Adaptation of Connection Systems for Integration with Engineered Wood Products in Buildings: A Systematic Review

Abstract

Connection systems are a critical component of buildings constructed with engineered wood products (EWPs), influencing structural integrity, durability, and construction efficiency. This systematic review categorises connection types into mechanical, adhesive, and interlocking systems and evaluates their structural performance, adaptability in prefabrication, applicable design standards, and modelling approaches. The review synthesises recent trends in EWP connection research, highlighting key developments in digital fabrication, reversible joints, and sustainable construction. Findings emphasise the need for standardisation, performance validation, and hybrid systems to support the wider adoption of prefabricated timber structures in environmentally responsible building practices.

1. Introduction

1.1. Background

Engineered Wood Products (EWPs) are prefabricated elements widely employed in various modern construction projects including multi-story mid-rise apartments, commercial developments, and public infrastructure [1,2]. EWPs are increasingly used as sustainable building materials for wall panels, floor panels, beams, and columns. Commonly used EWPs include Parallel Strand Lumber (PSL), Laminated Veneer Lumber (LVL), glulam, Oriented Strand Boards (OSBs), Cross-Laminated Timber (CLT), and Structural Insulating Panels (SIPs). EWPs offer several advantages over traditional sawn timber, including improved dimensional stability, the capacity to create larger structural components, reduced susceptibility to natural flaws, such as knots, increased durability and more consistent mechanical properties [3,4].

EWPs are particularly suited for prefabrication and hybrid construction. EWPs can be prefabricated into large panels or modular components with all necessary cutouts and suitable connection systems that allow for seamless assembly of elements on-site. Incorporating hybrid construction will minimise on-site operation time and construction costs while enabling construction even in extreme conditions [5]. Additionally, the controlled manufacturing process improves precision, reduces material waste, and ensures higher quality than that achieved with traditional on-site construction methods. Recent advances in machine vision have enabled automated detection of grading singularities, further improving the reliability of timber selection for engineered applications [6,7].

Effective connection design also plays a crucial role in ensuring construction efficiency as well-designed connections simplify on-site assembly, reduce labour requirements, and improve overall structural performance. Connections are the most critical components in any structural system as they influence the stability, strength, serviceability, and durability of the overall structure. According to Lopes et al. (2018), connection systems are a key aspect of a robust structure [8]. The performance of a connection depends not only on the structural capacity, but also on the deformation capacity [9] and other non-structural features such as the ability for disassembly and accessibility. Many of these EWPs are glue-bonded and, therefore, affected by fire. Moisture ingress into EWPs can lead to a reduction in structural integrity [10]. Hence, performance-based durability designs must consider moisture movement, thermal effects, and fire aspects during the detailing stage of connections. Beyond these considerations, the connection system must also perform effectively under varying environmental and loading conditions. In regions prone to seismic activity or strong winds, the connections must have the ability to withstand lateral forces.

Given these complexities, a thorough evaluation of different connection types is essential to optimise their application in prefabricated EWP buildings. Despite significant advancements in EWP connection technologies, several key research gaps remain. The existing studies primarily focused on mechanical, adhesive, and interlocking connections in isolation, with limited comparative research on their overall effectiveness in prefabricated EWP buildings. This review aims to bridge these gaps by systematically analysing recent research on connection types, their adaptability to prefabrication, and opportunities for standardisation and performance improvement. The objective is to assess advancements in connection technologies from 2005 to date critically and provide insights into optimising connection designs for prefabricated timber buildings, thereby contributing to future research and industry applications.

1.2. Classification of Connections in Buildings with EWPs

According to Lopes et al. (2018), four types of panel assemblies are used in EWPs [8].

• Panel-to-panel: connects adjacent panels through techniques such as tongue-and-groove, overlap joints, concealed fixings, and compressed seals, often forming self-supporting structures.
• Panel-to-structure: panels are fixed directly onto the primary structure to ensure load transfer and stability.
• Panel-to-subframe: uses intermediate elements such as mullions or transoms to support the panel.
• Panel-to-cladding: involves mounting cladding walls onto a carrier system or substrate wall often incorporating an air cavity.

