Design of a Shipping Container-Based Home: Structural, Thermal, and Acoustic Conditioning

Abstract

The construction of buildings using shipping containers (SCs) is a way to extend their useful life. They are constructed by modifying the structure, thermal, and acoustic conditioning by improving the envelope and creating openings for lighting and ventilation purposes. This study explores the architectural adaptation of SCs to sustainable residential housing, focusing on structural, thermal, and acoustic performance. The project centers on a case study in Madrid, Spain, transforming four containers into a semi-detached, multilevel dwelling. The design emphasizes modular coordination, spatial flexibility, and structural reinforcement. The retrofit process includes the integration of thermal insulation systems in the ventilated façades and sandwich roof panels to counteract steel’s high thermal conductivity, enhancing energy efficiency. The acoustic performance of the container-based dwelling was assessed through in situ measurements of façade airborne sound insulation and floor impact noisedemonstrating compliance with building code requirements by means of laminated glazing, sealed joints, and floating floors. This represents a novel contribution, given the scarcity of experimental acoustic data for residential buildings made from shipping containers. Results confirm that despite the structure’s low surface mass, appropriate design strategies can achieve the required sound insulation levels, supporting the viability of this lightweight modular construction system. Structural calculations verify the building’s load-bearing capacity post-modification. Overall, the findings support container architecture as a viable and eco-efficient alternative to conventional construction, while highlighting critical design considerations such as thermal performance, sound attenuation, and load redistribution. The results offer valuable data for designers working with container-based systems and contribute to a strategic methodology for the sustainable refurbishment of modular housing.

1. Introduction

Shipping containers (SCs) were first introduced in 1956 by Malcolm McLean to standardise cargo handling across ships, trucks, and warehouses. Constructed of durable cor-ten steel, these containers are designed to withstand harsh conditions. Although they may show signs of ageing over time, their structural integrity often remains intact, making them suitable for reuse in architectural projects.

The International Organisation for Standardisation (ISO) and the International Convention for Safe Containers (CSC) have established specifications for SCs, which focus on structural strength, serviceability, durability, and various applications. Containers are produced in a variety of sizes, typically 8 feet (2.44 m) to 53 feet (16.15 m) in length. Among these, the 20-foot (6.09 m) and 40-foot (12.19 m) models are the most widely used. A particularly popular variant is the High Cube (HC) container, which features an external height of 9.5 feet (2.9 m, 20’HC or 40’HC) for increased storage capacity.

This study explores the architectural adaptation of SCs to sustainable residential housing, focusing on structural, thermal, and acoustic performance.

One of the distinctive contributions of this work is the in situ assessment of the acoustic performance, an aspect rarely addressed in literature on shipping container architecture [1,2]. While previous research has advanced the thermal and structural evaluation of refurbished containers, experimental data on façade airborne sound insulation and floor impact noise remain scarce. Through specific design strategies, SCs can achieve the sound insulation levels required by residential building codes.

1.1. Container-Based Buildings

In 2024, global containerised trade experienced a strong rebound, with total volumes reaching 183 million twenty-foot equivalent units (TEUs), marking a 6.2% increase compared to 2023. This growth was primarily driven by the growing demand for containerised goods, particularly in Asian markets. According to the UNCTAD Review of Maritime Transport for 2024, containerised trade is projected to grow by 3.5% in 2024, assuming continued stabilisation of global supply chains. This recovery contributes to a projected 2.4% broader growth in overall maritime trade. Looking ahead to the 2025–2029 period, UNCTAD anticipates average annual growth rates of 2.4% for total seaborne trade and 2.7% for containerised trade [3].

The use of shipping containers in architecture, commonly referred to as container architecture, has gained increasing attention because of its affordability, modularity, and potential for sustainable development. Research in this field has explored a wide range of applications, including low-cost housing, emergency shelters, and student accommodation. Studies have examined adaptability, thermal performance, urban integration, and life cycle assessments of design, particularly highlighting the environmental and economic benefits of container-based housing solutions, with a focus on student housing [4].

Furthermore, the versatility of containers in various architectural typologies, from residential units to public infrastructure, has been investigated. Technical challenges and issues related to user acceptance in container-based housing have also been addressed. Discussions have focused on modular design strategies and typological adaptations aimed at optimising container-based constructions [5], as well as contextual analyses that explore their implications for urban environments and integration into existing architectural fabrics [6].

In addition, empirical metrics have been presented that compare the sustainability of container architecture with conventional construction models [7]. Furthermore, how container-based developments contribute to the transformation of contemporary urban landscapes has been examined [8], and climate responsiveness and material constraints in retrofitted containers have been evaluated.

Despite the advantages associated with reusability and waste reduction, container architecture faces several limitations, particularly in areas such as thermal and acoustic insulation, structural adaptability, and compliance with acoustic building codes.

1.2. Advantages and Limitations of the Use of Shipping Containers in Construction

Incorporation of shipping containers [SCs] into architectural design and construction offers a series of well-documented advantages. The following are among the most notable [9]:

• Reduced construction time: SC-based buildings demonstrate a significant reduction in project duration, with estimates suggesting a 30% decrease compared to conventional construction methods;
• Cost-efficiency: the average cost savings for SC-based construction is also estimated to be approximately 30% relative to traditional building techniques;
• Modularity: the intrinsic modularity of SCs eases a straightforward expansion by adding additional units, allowing flexible spatial configurations;
• Environmental sustainability: SC-based construction aligns with sustainability goals by reducing CO₂ emissions and incorporating principles of material reuse and recycling;
• Global availability: shipping containers are widely available due to their standardised production and global distribution;
• Transportability: their standardised dimensions and structural robustness allow efficient truck transport, facilitating deployment to remote or temporary sites;
• Architectural flexibility: despite uniform dimensions, containerised construction supports diverse design strategies and compositional variations through modular assembly.

However, the architectural application of SCs also presents significant challenges. Currently, there is no universally accepted design standard for container-based construction, and the mechanical and thermal properties of modified SCs remain poorly defined. The limited internal width of standard containers (2.44 m or 8 feet) is insufficient for conventional living spaces such as lounges or double bedrooms. As a result, lateral faces are often removed to expand the interior dimensions, potentially compromising structural integrity. Computational simulations have been used to assess the mechanical behaviour of containers subjected to various structural modifications [8].

