2		5.1 × 8.6/5.1 × 12.8 5.5 × 13.8 m	Multi-unit housing	Gf+5 (6)	Point block access
Sprzeczna 4	28 m2–100 m2		5.1 × 6/7.8 × 6/8.3 × 6 m 8.7 × 6/10.6 × 6 m	Multi-unit housing	Gf+6 (7)	Double-loaded corridors
House in Red Concrete	237 m2		7 × 11.2 m	Single family housing	Gf+2 (3)	Customizable space
32 Cathedral Homes	(a) 55 m2–122 m2, (h) 90 m2–112 m2		(a) 2(7.2 × 9.2)/7.2 × 9.2 (h) 6.9 × 11.4 + 6.9 × 7.3	Multi-unit housing	Gf+1 (2), Gf+3 (4), Gf+5 (6)
Unité(s) Experimental Housing	32 m2, 45 m2, 65 m2, 78 m2		3.6 × 3.6 m (module)	Multi-unitvhousing	Gf+5 (6)	Point block access
						Single-loaded corridors
R2U Technologies				Multi-unit housing		Point block access

represents a synthesis of all the compiled data.

The proposed framework is for a multi-unit building located in Portugal and is based on the following premises: (a) a construction system combining panel/slab and pillar/beam, offering greater flexibility for different organizational layouts and enhanced functional flexibility; (b) creation of adaptable housing modules made from prefabricated elements, incorporating load-bearing walls to separate apartments, ensuring structural integrity and independence for each unit; (c) strategic placement of infrastructure by positioning kitchens and bathrooms in adjacent compartments, aligning water and sewer systems within vertical columns for increased efficiency; (d) interior compartmentalization of apartments using lightweight walls (e.g., drywall) for interior apartment divisions, enabling customization to meet the specific needs of each family or resident; (e) implementation of a structural grid dimension of 4.5 × 11 m; and (f) design of a base panel, in collaboration with Vigobloco, measuring 2.8 m in length, with approximately 2.0 m for the central section and 0.40 m on each side (

Table 2. Base panel sizes.

10 m
7.6 m
5.2 m
2.8 m

).

The proposal centers around the design of adaptable modules constructed from prefabricated concrete elements, where each module functions as a single apartment. These modular units are versatile, offering flexibility in their arrangement to accommodate varying numbers and types of modules used, while maintaining vertical alignment for relevant infrastructures. This modular system supports a wide range of combinations, catering to different functional and programmatic requirements. The combination of different modular articulations of apartments (highlighted purple) and a variety of vertical and horizontal circulation systems (main vertical systems highlighted in blue) facilitates adaptability to different local conditions including topography, solar orientation, urban contexts, morphologies, and social structures (Figure 7).

3.2. Initial Proposal

The further development of one of the proposals enabled testing of the solution at different scales. Initially, the design was conceived for a building consisting of five floors, including the ground floor and four residential levels.

The ground floor, primarily shaped by structural elements, offers flexibility in accommodating various programs, including commercial spaces, services, or an extension of the residential program, such as community spaces, laundry facilities, or bicycle parking. In contrast to the modular residential floors, the ground floor features a distinct exterior design, providing greater freedom in both function and aesthetics. It offers additional functional spaces for the inhabitants, adding value to the living environment. The circulation system includes three vertical circulation cores: a central core with stairs and elevators, and two additional staircases at the end of the horizontal circulation. This layout allows for efficient access and enhances the safety of the structure.

Upper floors are dedicated to residential units, with apartments arranged along exterior galleries to maximize natural light and facilitate cross ventilation. This design reduces the need for artificial lighting and ventilation systems, improving both energy efficiency and air quality. These considerations, combined with the adaptability of the proposed modular system, support the project’s sustainability goals while enhancing the overall living experience for residents (Figure 8).

Incorporating a balcony increases the amount of glass and window space in an apartment, which can lead to higher heat gains, particularly in south-facing buildings. While this passive solar gain is beneficial in the winter by naturally warming the space and reducing energy consumption, it can lead to overheating in summer, increasing reliance on cooling systems [51,52]. To mitigate this, possible solutions could include the implementation of adaptive shading systems that adjust based on the sun’s position, the use of high-performance glazing to reduce heat transfer while maintaining natural light, and the integration of both natural and mechanical ventilation to ensure year-round thermal comfort. These strategies aim to enhance energy efficiency and improve resident comfort.

At a more detailed level, the organization of the residential program within each apartment can be customized to meet the specific needs of individual residents. This flexibility allows for varied interior configurations, such as open-plan living areas or more segmented spaces, depending on the preferences and requirements of the occupants. The infrastructure within the apartments remains uniform across all units, ensuring ease of adaptation and uniformity.