Buildings with EWPs can be assembled using either the “platform” or “balloon” techniques. These techniques define the load paths and influence the selection of connection types. In the platform approach, vertical walls are intermittently discontinued at each level by horizontal panels, forming a “sandwich” structure with two consecutive vertical panels. In the balloon technique, vertical walls remain continuous throughout the height of the building while the floors are internally linked to the walls through a dedicated connection device [11]. Platform framing with EWPs is generally simpler and less labour-intensive, making it a popular choice for residential and commercial buildings. Additionally, each floor can serve as a separate fire compartment, enhancing fire safety. Balloon construction is often selected for its potential structural advantages in taller buildings and its ability to create open interior spaces [11].

In modern EWP buildings, traditional panel assemblies are replaced by various configurations of metal fasteners and adhesives, which are essential for forming larger sections or connecting structural members. EWP connections can also be classified into moment connections, shear connections, and axial connections based on load transfer mechanisms, similar to the classification used in steel connections. However, the classification presented in Figure 1, Figure 2 and Figure 3 offers a more effective approach for analysing EWP buildings as it integrates practical application (Figure 1), structural behaviour (Figure 2), and material compatibility (Figure 3). Additionally, this classification aligns with existing structural design codes and research methodologies, ensuring its relevance for both industry applications and academic studies.

1.3. Design Methods and Standards

Structural design codes aim to provide simplified yet reliable guidelines for practitioners. The design of timber connections is generally regulated by structural standards that incorporate semi-probabilistic safety concepts. Load and Resistance Factor Design (LRFD) methods are adopted in the US, Canadian, European, and Australian codes [9], where both load and resistance are subject to uncertainties. However, current codes of practice do not fully address the wide variety of connections used in timber structures, especially those involving EWPs, and require more specific provisions for connection design.

According to a survey conducted on Eurocode 5, connections consistently ranked as the most challenging aspect, often requiring excessive design effort, leading to gaps in the provided information and resulting in inefficient or costly construction. Respondents identified several key issues, including ambiguous provisions, incomplete solutions, and errors in the code, which complicate its practical application. These concerns highlight the need for improved clarity and more comprehensive guidance within design codes related to connections [12].

In the absence of clear design standards, experimental methods and numerical simulations offer valuable insights. During the design phase, experimental analysis may be conducted to obtain relevant parameters. Generally, the strength and stiffness of a connection system are determined using a push-out test, which provides a load slip relationship under shear loading. The strength is quantified as the maximum load at failure, and stiffness is measured using the slip modulus at three different load levels, i.e., 40%, 60%, and 80% of the mean maximum load corresponding to service, ultimate, and near-collapse load levels [13,14]. Finite element modelling and other numerical simulations also allow for a better understanding of complex connection behaviour.

Proper connection design and detailing are essential in prefabrication as they ensure structural stability, ease of assembly, and compatibility between components while also reducing rework. Precise joints minimise on-site errors and improve manufacturing efficiency while meeting performance and durability standards. At an early stage of design, it is important to introduce proper jointing techniques that satisfy both architectural and budget requirements [15].

1.4. Modelling Approaches

Extensive experimental testing is time-consuming and costly. Finite element modelling (FEM) provides an efficient alternative for accurately predicting structural performance by utilising mechanical properties such as global stiffness, load-carrying capacity, and element interactions [16]. A well-developed FEM should define material properties, boundary conditions, loading conditions, and both elastic and post-damage phases up to failure. Several studies have validated FEMs by comparing connection strength and stiffness results obtained from push-out tests, which capture the load-slip response of connections under shear loads [17,18].

Stochastic Finite Element Method (SFEM) enhances the reliability of EWP structural analyses by incorporating material variability and uncertainties, leading to more precise structural behaviour predictions [19]. Time-dependent behaviour is a crucial consideration in the FEM of EWP structures. Factors such as creep, moisture-dependent Young’s modulus, shrinkage and swelling, and thermal expansion must be incorporated to capture the long-term performance of timber connections accurately. Advanced FEMs integrate moisture variations, temperature fluctuations, and sustained loading conditions into expanded material formulations, enabling more realistic simulations [20].