A major limitation lies in the lack of standardised data regarding the mechanical properties of the steel used in container fabrication, which often consists of profiles not marketed as structural elements. This complicates structural analysis and load bearing predictions [10].

Shipping containers have emerged as an economical and sustainable construction alternative housing entity, stimulating the creativity of architect and designers [11]; however, they face inherent thermal challenges, including low thermal inertia and poor insulation, which result in increased energy consumption. To address these issues, recent research has proposed design strategies aimed at optimizing the energy performance of container-based buildings in different climate regions.

Shen et al. [12] evaluated the reuse of shipping containers in three European climate zones—cold, temperate, and hot–humid—under historical and 2050–2080 climate projections. They proposed a generic modular home integrating passive design strategies, a low surface-to-volume ratio to reduce envelope exposure, advanced insulation using vacuum insulation panels, phase change materials (PCMs) for thermal storage, and photovoltaic systems on roofs and façades, with the aim of achieving a net-positive energy balance. Bianco et al. [13] investigated, by means of dynamic thermal simulations, the climatic adaptability and energy efficiency in diverse European contexts, assessing 30 European locations representing a range of Köppen–Geiger climate zones from Mediterranean to subarctic areas, confirming that container houses are highly sensitive to climatic context.

Design strategies have been proposed for tropical [14] and subtropical climate conditions [15] for the years 2050 and 2080. Using building performance simulations, the influence of different insulation type and thickness, window-to-wall ratios (WWRs), and air infiltration rates has been examined, providing a framework for climate-adaptive design. Additionally, Elrayies G. M. [16] verified that synthetic materials like polyurethane insulation are effective and compatible with a hot-humid climate, and Thanekar et al. [17] suggest that window geometry is an essential initial consideration because the orientation, structure, window properties, and location of a shipping container affect users’ thermal comfort.

Beyond their application in subtropical regions, container structures have been studied as temporary housing in tropical climates, particularly for post-disaster scenarios. Their modularity, resilience, and availability make them suitable for rapid deployment [18]. Nonetheless, thermal simulations in hot and humid contexts reveal that current designs experience significant fluctuations in indoor temperature and humidity, negatively impacting occupant comfort. Notably, building orientation does not appear to significantly improve these conditions, in contrast with the finding in Southwest Europe, where the western orientation generates less energy demand compared to the less favourable orientation, which is the southern one [19]. Effective thermal retrofitting in humid climates therefore requires not only insulation layers for thermal, acoustic, and fire protection but also vapor barriers, climate-appropriate interior finishes, and fittings to meet ASHRAE comfort standards, considering both environmental and occupant-related variables.

Future climate adaptation potential has also been assessed in studies following standards guidelines. For instance, Alegbe M. [14] evaluates the thermal comfort and energy efficiency under climate conditions expected in Africa for 2080.

Moreover, as post-pandemic architecture, prefabricated shipping containers to create spaces that have higher standards of safety with regard to diseases and that also serve several functions for human activities, not only on the scale of an individual building but also on a larger scale, like student housing, have been studied [20] in an attempt to explore these uses, considering cases in Europe and project proposals in Egypt.

Studies conducted by Tong et al. [21] have investigated the influence of insulation thickness on heating energy consumption and associated carbon emissions, as well as payback periods across varying service lives, for shipping containers used as temporary housing during the Beijing 2022 Olympic and Paralympic Winter Games, taking into account two different altitudes.

From an environmental perspective, life cycle assessment (LCA) comparisons between container-based housing and conventional lightwood-frame houses indicate no significant differences in overall environmental impact when built to base code or upgraded to passive and energy-efficiency standards [22]. However, reusing containers via the cut-off method substantially reduces CO₂ emissions and energy use compared to recycling at end of life. Repurposing containers for permanent housing thus presents an opportunity to address affordable housing needs while maintaining environmental parity with conventional construction. Furthermore, while energy-efficiency upgrades can lower operational impacts, they may simultaneously increase embodied impacts during the construction phase [14,22].

Studies by Giriunas et al. [10] investigate the structural behaviour of ISO shipping containers repurposed for non-shipping applications, such as housing and modular buildings, particularly structural capacity after modifications. The authors conclude that while unmodified containers can meet ISO structural standards, modifications must be carefully evaluated through simulation and testing to ensure safety. Hoffman et al. [23] address the scarcity of standardized guidelines for the repair, refurbishment, and maintenance of shipping containers used in structural applications, particularly in non-shipping contexts, developing a framework for assessing and restoring the structural integrity and compliance in building applications. Moreover, addressing repair recommendations focuses on replacing or reinforcing critical structural members, using welding and bolted connections that preserve load paths, as well as emphasizing the importance of material compatibility, corrosion protection, and adherence to welding standards.

Blanford and Bender [11] highlight the importance of maintaining structural integrity when modifying shipping containers, and in addition, Zafra et al. [18] suggest placing openings for windows and doors away from the corner posts to reduce the stress and tension on the overall container structure.

To improve thermal performance and energy efficiency, SC envelopes are commonly upgraded by adding insulation layers. For example, the thermal resistance (R-value) of an SC wall can increase from approximately 1.0 m²K/W to 3.7 m²K/W with the application of vacuum insulation panels [24]. Furthermore, natural insulation materials have been investigated to improve thermal performance and indoor comfort [25].

Detailed thermal analyses, including infrared thermography and envelope performance measurements, have been performed to assess thermal bridges, air infiltration rates, and solar heat gains through fenestration. These studies provide valuable information on envelope deficiencies and inform strategies to improve thermal comfort in SC-based dwellings [26].

Although used containers offer lower initial costs than new units, their prior maritime service poses potential health hazards due to residual pesticide treatments. These must be completely removed to ensure safe human habitation. Despite this, the reuse of SCs extends their useful life cycle and reduces environmental impacts. Life cycle assessment (LCA) studies indicate that a modular SC-based house with improved thermal performance can produce a 28% reduction in total life cycle costs compared to a similar light-wood-framed building [22]. LCA comparisons with conventional construction also highlight advantages in emissions reduction, energy savings, and recycling potential [27].