The apartments vary in width, ceiling height (single or double), and the existence of balconies. In terms of width, apartments can span either 2 or 3 modules of the structural grid, with each span measuring 2.4 m. This results in apartments that are either 4.8 m or 7.2 m wide.

The ceiling height options include both single-floor and double-height apartments, with the upper level of the double-height units offering the potential to add a mezzanine, thereby increasing the usable space within the unit. Additionally, the inclusion of balconies in some apartments provides further flexibility, with the size varying to suit different needs and preferences.

These diverse apartment configurations enable the program to cater to a wide range of residents, from single occupants, who prioritize a cozy and efficient layout, to larger families or professionals in need of spacious, multifunctional living areas. This variety ensures the apartments can adapt to different family sizes, personal preferences, and dynamic lifestyle requirements (Table 3).

The inclusion of balconies and terraces in the apartments is a key feature of the proposal, extending living spaces into the outdoor spaces and enhancing the overall experience of exterior areas. These covered spaces can be used year-round for relaxing, dining, or working. The significance of these outdoor areas has been underscored by residents, mitigating the impact of the recent COVID-19 pandemic, which underscored the critical importance of having access to private outdoor spaces for well-being and quality of life. (Figure 9).

Table 3. Apartments layout (colors of the apartments coincide with the colors used in Figure 10).

2 Grid Spans
	Area	Base Form	Position of the Infrastructure	Possible Layouts
Single floor apartment	44 m2
Double floor apartment	40 + 40 m2
3 grid spans
	Area	Base form	Position of the infrastructure	Possible layouts
Single floor apartment	72 m2
	65 m2
Double floor apartment	65 + 65 m2
	57 + 57 m2
	57 + 57 m2

Table 3. Apartments layout (colors of the apartments coincide with the colors used in Figure 10).

2 Grid Spans
	Area	Base Form	Position of the Infrastructure	Possible Layouts
Single floor apartment	44 m2
Double floor apartment	40 + 40 m2
3 grid spans
	Area	Base form	Position of the infrastructure	Possible layouts
Single floor apartment	72 m2
	65 m2
Double floor apartment	65 + 65 m2
	57 + 57 m2
	57 + 57 m2

In addition to the previous considerations, research conducted during the pandemic has shown the significant connection between the indoor and outdoor spaces one inhabits and their impact on mental health [53]. The inclusion of balconies and terraces enhances this relationship, promoting natural light, better ventilation, and a stronger connection to nature, factors that are closely linked to better mental health and increased productivity. Consequently, incorporating such outdoor areas into the design not only addresses immediate comfort and lifestyle needs but also contributes to long-term health benefits, creating environments that foster a sense of calm, balance, and connection to the outside world [54,55].

The exterior appearance of the building is characterized by a combination of materials and the varying depths of the balconies/terraces, which add visual complexity through formal diversity and light/shadow contrast, effectively breaking the monotony of a flat surface. Also, the variation in the depth of the balconies/terraces enhances the facade design by incorporating recessed or protruding areas, thereby introducing a dynamic character to the building’s exterior. Moreover, the differing depths allow for a dynamic relationship with natural light, resulting in shifting patterns of light and shadow throughout the day. The integration of these spatial elements contributes to the visual and functional qualities of the design, providing both aesthetic diversity and a more human-scale experience, which is critical in urban architectural contexts (Figure 10).

The dimensions of the proposal panels (2.8 m, 5.2 m, 7.6 m, and 10.0 m) are based on the data provided by Vigobloco, serving as a base point for the project. As the design evolved, subsequent variations were developed from these base dimensions to accommodate the specific requirements of the project. The idea is to minimize the number of panel types with varying dimensions, thereby streamlining the prefabrication process. By limiting the diverse panel sizes, the proposal enhances efficiency in manufacturing, transportation, and assembly, ultimately optimizing both cost-effectiveness and construction timelines (

Table 4. Panel size variations.

Default length	10 m	7.6 m	5.2 m	2.8 m
Variations length		7.4; 7.2 m	5; 4.6 m	2.6; 2.4; 2.2 m

).

The structural design proposed for this modular building system utilizes load-bearing walls (with or without integrated thermal insulation) and hollow-core slabs. This choice was made because a structural system based on columns and beams, while offering high flexibility, could adversely affect the overall seismic performance of the structure in earthquake-prone regions. Additionally, the connections between the walls are designed to be bolted, with or without coupling plates. This connection type facilitates faster and less complex assembly, while also enabling disassembly or replacement if the connection is damaged under extreme loading conditions [56].