Recent advancements in FEM have significantly improved the ability to simulate the complex behaviours of EWP connections. High-fidelity modelling approaches, such as continuum damage mechanics, enable more accurate prediction of dynamic responses and failure mechanisms under varying loading conditions [21].

FEM software such as ABAQUS, ANSYS, SAP2000, and RFEM is widely used for analysing timber connections. Newer versions of ABAQUS are preferred for their advanced material modelling capabilities, making them effective for simulating fire performance and dynamic loading conditions [21]. Additionally, ABAQUS is employed for modelling moisture-dependent behaviour, allowing for the simulation of stress redistribution in timber under varying humidity conditions. It is also used to analyse long-term creep effects in timber structures [22], ensuring accurate long-term serviceability predictions. Furthermore, the software facilitates complex joint modelling by capturing contact interactions and nonlinear behaviour in dowel-type connections [21].

Beyond FEM, recent computational advancements including machine learning-based predictive models and Artificial Intelligence (AI) are transforming the accuracy and efficiency of connection design [23,24]. These tools enable data-driven optimisation, reducing reliance on physical testing while improving design outcomes. Furthermore, Building Information Modelling (BIM) frameworks now incorporate FEM data [25], enhancing digital workflows and optimising the prefabrication of timber structures.

2. Types of Connections and Their Performance

2.1. Mechanical Connections

Mechanical fasteners can be metallic, plastic, or timber and are used to transfer loads between connecting elements. A wide variety of mechanical fasteners is available in the global market, and during selection, the designer must consider factors such as the load transfer mechanism, withdrawal capacity, yield moment capacity of the fastener, embedment strength of each timber member, and friction between the surfaces.

Mechanical connections used for timber–timber connections are primarily dowel-type. A typical dowel-type connection includes nails, staples, bolts, and wooden dowels. These connections are essential in prefabricated elements as well as for on-site assembly. A substantial amount of research has been carried out on the geometric positioning of dowels and corresponding failure modes. Yurrita and Cabrero (2021) emphasise the importance of distinguishing between ductile and brittle failure modes in timber connections, highlighting how geometric parameters significantly influence these outcomes [26]. Eurocode 5 has adopted Johansen’s theory and equations to design dowel-type connections while also incorporating the rope effect to account for the frictional forces between the members [13].

Self-tapping screws are widely adopted in timber construction as fastening and reinforcing methods to prevent split failure as they allow for a wide range of geometrical configurations with increased stiffness and capacity, especially when utilised in inclined configurations relative to the grain [16]. According to the experimental results of Schiro et al. (2018), double-threaded screws exhibited higher values of stiffness compared to single-threaded screws despite their small diameter, while screw joints demonstrated higher connection capacity values with hardwood than with softwood [27]. Schiro et al. (2018) also analysed the shear–torsion configuration of different screw angles in timber-to-timber connections and concluded that a screw inclined at an angle of 45 degrees relative to the grain is stiffer and stronger than those at a 90-degree angle. Inclined screws allow for rationalisation and cost reduction in the design and installation of connections [27].

Abdoli et al. (2022) evaluated the screw and nail withdrawal strength properties in the transverse, radial, and tangential directions of CLT made from different types of hardwood and softwood [28]. Nails and screws show similar trends; however, in all test specimens, screws demonstrated a higher withdrawal capacity than nails.

Recent studies have continued to explore the structural performance of Compressed Wood (CW) dowels as sustainable alternatives to traditional steel fasteners in timber connections. A comprehensive review highlighted that double-shear tests demonstrated the ductility of compressed wood dowels to be greater than that of maple dowels and reasonably close to that of steel pins [29]. Additionally, Conway et al. (2021) investigated the reinforcement of timber elements in compression perpendicular to the grain using densified wood dowels, finding a 16% increase in compressive strength for reinforced specimens [30]. These findings underscore the potential of compressed wood dowels to enhance the ductility and strength of timber connections, offering a viable and sustainable alternative to metal fasteners. However, due to the differences in mechanical properties of CW, the mean performance of CW is less than that of steel dowels in terms of ultimate failure load, end stiffness, moment carrying capacity, and rotational stiffness. The current codes of practice should be upgraded to evaluate the performance of CW-based dowel connections [31].