In addition to thermal and environmental optimisation, this study also addresses the acoustic performance of containers, an aspect still scarcely documented in the literature. Most previous works have focused on laboratory tests or isolated case studies, with few reporting in situ measurements under real-use conditions [1,2]. By providing field evidence, this work helps bridge the current knowledge gap and supports the advancement of container-based construction as a sustainable and acoustically reliable building solution.

1.3. Case of Study

Technical innovation is at the heart of the transformation of shipping container construction from a simple recycling solution to a sophisticated building system. This section details technical and constructional changes, thermal and acoustic design methodologies, and structural modifications that enable the effective use of shipping containers as modern construction.

The case considered is a single-family home built based on four containers (Figure 1) in Parla, a city located in the Madrid community (Spain). The architects were Javier Pinilla Melo, coauthor of this article, and Francisco Esteban Aguado, and the construction company was “Reformas y Mantenimientos Neo”.

The house is semi-detached, with a basement for a garage; a ground floor with a living room, a kitchen, and a bathroom; and a first floor with three bedrooms and two bathrooms (Figure 2, Figure 3 and Figure 4).

1.3.1. Modular Coordination and Typological Design

One of the most notable innovations in container-based construction is the use of modular coordination. This design approach treats each shipping container as a standardised modular unit that can be combined in a multitude of ways to achieve diverse spatial configurations [3].

This approach has the following advantages.

• Efficient spatial arrangements: by treating containers as modules, it can design layouts that optimise space, accommodate varied room typologies (such as living or working, sleeping, circulating areas), and adjust to client-specific requirements;
• Adaptability and flexibility: the modular strategy allows for easy addition, subtraction, or superpositions of units, thereby enabling dynamic alterations in spaces as the needs of the occupants evolve;
• Standardisation: the standardised dimensions of ISO-compliant containers provide predictable and repeatable building elements, which greatly simplifies the integration of these modules into a coherent overall design.

1.3.2. Refurbishment Process and Quality Control

A critical technical innovation in shipping container construction is the centralisation of the refurbishment process. The refurbishment process involves several sequential steps to prepare containers to be used as building modules.

• Creation of openings: precision cutting to create windows, doors, and other features necessary for habitation;
• Insulation installation: thermal and acoustic insulation is applied to meet building code requirements, reduce thermal bridge, and enhance occupant comfort;
• Surface preparation and finishing: painting and coating the container to protect against corrosion and improve aesthetic appeal;
• Installation of networks: integration of electrical, plumbing, and HVAC systems.

1.3.3. Shipping Container Specifications and Definitions

The semi-basement floor is semi-buried, built with a reinforced concrete perimeter wall. The ground floor is made up of two 40-foot (40’HC) containers supported by the concrete walls of the semi-basement, and the first floor has two other SCs over the ground floor (Figure 5).

The containers according to ISO 1496-1:2013 Serie 1 (1AAA) [28] are made of trapezoidal sheets with vertical ribs and dimensions as indicated in

Table 1. Geometry characteristics of containers 40’ HC.

	Length (m)	Width (m)	High (m)
Internal	12.192	2.438	2.896
External	12.032	2.352	2.698

.

The front panel and side walls are made up of steel sheets fully vertically corrugated into the trapezium section, butt-jointed together to form one panel by means of automatic MAG welding. The thickness of the panels is variable, having 2.0 mm thick panels for the front and outer side walls and 1.6 mm thick panels for the inner side walls. The plywood is marine grade, the top surface and the edges are coated with an 80 waterborne polyurethane coating of 80μ, and the bottom surface is coated with bitumen.

The roof is composed of a trapezoidal sheet with 2.00 mm thick steel ribs and with a certain upward camber at the centre of each trough and corrugation, these sheets being butt-jointed together to form one panel by automatic welding. The resulting sheet is supported by two top side rails on the side walls.

As the sheets are trapezoidal, they exhibit higher rigidity in the vertical direction (orthotropic sheet). Due to this configuration, they have the following load capacity as defined in

Table 2. Load capacity of the containers 40’ HC.

Self-Weight (kg)	Total (kg)	Surface (kg/m2)	V. Capacity (m3)
2300	36,000	1229.51	76.10

.

The container is airtight, the corrugated panels are welded by CO₂ shielded arc welding, the wooden floor is fixed to the cross members by self-tapping screws, and all crevices are sealed with elastic sealing compound. There are two ventilators with EPDM seal gaskets on each side wall and at each end.

The steel is Corten primed with a zinc-rich epoxy primer paint at 10–15 microns prior to assembly. After assembly, the external surface is coated with an epoxy primer and an acrylic topcoat, and the internal surface is coated with an epoxy high build coat.

2. Materials and Methods

This study presents the technical and constructive methodologies employed to transform ISO (40’HC) SCs into habitable architectural units, demonstrated through a residential project in Spain. The methodology integrates modular coordination, refurbishment processes, structural reinforcement, and thermal envelope optimization to achieve sustainable and compliant residential architecture.

Standardized SCs served as modular units, enabling spatial flexibility through aggregation, subtraction, and vertical stacking. The containers’ dimensions facilitated streamlined planning and construction integration and allowed efficient spatial distribution accommodating diverse typologies of areas adaptable to occupant needs.

A controlled refurbishment process was implemented to comply with building performance standards. Thermal and acoustic insulation was installed to reduce thermal bridging, enhancing occupant comfort. Surface treatments involving corrosion-resistant coatings were applied on marine-grade plywood flooring. Utility systems, including electrical wiring, plumbing, and HVAC installations, were fully integrated.

2.1. Structural Analysis

Structural behaviour was evaluated through simulations analysing load distribution, buckling, and joint optimization, following Eurocode 3 and National standards. The four container base corners were fixed to replicate real support conditions, and structural reinforcements included cross and longitudinal beams to compensate for wall removals, columns for vertical stacking and staircase support, and beams replacing original roof sheeting.

Structural modifications were made by introducing rolled steel sections. The connections between these elements and with the containers are hinges so that the behaviour of the structure is isostatic. Support reactions and internal forces (axial forces, shear forces, and bending moments) were obtained using static equilibrium equations.