A preliminary assessment of the seismic behavior of this structural concept was conducted, focusing on a five-story modular building (with stair and/or elevator cores conservatively excluded from the analysis). The study employed a nonlinear pushover analysis to evaluate the expected response of the structure in various seismic zones of mainland Portugal [57]. The results indicated promising structural performance, characterized by predominantly elastic linear behavior, even in the most demanding seismic zones, such as Lisbon and Lagos. Given that the stair and elevator cores will contribute additional stiffness and strength, this preliminary study suggests that the proposed structural design is well-suited for regions with moderate to high seismic activity.

Furthermore, in this design, the load-bearing walls and cores are considered the primary structural elements, while any columns and beams added for architectural purposes are treated as secondary seismic elements. According to Eurocode 8—Part 1, this approach facilitates the proper selection of the behavior factor (q-factor), in alignment with the expected structural performance.

At present, experimental validation is ongoing to optimize the solutions for new walls with integrated thermal insulation and improved bolted connections between the load-bearing walls.

4. Results

The study shows several key findings regarding the feasibility and effectiveness of prefabricated modular housing. The proposed system demonstrated a degree of flexibility and adaptability, allowing for diverse spatial configurations while maintaining structural integrity. The modular design supported different apartment sizes and layouts, catering to varied living needs.

The initial design serves as an illustration of one possible configuration within this system. It was developed to showcase the maximum number of apartments that could be accommodated while maintaining efficient vertical circulation through the designated communication cores. Additionally, the design establishes the feasibility of combining single-floor and double-floor apartments without compromising structural stability.

In terms of structural performance, a preliminary nonlinear pushover analysis confirmed that the load-bearing wall system provided sufficient seismic resistance, particularly in high-risk zones such as Lisbon and Lagos. The system maintained predominantly elastic behavior, indicating its reliability in earthquake-prone areas.

Sustainability and energy efficiency were also significant results of the research. The incorporation of balconies, adaptive shading, and passive ventilation strategies reduced the reliance on artificial climate control, improving indoor comfort and minimizing energy consumption.

From a manufacturing and construction perspective, the use of prefabricated panels with standardized dimensions streamlined the building process. This approach minimized material waste, optimized costs, and reduced the need for extensive on-site construction, making the whole process more efficient.

The study also highlighted the urban and social impact of the proposed housing system. The modular approach allowed for customization to suit different occupant needs, from single residents to larger families. The inclusion of communal spaces on the ground floor enhanced social interaction and improved urban livability.

Despite these benefits, the research identified several challenges. High initial investment costs, logistical difficulties in transporting large, prefabricated elements, and regulatory constraints were significant barriers to large-scale implementation. Addressing these challenges will be essential for the successful adoption of modular housing in various urban settings.

5. Conclusions

The research confirms that prefabrication and modularity can significantly enhance housing flexibility, sustainability, and efficiency. The proposed system offers a viable solution for urban housing challenges by integrating adaptable design principles with prefabricated construction techniques. It not only improves living standards through efficient spatial planning and energy-conscious design but also demonstrates strong resilience in seismic regions.

However, widespread adoption requires addressing financial and logistical barriers, refining regulatory frameworks, and increasing market acceptance. Optimizing construction materials, enhancing modular connections for improved seismic resilience, and developing policy frameworks that support modular housing integration into urban planning are necessary for these types of systems to evolve. If these challenges are effectively mitigated, prefabricated modular housing could revolutionize contemporary architecture, providing high-quality, sustainable, and cost-effective living solutions on a global scale.

6. Future Work

Further developments of this project will build on the feedback and new findings provided by experts from various disciplines connected to this project. One key area for advancement is the optimization of prefabricated panel sizes and connection methods to further streamline manufacturing, transportation, and on-site assembly, which can be useful in reducing costs. Research into advanced, eco-friendly materials, such as low-carbon concrete and recyclable composites, can also improve sustainability while maintaining structural integrity. As part of this effort, future phases will incorporate a detailed fire safety analysis, ensuring that material choices and fire protection measures align with regulatory standards.

Additionally, efforts will be made to focus on integrating communal spaces within residential floors to enhance social interaction and community well-being without compromising the quality and privacy of individual units. By carefully designing shared areas such as co-working spaces, lounges, gardens, and recreational zones, residents will gain access to high-quality amenities that foster a sense of belonging and improve overall living conditions. These spaces will be strategically positioned to maximize functionality while maintaining a balance between private and collective living. This approach aims to create more inclusive and engaging housing environments, ensuring that the benefits of modular prefabrication extend beyond individual apartments to the broader community.

Further development may also include expanding the modular system to accommodate different housing typologies, such as single-family homes, student residences, and mixed-use developments, ensuring flexibility across various living needs.