Metal plates, especially gusset plates and connector plates, are predominantly used in splice joints and to transfer shear forces in the prefabrication of trusses and frames. Opting for the correct size of the metal plate not only conserves materials and reduces expenses, but also enhances the strength of the connection. The stress distribution of the nailed metal plate is not uniform due to the many holes in the section [32]. Recent studies confirm the effective use of metal plate connections with EWPs, highlighting their suitability for prefabricated timber systems. Key factors influencing performance include plate orientation, tooth density, and resistance to tooth withdrawal, all of which significantly affect joint strength and stiffness [33].

Composite construction involving concrete floors and timber beams is increasingly used in hybrid EWP buildings and bridges. Prefabrication methods can be applied by connecting the timber beam on-site to an off-site-manufactured concrete slab using embedded shear connections. As prefabrication prevents direct moisture contact between wet concrete and timber, it significantly reduces shrinkage compared to traditional wet-on-wet processes. Although the basic load transfer mechanism in timber–concrete dowel-type connections is similar to that in timber–timber connections, several differences exist. Lower deformation at the concrete interface promotes a more effective load transfer, resulting in higher collapse loads. Conversely, the brittle crushing behaviour of concrete can reduce transmission efficiency. An increased friction component in the load transfer mechanism limits deformability, while higher axial load-carrying capacity combined with low axial deformation enhances the rope effect [34].

Similar to timber–timber dowel joints, the failure behaviour and ultimate strength of timber–steel connections are significantly influenced by several factors. These include the embedment strength and compressive strength of the timber, whether parallel or perpendicular to the grain, the type and size of the fastener, and the loaded edge distance [35]. In steel–timber connections, fasteners can be either laterally loaded, axially loaded, or a combination of both, whereas timber–timber connections involve only laterally loaded conditions. Dorn et al. (2013) conducted compressive test series on timber–steel dowel connections to examine the effects of such test variables as slenderness, surface roughness, and end distance. The results confirmed the expected effects of surface roughness on connection behaviour, showing a significant increase in both maximum displacement and maximum load at failure, with the impact being more pronounced in dense wood than in softwood [36]. It is important to note that the roughening of dowels changes their failure mode from brittle to ductile. End distance reduces the maximum displacement without influencing the load–deflection curve behaviour.

2.2. Adhesive Connections

The mechanical performance of adhesives is strongly influenced by their formulation, curing process, surface preparation, and environmental conditions such as temperature and humidity [37]. The long-term durability of adhesives may degrade due to exposure to fire or extreme environmental conditions, raising concerns about their performance in specific structural applications. Adhesives exhibit a wide range of stiffness, with moduli of elasticity from 0.1 GPa to 15 GPa. Isocyanate-based adhesives, such as polyurethane (PUR), emulsion polyisocyanates (EPIs), and polymeric methylene diphenyl diisocyanate (pMDI), fall on the lower end of this range, offering flexibility. Phenolic and amino resin adhesives offer higher stiffness and superior heat resistance, making them suitable for structural load-bearing applications [38].

Adhesive connections are commonly used in the production of EWPs, such as CLT, LVL, and glulam. Structural glues facilitate full composite action by efficiently transferring loads between bonded elements without disrupting the timber’s fibres. Adhesives are employed in hybrid joints in combination with mechanical fasteners to enhance the ultimate bearing capacity, stiffness, and overall mechanical properties [39]. Mechanical fasteners alone typically offer high toughness but limited stiffness. The integration of adhesives addresses this limitation, resulting in joints that are stiffer while retaining their energy absorption capacity [40]. Recent studies have also examined the impact of imperfections in glued-in-rod connections, highlighting their influence on load-bearing capacity and long-term durability [41].

Adhesive bonding is also increasingly being adopted in timber–concrete composite systems, particularly in prefabricated construction. However, uneven surfaces in prefabricated concrete elements pose bonding challenges, often resulting in unbonded or discontinuous contact areas. These issues can be mitigated through the application of filler compounds and external pressure to ensure full surface contact. Timber–concrete joints typically exhibit nonlinear shear force–slip behaviour and tend to deform progressively under sustained loads. Notably, current Eurocode provisions often underestimate the stiffness and strength of such adhesive-based joints [42].