2.1.1. Loads

Loads were estimated according to the CTE DB SE-AE standard [29]. These were classified into dead loads (self-weight), live loads (use and maintenance), and environmental loads (wind and snow).

Dead loads were estimated based on the self-weights of the structural and envelope elements, as follows:

• Density of steel: 78.50 kN/m³
• Plywood: 0.22 kN/m²
• Roof sandwich panel: 0.13 kN/m²
• Corrugated metal sheet: 0.05 kN/m²

A residential live load of 2 kN/m² was applied in the ground and first floor, and a snow load of 0.8 kN/m² was applied in the roof.

The actions of the wind were not considered due to the protected location of the house within the urban complex.

2.1.2. Limit States

The Ultimate Limit State (strength) of the steel was verified by determining the ratio of stress to the ultimate limit values according to the mechanical properties of the steel (S-275JR).

The Serviceability Limit State (deformation) was verified by determining the ratio of strain to the limits established in the CTE DB SE standard [30]. Maximum deflections were as follows:

• Ground and first floor beams, s/500 (where s is the span of the beam).
• Roof elements, s/250.

2.2. Thermal Behaviour Analysis

To counteract steel’s high thermal conductivity and improve energy efficiency, a ventilated façade system was installed with exterior and interior insulation, as well as with insulated suspended ceilings. The roof utilized sandwich panels supported by steel trusses and integrating concealed rainwater drainage.

Thermal transmittance values (U-values) were calculated by considering the thermal resistance (R-value) of each material layer in a building element. The total thermal resistance (Rt) is the sum of the R-values of all layers, calculated according to Spanish Building Code requirements [31] for opaque façades, windows, roof, and ground floor slabs demonstrating effective thermal resistance. Internal drywall framing facilitated mechanical, electrical, and plumbing system integration alongside insulation. Ceilings featured metal-framed plasterboard with insulation in occupied floors and the semi-basement. Flooring comprised laminated anti-impact sheets in living areas and ceramic tiles with waterproofing membranes in bathrooms. Openings were precision-cut without additional structural reinforcement due to their limited size.

The evaluation of the building’s energy performance was conducted using dynamic simulation modelling to quantify annual heating, cooling, and total energy demand, as well as overall consumption. The procedure followed the principles set out in Directive 2002/91/EC of the European Parliament, ensuring compliance with European energy performance certification requirements.

The software tool CE3X (version 2.3) was employed for the analysis. This application enables three-dimensional modelling of building geometry under site-specific climatic conditions, allowing for comparative assessment of alternative design configurations and the selection of the most energy-efficient solutions in accordance with recognized building energy modelling practices.

2.3. Accoustic Behaviour Analysis

Field tests were performed in accordance with the ISO 16283:2016 [32] series to ensure consistent and reliable evaluation of the building’s acoustic performance under real-use conditions. The following sections provide the specific configurations, instrumentation, and analysis procedures applied for each measurement type.

Airborne sound insulation measurements were carried out on the façade of the two rectangular rooms with window openings located on the first floor. In addition, impact sound insulation measurements were performed between the upper floor and the ground floor. The building envelope’s sound insulation targeted the minimization of external noise immission, with particular attention to the façade openings, which typically represent the weakest acoustic points. A ventilated façade system was employed for the blind sections, combined with Class 4 aluminium-framed tilt-and-turn windows for openings, optimized to maximize sealing at joints to prevent sound leakage. Single-Number Quantities (SNQs) for airborne sound insulation and impact noise were calculated according to standards.

2.3.1. Airborne Sound Insulation Measurement of the Façade

Airborne sound insulation measurements were conducted on the facades of two first-floor rooms, ROOM1 and ROOM2, both featuring exterior windows, using the global loudspeaker method specified in ISO 162833:2016 [33]. The procedure is valid for enclosure volumes ranging from 10 to 250 m³. The measurement frequency range considered has been 100 and 5000 Hz (i.e., the extended range for high frequencies, as considered in ISO 162833:2016 [33].

The following equipment was used for the measurements:

• a Brüel & Kjaer Type 4224 directional sound source placed at a minimum distance of 7 m from the centre of the façade, as specified in the standard, forming an angle of incidence of 45° to generate noise between 100 Hz and 5000 Hz;
• a Brüel & Kjaer Type 2270 sound analyser, whose calibration was checked at the beginning and end of the measurement using a Brüel & Kjaer Type 4231 calibrator (Hottinger Brüel & Kjaer GmbH, 64293 Darmstadt. Germany);
• a Brüel & Kjaer omnidirectional source Type 4196 for the measurements of reverberation time using the interrupted noise method according to ISO 3382-2:2008 [34].

As a result of the measurements, the standardised level difference, D_ls,2m,nT in third-octave bands, was obtained. This level difference is obtained by measuring the sound pressure levels outside the dwellings and at 2 m from the facade L₁ (dB), the sound pressure level in the receiving room L₂ (dB) and the reverberation time T (s).

The average sound pressure level L₂ within the enclosure has been calculated as the energy average of the sound pressure level measurements at five positions distributed within the maximum available space in the enclosure and determined by taking into account the limiting distances between the microphone positions and the walls as specified by the applicable ISO standard. Measurements were carried out with a microphone fixed on a tripod and without anyone inside the receiving room. To check whether the measurements were influenced by other sources of noise, the background noise was measured before and after the measurement of the sound pressure level at each of the measurement points in the room, to obtain a highly correlated characterisation of the background noise with that existing during the measurement at each of the points.

As previously mentioned, measurement of the average level of outdoor sound pressure L₁ in the vicinity of the façade was made placing the microphone at a distance of 2 m from the centre of the façade and at a height corresponding to that of 1.5 m above the floor of the receiving room, as shown in Figure 6.

For the measurement of the reverberation time, three microphone positions were chosen within the room, and two decays were measured at each position, giving a total of six decays of reverberation time in each room. The reverberation time T was calculated as the average of the time measured in the six measurements.

