Low-cost (Shoestring) digital solution areas for enabling digitalisation in construction SMEs

The adoption of digital solutions accelerated in the construction industry to increase the efficiency of manufacturing and construction processes. However, most construction SMEs face barriers to the digital transformation of their processes due to budget constraints and the complexity of the existing commercial digital solutions. In this study, we developed 58 digital solution areas for construction SMEs by adapting the Digital Shoestring Approach. These were generated through eight interactive digital requirement assessment workshops with 70 representative construction SMEs in the United Kingdom. The top fifteen priority digital solutions were identified based on the different operational requirements of Tier 1 (on-site construction SMEs) and Tier 2 (suppliers and off-site construction SMEs) SMEs in the construction supply chain. The findings showed that digital solution areas could provide cost-effective and evidence-driven digitalisation pathways for construction SMEs by systematically identifying their digital needs and priorities to meet Construction 4.0.


Introduction
The construction industry, with an economic output of about £ 110 billion per annum, is one of the pillars of the UK domestic industry, contributing to 9 % of the country's GDP in 2016 (Department for Business Energy and Industrial Strategy, 2019).The UK construction industry comprises over 300,000 businesses, of which 96 % are Small and Medium-sized Enterprises (SMEs) (Office for National Statistics (ONS), 2020b).57 % of the value of the UK construction work completed in 2020, which is more than £ 85 thousand million, was generated by SMEs (Office for National Statistics (ONS), 2020a).In this study, we used the term SME per the standard's definition (Department for International Trade, 2021), which refers to businesses with employee numbers < 250 and annual turnovers ≤ €50 million.Despite their huge contribution to the economy, construction SMEs lag in adopting digital solutions due to their financial and human resource constraints (HM Goverment, 2013) resulting in missed deadlines, delayed critical milestones, exceeded project budgets, lost money and reputational damage (Institution of Civil Engineers & Bluebeam, 2019).
The lifecycle of a construction project typically follows the RIBA Plan of Work (2020) which spans seven stages from strategic definition to handover and use (see Fig. 1).Each stage defines core tasks which can benefit from digitalisation to achieve the expected outcomes and information exchanges (as presented in Section 3.3).The focus of this study is the digitalisation of the construction SMEs which delivers Stage 5 of the RIBA Plan of Work (2020) through (i) the manufacturing of raw materials (cement, steel, etc.), building products (elevators, doors, windows, etc.) and systems (heating, ventilation, air conditioning systems, etc.), (ii) the prefabrication of building elements (truss, beam, footers, columns, etc.) and (iii) the construction of buildings and their elements.This construction supply chain is divided into Tiers as presented in Fig. 1; Tier 1 comprises on-site construction SMEs located at the centre with links to Tier 2, which includes construction suppliers and off-site construction SMEs (Department for Business Innovation and Skills, 2013).While Tier 1 is responsible for constructing buildings and building elements at a construction site, Tier 2 is mainly manufacturing companies producing building raw materials, products, systems, and elements in factories.(Berlak et al., 2021; Department for Business Innovation and Skills, 2013).Owing to the variations in their operational environments in Tiers 1 and 2, the digitalisation requirements of on-site construction SMEs are different from that of the suppliers and off-site construction SMEs, necessitating their requirements to be separated.To this end, this study creates a taxonomy of construction SMEs by clustering them into two: (i) on-site construction SMEs (Tier 1 suppliers) and (ii) suppliers and off-site construction SMEs (Tier 2 suppliers); by adopting the taxonomy advocated in the Department for Business Innovation and Skills (2013).
The digitalisation of construction SMEs is quite significant not only for improving the efficiency in their day-to-day operations (mitigating mistakes and reworks, reducing delays in critical milestones, and exceeding project budgets) but also for enhancing collaboration and integrated information sharing across the construction supply chain.Identifying and prioritising the digitalisation needs of individual construction SMEs while considering the diversity in their operational practices are key departure points for their agile digitalisation and further integration across the supply chain, both horizontally and vertically (Muñoz-La Rivera et al., 2021).The existing academic literature on the digitalisation of the construction industry usually focuses on highlighting the benefits and challenges of adopting digital technologies, particularly for Construction 4.0 and BIM (explained in Section 2); benchmarking the benefits, costs and risks of investments in digital technologies for construction SMEs (Love et al., 2004); and identifying factors and barriers to digitalisation (McNamara and Sepasgozar, 2021;Amaral and Peças, 2021).There is a lack of research studies on agile and low-cost digitalisation that breaks down the barriers to digitalisation of construction SMEs, which gives rise to the following gaps: • a structured approach for helping construction SMEs to understand their business problems (Love and Matthews, 2019) that will initiate and accelerate digitalisation on limited budgets and human resources (Neely and Schooling, 2019) (Dallasega et al., 2018) • identifying digitalisation requirements of construction SMEs while considering the diversity in their business operations (European Commission, 2019) and the fragmented structure of the construction supply chain (see Fig. 1).