2.3. Interlocking Connections

Interlocking connections are joints in timber buildings that do not use metal or adhesives. The concept of interlocking connections originated primarily from traditional Japanese, Chinese, and European carpentry. With advancements in the timber industry, modern research explores innovative applications of these techniques beyond their traditional use. This development supports the shift towards prefabrication and the integration of digital fabrication technologies in timber construction.

In the literature, the performance and structural aspects of mechanical and adhesive joints are widely discussed, whereas interlocking connections are more often examined in terms of their visual appearance, efficient design, fabrication, and assembly.

Mortise and tenon connections involve a cavity (mortise) and a protruding tongue (tenon). These interlocking connections are adaptable to various angles and shapes and are widely employed in timber frames and furniture. Xu et al. (2024) developed a digital library of mortise–tenon joints, facilitating the design of adaptable timber housing [43]. Simple mortise and tenon joints can take square, rectangular, round, or tapered forms. Such variations as the gooseneck, dovetail, or partial dovetail enhance interlocking, which is crucial for addressing structural needs such as transferring forces and resisting rotation. Fang and Mueller (2023) investigated the application of “Nuki” mortise-and-tenon joinery in modern mass timber construction, demonstrating potential carbon savings and structural efficacy [44]. Lap joints provide a simple and effective connection by overlapping two pieces, commonly utilised in frame construction. Scarf and splice joints, on the other hand, facilitate the extension of lengths in timber through tapered or interconnected pieces, proving invaluable in applications such as boatbuilding. Notched joints, characterized by grooves interlocking two pieces, are prominent in log cabin construction, offering stability and resistance to movement [45].

Kanasaki and Tanaka (2013) evaluated the possibility of digital fabrication of timber joints using Tsugite and Shiguchi [46]. Tsugite is a traditional Japanese technique used to extend a member that is lacking in length, whereas Shiguchi is used to connect members at an angle. There are around 200 different types of Tsugite and Shiguchi formats available that are appropriate for a particular function [46]. Figure 4 shows a few of these jointing techniques.

Rebstock et al. (2015) introduced a novel concept of the “maker joint” (Figure 5) for EWPs [47], which consists of simple and thick gooseneck joints (Figure 6). Gooseneck joints exhibit a higher compressive strength than tensile strength and brittle failure behaviour under tension, which poses challenges in structural design.

Dovetail connections are among the oldest timber connections and have recently gained popularity as a sustainable solution to produce EWPs. There are four types of dovetail connections: double notch, half-notch, lock joint, and full dovetail/fishtail joints. A double notch offers a comparatively better performance than a half-notch connection. The lock-type connection is generally used in beams with larger dimensions [49]. Ilgın and Karjalainen (2021) proposed using dovetail wood boards as an alternative to adhesives for manufacturing multilayered wood panels used in floor slabs and shear walls [49].

Finger joints are a key interlocking technique used to manufacture long structural elements of EWPs, although they require the addition of an adhesive. The length of finger joints is the key parameter that defines the capacity of the joint. Fingers with relatively flat slopes and sharp tips can achieve strength even with shorter finger lengths. The risk of failure due to splitting is high. According to the experimental results, the presence of finger joints reduces the mechanical properties. The moduli of elasticity and tensile strength dropped by 11–19% and 27.5%, respectively [50].

3. Methodology

3.1. Data Collection and Search Strategy

This systematic review aimed to identify and analyse research on connections in EWP buildings with a focus on prefabrication. The literature search was conducted using the Web of Science Core Collection database to ensure high-quality and peer-reviewed sources as summarised in

Table 1. Search terms and number of records in the literature.

Field of Search	Search Term	Records
Topic	(“Engineered wood” OR “mass timber” OR “Timber”) AND (“connection” OR “joints”) AND (“prefabrication” OR “offsite”)	55
Title, abstract, author keywords	(“metal plate” OR “dowel type” OR “interlocking” OR “adhesive” OR “Fasteners”) AND (“Engineered wood” OR “mass timber” OR “Cross-laminated Timber” OR “Glulam”)	575

. A comprehensive keyword-based search strategy was employed to capture recent studies published from 2005 onwards that are relevant to EWP connections in prefabricated structures. The initial search yielded a total of 630 publications.