2.3.2. Impact Sound Insulation Measurement

Impact sound insulation measurements of the separation floor slab between the ground floor and the first floor were carried out using ROOM 2 as the emitting room and the ground floor, where the living room and kitchen of the dwelling are located, as the receiving room. Measurements were carried out according to the specifications of ISO 162832:2016 [35].

A standardised Brüel & Kjaer Type 3207 five-hammer impact machine was used for noise generation.

The standardised impact sound pressure level L_′nT in third-octave bands was calculated from the measured sound pressure level L_i and the reverberation time T in the receiving room.

For the calculation of the energetically averaged L_i in the receiving enclosure, four positions of the impact machine in the emitting enclosure were used, distributed in the available space, and fixed, considering that the minimum distance between the different positions and the enclosure boundaries should be 0.5 m. In each position, the machine was arranged at an angle of 45° (degree) to the direction of the ribs or beams of the floor slab. Four fixed microphone positions were fixed in the receiving enclosure using a tripod with a minimum distance of 0.7 m between positions and 0.5 m between each position and the enclosure boundaries. The sound pressure level was measured between 100 and 5000 Hz at two randomly chosen microphone positions for each of the source positions. A background noise measurement was taken at each of the measurement points before the transmitted level was measured. Impact noise levels were taken about two minutes after the impact machine was left running to stabilise the excitation. Reverberation time was measured in the receiving enclosure using the interrupted noise method with an omnidirectional Brüel & Kjaer Type 4196 source according to ISO 3382-2:2008 [34] and as an average of six measurements in the manner described in the measurement of airborne sound insulation of the facades.

The contribution of airborne noise produced by the impact machine was evaluated, and measurements were taken to verify that the influence of airborne noise produced by the impact machine was negligible. The process followed is as indicated in Annex D (section D.6) of the standard ISO 16283:2016 [32].

2.3.3. Single-Number Quantities (SNQs)

Based on the measurement of sound insulation in one-third octaves, the global magnitudes that characterise the acoustic performance of the construction elements were calculated according to the procedure specified in the standards ISO 717-1:2020 [36] and ISO 717-2:2020 [37], respectively.

The The airborne sound insulation SNQs were calculated as follows:

• Normalised weighted level difference of elements D_ls,2m,nT,w (C; C_tr), where C and C_tr are the spectral adaptation terms used to characterize sound insulation with respect to pink noise and traffic noise as the sum of this spectral adaptation term and the global magnitude. As indicated in Annex A of ISO 717-1:2020 [36], C is the general magnitude correction term used for those sound sources characterised by the scarcity of low frequencies (e.g., voice, radio…). The SNQ corrected with this term must be used when choosing a separating construction element between dwellings. On the other hand, C_tr is the correction term that gives special relevance to sound sources with prominent low frequencies (e.g., urban road traffic, trains at low speeds, certain industrial activities…) so that the SNQ corrected with this term will be used for the choice of façade elements.
• A-weighted standardized level difference D_2m,nT,A in façades for pink noise as an overall index in dBA in the case where the dominant noise is conversations, music, etc. In general, it is verified that D_2m,nT,A = D_2m,nT,w + C.
• A-weighted standardized level difference D_2m,nT,Atr on façades for car noise as an overall index in dBA in the case where the dominant exterior noise is car noise. In general, D_2m,nT,Atr = D_2m,nT,w + C_tr.

In the case of impact sound insulation for floor slabs, the standardized weighted impact sound pressure level L^′_nT,w has been calculated as the SNQ for impact sound insulation between rooms in buildings.

3. Results and Discussion

3.1. Structural Analysis and Performance Modifications

Shipping containers are engineered to withstand extreme loads during transport, a feature that makes them particularly attractive as structural elements in building projects. Their robust construction, which includes steel trapezoidal sheets and cold-formed steel profiles, provides a high degree of mechanical strength and durability [38].

However, the use of these containers as load-bearing modules in buildings presents new challenges due to the uncertainty of some material properties. The literature has shown that it is important to evaluate the structural behaviour of shipping container buildings and how these modules will react under various loads and conditions.

The following items are important to consider:

• Accurate simulation of load distributions: prediction of stress concentrations and identification of potential structural weaknesses;
• Optimisation of connections and joints: ensuring that the assembly of multiple containers results in a stable, integrated structure;
• Enhancements in durability and safety: considering changes in decisions regarding necessary reinforcements and design modifications to increase the lifespan of the building structure;
• Structural strengthening: involves reinforcing the container to enhance its load-bearing capacity, including additional support for door frames and corners.

For the support conditions, it was assumed that all translations in the four lower corners were restricted, because containers are designed to be supported by the corner pieces.

The global results show that containers have rigid behaviour. This behaviour can be explained by the continuous connection between many of the elements of the container. [38].

To verify the safety of the structural elements of the containers, structural calculations must follow the structural codes that govern the design of the structures. In this case, for steel structures and for European space, Eurocode 3 should be used. For general steel elements, Part 1-1 [39] should be used, for the commercial cold formed section, Part 1-3 [40] should be used, and for non-commercial cold formed sections, Part 1-5 [41] should be used.

Cross beams are the most heavily loaded reinforcements, with a stress level of 24% and a deflection of span/509.

The foundation wall is anchored with steel dowels (Ø12-0.15 mm) on shallow stripe foundations on stable soil of adequate bearing capacity transferring building loads directly to the supporting soil by vertical pressure. A HEB220 beam was positioned over the basement vehicle access opening to support the corners of the containers.

The SCs of the ground floor were supported along the exterior perimeter of the two containers on the cast-in-place concrete basement wall (250 mm) and to support and avoid the buckling deformation mentioned above; also aggravated by the elimination of the inner side walls, a couple of HEB 240 profile cross beams were positioned at the distances of 3.75 m and 3.22 m, welded to steel base plates (250 mm × 250 mm × 10 mm) casted into the concrete walls. The positions of those beams were determined by the voids of the staircase.

Along the eliminated inner side walls, HEB 100 profiles were introduced, as longitudinal beams on both levels, supported by the previously mentioned cross beams on the ground floor, by IPE 180 and IPE 220, and also on HEB 100 columns on the first floor (Figure 7). The positions of cross beams are usually on one-third of the longitudinal axis, but in this case, it was changed and adapted to the void of the staircase.