This study addresses the first gap by developing a catalogue for digital solution areas for construction through action research, a list of 58 digital construction solution areas, which helps construction SMEs identify their business areas to be digitalised first and determine the priority digital solutions that will quickly transform these business operations into digitally enabled processes (Merschbrock and Munkvold, 2015a, 2015b, 2015c).We addressed the second gap by carrying out interactive digital requirements assessment workshops with 70 construction SMEs and identifying the top fifteen priority digital solution areas while considering the diversity of their business operations due to their different working environments across the fragmented construction supply chain.
The rest of the paper is divided into five sections: Section 2 provides an overview of digitalisation in the construction industry while Section 3 presents the methodology to develop the Catalogue of Digital Construction Solution Areas, including the solution areas' definitions.The top fifteen priority digital solutions selected by the construction SMEs are presented in Section 4. Conclusions are drawn and, limitations and future research directions are highlighted in Section 5.

Digitalisation in the construction industry
Industry 4.0 has been transforming manufacturing industries such as automotive (Craveiro et al., 2019), agriculture (Frank et al., 2019), and chemical (Li et al., 2022) by connecting the embedded production systems, and processes through cyber-physical systems, thereby driving a shift towards smart manufacturing and factories (Jeon et al., 2017).The construction industry, the most traditional sector that digitalisation has impacted the least, is being influenced by Industry 4.0; referred to as Construction 4.0 (Berger, 2016).However, Construction 4.0 differs from Industry 4.0 by focusing on the industrialisation of constructing unique and customised building products rather than the serial production of the same product (Klinc and Turk, 2019).In contrast to manufacturing systems where multiple products pass through a factory before being delivered to many customers, the construction factory is set up in an on-site environment to produce a single product for a particular project (Young et al., 2007).This unique construction production and the on-site environment impact the development and integration of digital solutions for construction SMEs (European Commission, 2019).
Construction 4.0 aims to increase productivity, quality and safety; and reduce cost, waste and inefficiencies (Sawhney et al., 2020).It is classified into two technology pillars namely, the digitalisation of the construction supply chain and the industrialisation of construction processes (Oesterreich and Teuteberg, 2016).The digitalisation of the construction supply chain aims to increase productivity through the efficient collaboration and horizontal, vertical and longitudinal integration of construction organisations from different domains such as suppliers (Mechanical, Electrical and Plumbing (MEP) components and raw materials suppliers, etc.), off-site (pre-fabricators, modular builders, etc.) and on-site (main contractors).On the other hand, the industrialisation of construction processes focuses on the mass production of customised building elements (Forcael et al., 2020).These technology pillars are supported by smart construction sites, digitalisation and virtualisation technologies, and simulation and modelling (Oesterreich and Teuteberg, 2016).The smart construction sites include cyber-physical systems and automation using RFIDs, sensors and drones while enabling bi-directional coordination between digital twins and physical facilities (Y.Jiang et al., 2022;Weyer et al., 2015).Smart construction site-related digital solutions can be implemented indifferently based on the monitoring requirements and complexity of the sensors for mapping (e.g., laser scanners, RGB, depth cameras, ground penetrating radar), positioning and communication (e.g., tracking devices, global navigation satellite systems, etc.), and sensor platforms (e. g., stationary, handheld, wearable, etc.) (Rao et al., 2022).Modern methods of construction also benefit from modularisation, prefabrication and 3D printing (Cassino et al., 2011); process monitoring solutions implemented based on different types of methodologies such as scene understanding, positioning, and tracking for monitoring workers and hazardous situations (Rao et al., 2022), machine diagnostic, work progress monitoring, and project site security (Project Management Institute, 2016); and robotics for on-site and off-site construction (Sherratt et al., 2020).Digitalisation and virtualisation consist of cloud and mobile computing, big data and data analytics (Oesterreich and Teuteberg, 2016) and blockchain (Li et al., 2019).The simulation and modelling are supported by Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR) technologies connected with BIM for manufacturing and construction support (Um et al., 2023); and quality inspection and monitoring (Sacks et al., 2020).