3.2. Screening Process and Analysis

The extracted records were merged into a single dataset, and duplicates were removed. A rigorous screening process was implemented to ensure the relevance and quality of the selected studies. After the screening process, 525 papers were selected for bibliometric analysis, while 125 publications underwent qualitative trend analysis.

• Duplicate removal: studies appearing in both queries were identified and removed.
• Title and abstract screening: each paper was assessed for its relevance to EWP connections in prefabricated buildings.
• Exclusion criteria: review articles, editorials, and conference abstracts without full-text access, non-English articles, and studies unrelated to the review topic.
• Bibliometric analysis: carried out based on 525 publications using the VOSviewer version 1.6.19 software.
• Abstract, results, and conclusion review for trend analysis: a subset of 125 full-text papers were selected for in-depth trend analysis based on their contribution to the field.

4. Results

4.1. Bibliometric Analysis

A total of 525 publications from 2005 to 2025 were reviewed for bibliometric analysis. Geographically, China, Canada, and the USA have shown significant engagement in this study area (

Table 2. Top ten countries with the highest number of publications in the area of study.

Country	Number of Publications
China	96
Canada	76
USA	62
Germany	43
Italy	43
Sweden	35
Australia	31
France	25
England	24
Switzerland	24

).

The steady rise in the number of publications, particularly the sharp increase from 2018 onward, indicates that research interest in connections for timber structures has grown exponentially, reflecting its increasing importance in modern construction and structural engineering (Figure 7).

According to the co-occurrence analysis, research trends link key terms such as “performance,” “strength,” “behaviour,” and “prefabrication,” highlighting critical areas in EWP and prefabrication research (Figure 8). The network visualisation map reveals four distinct clusters, with “performance” acting as the central node, connecting multiple clusters and emphasising its significance in structural evaluations. “Prefabrication” appears in the blue cluster, linking structural strength and component efficiency, reinforcing its role in EWP building systems. “Timber” and “connections” exhibit strong interlinkages, indicating the critical importance of connection systems in timber structures. The presence of terms such as “cross-laminated timber (CLT)”, “mechanical properties,” and “concrete” suggests ongoing research into hybrid construction methods and material behaviour, while “bonding” and “plywood” in another cluster highlight advancements in EWP performance. This analysis provides a structured insight into current research directions, emphasising the role of connections, material properties, and performance in optimising prefabricated timber structures.

4.2. Recent Trends in Literature

4.2.1. Prefabrication Adaptability

Prefabrication adaptability in buildings constructed with EWPs has gained significant attention in recent years. Key focus areas include the ability to assemble and disassemble structures and the suitability of interlocking connections in the prefabrication industry. As prefabricated construction evolves, the structural design of connection systems must continue to align with the fundamental principles of conventional structural engineering. This includes satisfying strength, serviceability, and stability criteria to ensure performance integrity throughout a building’s lifecycle. Designers are responsible for ensuring connection systems are not only structurally sound, but also easily accessible post-installation and facilitate rapid on-site assembly [51].

Interlocking connections, including finger joints, are widely used in the prefabrication of EWPs. Digitally fabricated dovetail joints have emerged as a reliable method for achieving interlocking connections in prefabricated timber structures [52] Larsson et al. (2020) and Rebstock et al. (2015) suggest that Tsugite connection systems are more suitable for the digital fabrication of wooden frame structures [47,53].

The advancements in reversible timber connection systems have been pivotal in enhancing the adaptability of EWP buildings. These systems are designed for ease of assembly, disassembly, and reuse—aligning with the principles of the circular economy and promoting sustainable construction practices [54].