The most challenging aspect of the structural adaptation of the container was supporting the beams directly on the container walls. Specifically, the beams transferring the greatest load to the wall were those forming the stairwell opening, with a maximum point load (factored by the load combination) of 33.1 kN. Additionally, the beam support was executed in such a way that the load was transferred onto a full corrugation of the wall, as shown in Figure 8.

The wall material was JIS 3125/2010 grade steel with a yield strength of 345 MPa. The wall had a thickness of 2 mm and a height of 2.63 m. Considering a material safety factor of 1.05 and assuming that the wall behaved in compression as a pinned-pinned column, the maximum load it could resist was calculated in accordance with EN 1993 [40].

The geometric properties of the section were as follows: an effective cross-sectional area of 735 mm², a moment of inertia about the weak axis of 162,700 mm⁴, and a reduced slenderness ratio of 2.226. Based on these values, a buckling reduction factor of 0.186 was obtained, resulting in a maximum admissible support load of 44.92 kN.

As previously mentioned, the applied load was 33.1 kN, meaning that up to 74% of the wall’s load-bearing capacity was utilized in compression.

The vertical connection of the SCs was made by welding the corner connections of the containers. In addition, columns (HEB 100) were placed to support the stairs in the corner of the void formed by IPE 180 on the ground floor and HEB 100 on the first floor (Figure 9). The distribution of the house required the removal of one of the inner side walls of the containers. Cross IPE beams and felled HEB pillars were used to reinforce SCs before removing side walls and floor beams (Figure 10).

The original container height was 289 cm. After removal of the original roof panels and installation of structural reinforcements, the clear internal height beneath the primary beams was reduced to 241 cm. A suspended ceiling was subsequently installed at 250 cm, with localized drops around structural beams resulting in a minimum free height of 235 cm at those points.

The roof has little structural significance, so the steel sheets from the roof were removed, and the new roof structure was made of sloping joist steel tubes (100.50.3 mm) over steel beams (IPE 200) welded to the side rails (Figure 9).

The hinged doors were removed to mount windows in the rear end.

Openings were cut into the sides and the front container to allow for windows and doors. The small size of the openings made it unnecessary to use reinforcements in steel sheets.

3.2. Thermal Performance

To enhance the thermal performance and energy efficiency of shipping container building envelopes, a widely adopted strategy involves the integration of additional insulation layers. This retrofit not only minimizes heat transfer but also contributes significantly to indoor thermal comfort and overall building sustainability, incorporating high-performance insulation materials in the interior and exterior faces of the envelopes and at same time guaranteeing fire safety conditions for exterior layers. Furthermore, thermal anomalies such as thermal bridges, air infiltration points, and excessive solar heat gain through fenestration systems need to be addressed, as well as moisture resistance and vapor permeability, especially in hot and humid climatic zones.

These evaluations allow for a more targeted and effective retrofit design, ensuring that thermal weaknesses are identified and mitigated. Such diagnostic insights are particularly critical given the thin, conductive steel structure of SCs, which can rapidly transfer heat without adequate insulation.

The thermal insulation system consists of two layers: the first positioned on the inner side of the container wall and the second on the exterior. The inner layer, installed within the internal lining that houses building services, aligns the insulation plane with the window frames and mitigates thermal bridging in their vicinity. The outer layer, placed within the ventilated façade assembly, forms a continuous thermal envelope that eliminates thermal bridges at the junctions between containers.

3.2.1. Building Envelope

A ventilated metallic façade was set up on the exterior envelopes of the SCs. The structure consists of brackets screwed to SC steel sheets and vertical aluminium T-shaped girt profiles. The exterior cladding is a horizontal wave rolled corrugated lacquered galvanised steel sheet; the exterior insulation panel is made of 70 mm thick polyisocyanurate (PIR) rigid boards. Between the exterior cladding and the insulation material, an air circulation system is established that allows the removal of heat and humidity from the interior wall and disperses them to the outside (Figure 11).

The characteristics of the entire envelope materials are detailed in

Table 3. Characteristics of the envelope materials.

Material Name	Thickness (mm)	U Value (W/m2·K)
Plywood	28	0.10
Gypsum board	15.9	1.30
Rockwool	60	0.033
PIR	70	0.022
Steel	0.6	50.20

, and transmittance U (W/m²·K) for the envelope systems of the stack house and the values required by the National Building Code are detailed in

Table 4. Transmittance U (W/m²·K) for the envelope of the stack house (SH) and the minimum required by the National Building Code (CTE).

	Opaque Facade	Glass Windows	Roof	Ground Floor Slab
SH	0.18	2.4	0.184	0.28
NBC	0.66	2.5	0.38	0.49

.

The ground floor consists of a 28 mm plywood board, a double 50 mm rock wool panel, and a laminated plasterboard.

The roof is a 60 mm thick sandwich metallic panel with a PIR core slopped on triangular steel beams as trusses with a hidden aluminium rain gutter on the sides (Figure 12 and Figure 13).

3.2.2. Wall Systems and Finishing Works

The infill system is very similar to that of a standard home. Interior wall cladding is a drywall framing system that forms a cavity to locate internal insulation and components of mechanical, electrical, and plumbing systems (Figure 14).

The rooms are separated with an internal steel frame system.

All suspended ceilings are metal frame plasterboard ceilings; the first floor and semi-basement ceilings are fitted with insulation (Figure 14).

Laminated flooring with anti-impact sheets was used in the bedrooms, living room, and halls. The bathroom floor was made of ceramic tiles installed on a polyethylene membrane glued to plywood.

3.2.3. Windows Systems

The window frames are made of aluminium with thermal bridge breaking and a 70 mm concealed leaf.

The glazing system is composed of an outer laminated 4 + 4 mm glass panel with a 12 mm air cavity and an inner laminated 3 + 3 mm glass panel.

The windows have a blackout system based on motorised extruded aluminium roller blinds with a PVC monoblock shutter box (Figure 15).

3.3. Energy Simulation

The building is equipped with a high-efficiency air-to-water heat pump providing both underfloor heating and cooling, with a Coefficient of Performance (COP) of 4. Simulation parameters included indoor operative temperature setpoints of 20–22 °C (winter) and 25–26 °C (summer), in alignment with ASHRAE Standard 55 thermal comfort guidelines.