4.2.2. Sustainability and Circular Economy

As sustainability becomes a key priority in construction, researchers are developing timber connection systems that support deconstruction, material reuse, and waste reduction. A comprehensive review by Ottenhaus et al. (2023) outlined design principles that facilitate adaptability through Design for Disassembly (DfD) and reuse. Recent studies have emphasised the role of reversible connections in modular timber buildings to align with circular economy principles [55]. Yan (2024) investigated novel reversible timber connections in Prefabricated Laminated Timber Frame (P-LTF) systems, demonstrating their effectiveness in facilitating adaptability and material recovery without compromising structural performance [56]. These findings highlight the importance of mechanical fastening techniques that enable full disassembly and reuse, thereby reducing construction waste and promoting a closed-loop material cycle.

Conventional adhesives, which are typically derived from petroleum-based materials, present environmental concerns, including formaldehyde emissions and low biodegradability [57]. This has prompted growing interest in greener alternatives. Recent advancements in bio-based adhesives formulated from lignin, starch, and proteins have shown promising results, achieving bond strengths comparable to synthetic resins while drastically reducing Volatile Organic Compound (VOC) emissions. Several bio-adhesives have already been incorporated into wood-based panels, resulting in ultra-low formaldehyde emissions and enhanced indoor air quality [58]. In parallel, research has explored the integration of natural fibre-reinforced composites into wood systems, offering biodegradable and renewable solutions with structural potential. These hybrid composites can contribute to sustainable construction by reducing dependence on petroleum-based components while maintaining high mechanical performance [59].

4.2.3. Hygrothermal Issues

Studies highlight the impact of moisture fluctuations and temperature variations on EWP connections. Timber and wood-based products are prone to deformation, shrinkage, swelling, and decay under changing environmental conditions, affecting connection performance. Proper detailing is essential to mitigate internal stresses, loosening of fasteners, and moisture-related deterioration.

Moisture content significantly influences connection performance and durability. Research focusing on the axial withdrawal capacity of self-tapping screws in cross-laminated timber revealed that increased moisture levels and varying displacement rates can markedly influence the withdrawal capacity, highlighting the need for careful consideration of environmental conditions [60]. A study observed that an increase in humidity and temperature led to a decrease in joint stiffness by 25% and strength by up to 40% [61]. Low-permeability materials have a higher risk of moisture problems and have a higher influence on material properties than that from environmental conditions. Corrosion levels of metal fasteners increase with repeated wetting and drying cycles, affecting the withdrawal strength [58]. Incorporating adhesives together with fasteners can improve the sealing of the connections against moisture ingress and corrosion [42].

4.2.4. Extreme Conditions

The performance of timber connections under seismic, high wind, and extreme temperature conditions has been explored in research focusing on the need for advanced joint designs to improve the resilience of buildings constructed with EWPs. Most studies have emphasised seismic performance, which is critical due to the unique challenges posed by dynamic loading.

In seismic design, traditional systems such as hold-downs and angle brackets have been widely used for energy dissipation. However, these systems often experience significant post-earthquake damage to structural components, which may affect the overall performance and lead to costly repairs or replacements [11]. In recent studies, novel connections such as the Resilient Slip Friction Joint (RSFJ) and Pinching-Free Connector (PFC) have been introduced to enhance ductility and better accommodate combined loading scenarios [62]. Experimental tests and numerical modelling were conducted to investigate the coupling effect of simultaneous shear and axial loading on connections, emphasising the need for its consideration in design models.

In high wind- or hurricane-prone regions, mechanically fastened panelised timber assemblies are being developed to withstand extreme lateral forces. Parametric FEM of racking behaviour in modular shear wall connections has confirmed that reinforced hybrid systems improve lateral stability [63].

Under fire exposure, timber connections experience changes in thermal conductivity, density, and charring rates, affecting structural integrity, which has been experimentally proven in research. Connection deformation and reduced yield strength at high temperatures can lead to failure, emphasising the need for fire-resistant connection designs. To improve fire performance, research has focused on self-extinguishing adhesives, char-resistant coatings, and metal-reinforced joints. Flexible polyurethane adhesives demonstrated reliable strength and ductility under elevated temperatures, making them suitable for shear-dominant and thermally demanding applications [64]. Fire performance of various connection types, such as bolted or nailed wood-to-wood and steel-to-timber joints, was reviewed by Maraveas et al. (2015) [65]. They provided insights into how different connections behave under fire exposure and discussed factors affecting their structural integrity.

5. Discussion

The selection of connection systems in buildings constructed with EWPs is a critical factor influencing structural integrity, long-term durability, construction efficiency, and sustainability. The key considerations in connection design within the timber prefabrication industry include:

1. Structural integrity, durability, and performance:

• Proper design ensures long-term structural reliability by preventing weak points that could lead to premature failure under applied loads.
• Consideration of effective stress distribution and optimised load path design is critical. Precise timber section sizing prevents failure under structural loads.
• Connection designs must comply with regional standards and building codes.
• Seismic and wind load performance is essential for buildings in high-risk regions. Connections must be ductile, capable of dissipating energy, and have optimised section geometry.
• Fire resistance of connections ensures stability under fire exposure through fire-resistant adhesives, coatings for fasteners, and embedded connection designs to minimise weakening.
• Moisture-induced swelling, shrinkage, and decay can be mitigated through tight-fitting dry connections, interlocking systems, or hybrid solutions.

2. Construction efficiency:

• Connection design should prioritise fast, simple, and precise connection systems to optimise on-site assembly.
• Connection types must align with timber geometry to ensure load transfer without excessive cutting, weakening, or material wastage.
• The design should enable easy, damage-free assembly and disassembly using reversible fasteners, interlocking joints, and prefabricated slots.
• Efficient connections facilitate on-site installation and maintenance with easy accessibility and adjustability.
• Errors can be reduced and on-site modifications minimised through precision manufacturing and digital fabrication, ensuring tight tolerances.

3. Sustainability and circular economy:

• Facilitate deconstruction and repurposing of timber elements through reversible connection systems.
• Bio-based adhesives and materials can be used to reduce environmental impact and promote material circularity.

In prefabricated buildings constructed with EWPs, one of the key challenges lies in optimising connection performance while ensuring compatibility with factory-produced components. Despite growing interest in innovative joint systems, the absence of comprehensive design standards for adhesive and interlocking connections continues to restrict their widespread use in practice. This limitation is compounded by the lack of standardised methods for assessing durability under variable humidity and temperature conditions, as well as under extreme loads such as earthquakes, strong winds, and fire exposure [66].

Recent developments in reversible connection systems and digital fabrication techniques have shown a potential to improve adaptability, disassembly, and alignment with circular economy principles. However, their adoption remains limited due to the extensive testing and validation required to meet safety and performance expectations.

In parallel, mass timber buildings have increasingly incorporated hybrid and damage-avoidance connection systems that prioritise structural resilience. The Clearwater Quay Apartments in Wellington employed post-tensioned Pres-Lam LVL walls with replaceable steel fuses, enabling controlled rocking and efficient energy dissipation during seismic events. Similarly, the NMIT Arts and Media Building used a hybrid Pres-Lam frame system with unbonded tendons and mild steel dissipaters to achieve both energy dissipation and recentring capacity [67]. These examples highlight the potential of well-designed connection systems to minimise structural damage and support rapid post-event recovery.

6. Conclusions

This study systematically reviewed connection methods in EWP buildings, emphasising their role in prefabrication and structural efficiency. While mechanical fasteners remain widely used due to their established performance, adhesive and interlocking connections offer opportunities for improved aesthetics, sustainability, and efficiency. Hybrid systems that integrate mechanical and adhesive components offer a promising balance of strength, resilience, and sustainability across diverse building applications. However, challenges such as durability, fire resistance, and standardisation persist, limiting the broader adoption of non-mechanical connections.

To advance the use of novel connections in prefabricated timber construction, future research should prioritise the standardisation of testing protocols and the development of robust modelling techniques. Additionally, there is a pressing need to refine design codes for emerging connection types and improve fire-resistant adhesives to ensure structural reliability. A key gap in current research is the absence of standardised long-term durability assessments, particularly under variable environmental conditions such as humidity, temperature fluctuations, and biological degradation. Addressing these issues is essential for evaluating connection performance over a building’s lifespan. Furthermore, innovations in digital fabrication and precision manufacturing warrant further exploration, particularly for their potential to enhance connection accuracy, reduce construction time, and minimise material waste. These advancements are critical to supporting the continued evolution of EWP construction as a sustainable and efficient solution for modern prefabrication.