Table 5. Energy simulation results.

Energy Efficiency Variables	Value
Consumption of non-renewable primary energy	34 kWh/m2 year
Carbon dioxide emissions	6.1 kgCO2/m2 year
Heating demand	40.2 kWh/m2 year
Cooling demand	7.9 kWh/m2 year

summarises the resulting energy efficiency indicators from the simulation output. Based on these results, the dwelling achieves an Energy Performance Certificate (EPC) rating of “A”.

3.4. Strategies for Container Adaptation to Different Climates and Uses

The present study focuses on the specific climatic conditions of Southwest Europe, characterised by a continentalised Mediterranean climate with cold winters and warm, dry summers. According to the Köppen classification, Madrid lies in a transitional zone between the cold temperate semi-arid climate and the Mediterranean climate. While the results are specific to this context, it is essential to examine how the findings could be adapted to other climatic regions.

In colder climates, container housing may require advanced insulation systems and highly efficient heating solutions to maintain indoor comfort. In Nordic countries, for example, triple-glazed windows, high-performance thermal insulation materials, and the integration of passive solar heating strategies are likely to be more effective. In hot climates, the primary focus should be on reducing cooling loads through measures such as reflective roofing materials, external shading devices, ventilated cladding façade systems, and enhanced natural ventilation to mitigate overheating.

Certain design principles—such as maximizing natural cross-ventilation, incorporating vapor barriers in the building envelope (particularly in humid climates), and optimising window-to-wall ratios—can be universally applied to enhance energy efficiency. However, comprehensive studies are required for specific climatic contexts, including arid, cold, and tropical regions, to fully make use of the adaptability of container-based housing in maintaining both energy efficiency and thermal comfort.

Orientation also plays a critical role in energy performance. In the northern hemisphere, a southern orientation is generally the most suitable for maximizing energy savings in residential buildings. In various regions of Spain, this orientation has been shown to be optimal for the main façade. In some cases, particularly when advanced insulation technologies such as structural insulated panels are employed, a western orientation may also prove advantageous. However, in scenarios without insulation, an eastern orientation—closely followed by southern—may yield the lowest energy consumption.

The reuse of decommissioned shipping containers represents an effective strategy for addressing environmental, social, and economic challenges by integrating container reuse into the principles of the circular economy.

Future work should include comparative assessments of the sustainability performance of standardised container-based housing versus conventional construction systems.

Further research directions should involve performing more detailed, long-term simulations to achieve greater precision in predicting energy performance, and using meteorological datasets based on climate projections to analyse building behavior under anticipated future climatic conditions throughout its service life.

3.5. Acoustic Performance

The building envelope is responsible for protecting the interior of the building from outdoor noise. This envelope includes the façade and roofs, as well as the slabs that are in contact with the exterior. In façades, sound insulation is determined mainly by the weakest or least sound insulating construction element, which is usually the window. In this sense, the façade, in addition to the thermal protection, watertightness, or fire resistance requirements, must meet minimum acoustic requirements to ensure that the incoming noise is below the limits determined by the applicable regulations. These requirements are given according to the noise outside the room. Optimisation of sound insulation has been pursued with the ventilated façade, for the blind part, and with a Class 4 window for the opening enclosure as described in the previous section. In addition, special attention has been paid to maximising the insulation between the union of both parties. To test the effectiveness of the actions, airborne sound insulation measurements were carried out on the façade of the two rectangular rooms on the first floor.

In addition, insulation measurements were performed of impact noise between the upper floor and the ground floor. Although measurements of sound insulation of impact noise are always important in construction, they are even more important in constructions such as the stack house project, since the separating slab has very different characteristics from those usually used in traditional construction.

The volumes of the measured spaces, ROOM 1 and ROOM 2, are 25.7 and 26.8 m³, respectively, with an opening area of 160 × 215 cm² in both cases (see Figure 4). The rooms were furnished. The façade opening consisted of an aluminium framed tilt-and-turn window with a single-number quantity Rw (C, C_tr) of 38 (−1, −4) and a critical frequency for which the insulation of this configuration is reduced at 2000 Hz.

Figure 15 shows the standardised level difference, D_ls,2m,nT, in the third-octave bands for the two measured façades. Sound insulation always depends on the frequency and increases progressively, following the usual behaviour based on the laws of physics.

The insulation curves measured for ROOM 1 and ROOM 2 show a loss of insulation corresponding to the critical frequencies. In the vicinity of these coincidence and/or critical frequencies, the façade displays very little resistance to sound transmission and suffers a significant loss of its insulating capacity.

From an acoustic point of view, the blind part does not behave like a multi-leaf system, as they are connected at some points by the slab or by the configuration of the window opening. Insulation drops at around 800 Hz could be linked to the critical frequency of the 70 mm ribbed steel sheet that constitutes the ventilated façade, while the drop at around 2000 Hz is subject to the critical frequency described by the glass manufacturer based on laboratory measurements. The decrease in insulation between approximately 2000 and 4000 Hz could correspond to the critical frequencies, at about 2600 Hz, of the 13 mm thick plasterboard used in the interior cladding of the façade and the critical frequency of the 2 mm steel container wall around 4000 Hz.

Figure 16 also includes the sound reduction index measured in the laboratory with a window of the same class and the same glazing. Considering the class of window used, the type of glazing and its dimensions are the most important factors determining sound insulation. This would explain the lower insulation measured at low and high frequencies in ROOM 1, which has a larger opening area. It should also be taken into account that for the insulation difference measured below 250 Hz—lower than the cut-off frequency or Schroeder frequency (280 Hz)—the sound field is not diffuse, and the measured sound pressure level is greatly affected by the chosen positions and the specific modal configuration of the enclosure.

However, in addition to the size of the opening, it is very important in the case of the façade that the joints between the façade opening and the window frame are properly sealed and that the connections with the rest of the elements are correctly executed. In addition to the direct transmission path through the separating element, sound is also transmitted indirectly through the joints of the different parts that make up the façade; that is, it also depends on the airtightness of the enclosure. The façade is not structurally independent of the slab and the separating partitions, so acoustic transmissions are also induced through these connections by the vibration of these elements until they reach the receiving enclosure, where they are converted into airborne noise. Indirect transmissions in façades are usually smaller than between enclosures, but when façade elements are connected to enclosure elements, it must be considered that the insulation values on site will be lower than those obtained in the laboratory.

In Figure 17, the standardised impact sound pressure level L′_nT has been plotted in third-octave bands. As already mentioned, it is interesting to have an estimate of the insulation of the slab to assess its suitability for blocks of flats with containers. The results indicate how the joint execution of a floating floor and a suspended ceiling generates levels of insulation to impact noise. The increase in impact noise level of approximately 3150 Hz could be associated with the contact between the horizontal element and the ventilated façade.

The descriptors D_ls,2m,nT,w and D_2m,nT,Atr are currently adopted by some European countries’ regulations to define the legal requirements of façade insulation [42].

In Spain, National Building Code (CTE) [43] specifies the SNQs used to express sound insulation and their limit values. The A-weighted standardised level difference in façades and roofs for traffic-dominant outdoor noise, D_2m,nT,Atr in dBA, is the general indicator used to describe the sound insulation between an enclosure and the outside. The frequency range considered for the calculation is 100 to 5000 Hz.

Table 6. Global magnitudes of airborne sound insulation of the facade and spectral adaptation terms in the two enclosures on the first floor of the residence.

	ROOM 1	ROOM 2
Dls,2m,nT,w (C; Ctr) (dB)	36 (−2; −4)	35 (−2; −5)
D2m,nT,A(dBA)	35	34
D2m,nT,Atr(dBA)	32	30

shows the global airborne sound insulation values for the two façades and the spectral adaptation terms.

One of the central elements for determining the sound quality of homes is the insulation against outdoor noise. The main strategy to limit noise within buildings is sound insulation of the façade.

The requirements for outdoor sound insulation are established in the CTE [43] depending on the level of noise in the home, as in most European countries. Outdoor noise levels are calculated based on traffic data and conditions. Traffic noise levels are often available from the authorities.

The stack house is located in an urban area with reduced traffic, not directly exposed to noise from cars or industrial activities. Therefore, external noise levels are lower than 60 dBA. At this level of noise, the regulation requires a minimum sound insulation of 30 dBA. Table 5 shows how the adopted solution guarantees compliance with the sound insulation requirements.

In terms of impact sound insulation, a value for the global impact sound pressure level L^′_nTw of 58 dB, the preferred basic descriptor in European Regulations, is calculated from the measurement for the floor slab of the container dwelling. Although not applicable in this case, the CTE [43] indicates that horizontal separation of construction elements between the different units of use will have characteristics such that L^′_nTw is not greater than 65 dB.

In summary, with a façade surface mass of around 100 kg/m² and an intermediate floor of approximately 50 kg/m²—well below the 250–350 kg/m² typical of concrete or masonry—the adopted construction system still achieved the airborne and impact sound insulation requirements set out in the CTE [43] for urban areas. The glazing proved to be the most acoustically vulnerable component of the façade, confirming the common occurrence that windows are typically the weakest element in the building envelope. The measured impact sound level of L^′_nTw = 58 dB confirms the effectiveness of the floating floor with MDF board and resilient sheet combined with a suspended ceiling, a solution consistent with recommendations for lightweight modular systems [2]. Overall, the results suggest that the inherent structural configuration of the container—together with multilayer treatments— can help limit indirect transmission paths, providing acoustic performance levels that support the feasibility of container-based housing as a regulatory-compliant building solution.

4. Conclusions

The transformation of shipping containers into habitable dwellings offers a promising alternative to traditional construction, particularly in terms of sustainability, modularity, and cost-efficiency. The presented case study demonstrates that with adequate structural reinforcements and precise design interventions, modified ISO 40’HC containers can meet residential performance standards. Structural evaluations, based on national and international codes, confirmed the mechanical viability of altered container assemblies when reinforced with steel beams and columns.

According to the calculations performed, which considered both the amplification of loads due to the most unfavorable load combination and the reduction in resistance due to the material safety factor, the maximum point load that the container wall can support is 44.92 kN.

Thermal comfort was significantly enhanced through a dual-insulation approach, rigid PIR foam externally and mineral wool internally, complemented by ventilated cladding façades system and sandwich panel roofing. These upgrades ensured compliance with National Building Code requirements for energy efficiency.

Likewise, compliance with the basic noise protection conditions required in the regulations of the different countries is achieved by using construction systems whose sound insulation values are higher than those demanded in the regulations.

Traditional construction systems have been extensively tested in the past; however, the enclosures and floor slabs built from the modification of shipping containers are incipient, and their sound insulation properties are not deeply investigated.

In this research, a characterisation of the acoustical properties of the construction systems of a single-family house built by modification of shipping containers has been carried out. It is our intention that these results can help designers of houses built with shipping containers in the future by offering an estimate of the sound insulation properties of these envelope solutions and horizontal separation elements between dwellings.

Despite the relatively low surface mass of the façade (≈100 kg/m²) and intermediate floor (≈50 kg/m²) —well below the 250–350 kg/m² typical of concrete or masonry— the adopted envelope and floor assemblies achieved the sound insulation values required by regulation for low-noise urban areas. The glazing was identified as the weakest element, consistent with trends observed in other lightweight façade systems. The measured impact sound level (L^′_nTw = 58 dB) confirms the effectiveness of the floating floor with MDF board and resilient underlay combined with a suspended ceiling, a configuration aligned with good practice for lightweight modular buildings where structural decoupling and added mass are crucial. These findings indicate that the inherent structural configuration of the container, together with multilayer treatments, can help limit indirect transmission paths and deliver acoustic performance levels that support the viability of container-based housing as a sustainable residential option.

Overall, the study concludes that while container-based construction presents inherent challenges—particularly in thermal, acoustics, and spatial limitations, these can be effectively mitigated through thoughtful engineering and design strategies. The resulting data contributes to the technical knowledge base necessary for architects and engineers aiming to integrate reused containers into mainstream residential construction, particularly under sustainability-driven frameworks.