BIM is considered to be the main enabling technology for Construction 4.0 by generating an environment which integrates various digital solutions, platforms, servers, and libraries (Sacks et al., 2020).BIM is the process of generating object-oriented 3D parametric models and storing, sharing, and integrating these models for constructing and operating facilities during the life cycle (NBIMS, 2015); thereby improving collaboration and information sharing across the construction supply chain network (Eastman et al., 2008) and mitigating rework and unnecessary costs (UKBIMA, 2021).Due to its numerous benefits, several countries such as Finland, Sweden, Denmark, the United Kingdom, Singapore and the United Arab Emirates mandate the implementation of BIM (Charef et al., 2019;R. Jiang et al., 2022;Mehran, 2016).On the contrary, countries such as the United States of America (USA) prefer industry-driven approaches to BIM adoption (R. Jiang et al., 2022).International BIM standards such as BS EN ISO 19650 (BSI Standards Publication, 2018a, 2018b, 2020a, 2020b) also aid its effective implementation and have been supported by academic research on the integration of BIM into operations at different stages of the construction project lifecycle.For instance, BIM has enabled visualisation, clash detection, quantity take-off, cost estimation (NBIMS, 2017) and automated code compliance checking in design (Amor and Dimyadi, 2021); progress monitoring and scheduling (Hong et al., 2022), and quality control in construction (Leygonie et al., 2022); and maintenance decision making for facility management (Um et al., 2023).BIM is also used as a medium for communicating information within a construction team, as demonstrated in a case study of an off-site precast concrete fabrication facility (Demian and Walters, 2014;Wang et al., 2020).Nevertheless, on-site construction companies comparatively find BIM to be more relevant to their operations than off-site companies, especially subcontractors who are specialised in a particular domain such as MEP suppliers (UKBIMA, 2021).For instance, validating the design using the BIM model by on-site contractors and designers reduces construction waste (e.g.reducing 4.3-15.2% of construction waste (Won et al., 2016)).Moreover, BIM-based prefabrication is expected to be increasingly used by main building contractors, green building practitioners, and MEP subcontractors to reduce site labour, waste and the quantity of materials used, thereby adopting green building practices (Jang et al., 2022).
Adopting Construction 4.0 and BIM is usually dependent on each other since BIM provides a central hub environment for integrating data collected through various technologies such as sensors, RFID, GPS, lidar, GIS, and AR/VR (Manzoor et al., 2021).Besides the proven benefits of Construction 4.0, it still has high implementation costs, unclear value propositions, lack of standards, cybersecurity concerns, and inefficiencies (Sawhney et al., 2020).Complexities arising from on-site implementation such as high-cost of sensors and their deployments (e. g. lidar for construction site monitoring), inefficiencies (e.g.manually creating as-is BIM based on lidar scan data) and lack of standards (e.g.lack of indoor evaluation for autonomous navigation and mapping of a construction site) remain barriers to digitalisation for on-site construction companies (Rao et al., 2022).The impact of these challenges is exacerbated for SMEs, who are critical for driving digitalisation in the construction industry (Lekan et al., 2021).While efforts are undergoing to encourage BIM adoption with SMEs (Awwad et al., 2022;Pham et al., 2020), replacing existing processes with BIM-integrated project deliveries requires considerable financial and human resources such as the cost of technical infrastructure, a BIM-savvy workforce, and cultural/behavioural change in construction organisations (Yilmaz et al., 2019).In the UK, large (81 %) and medium (76 %) enterprises adopt BIM quickly through more significant financial investment opportunities and human resources in comparison to micro (36 %) and small (57 %) organisations (UKBIMA, 2021).The NBS (2021) reported that 55 % of the UK's construction SMEs are less likely to have adopted, and 10 % will never use BIM.In the USA, 52 % of large enterprises and 20 % of construction SMEs use BIM for visualisations, delivering design intent to construction, enhancing project collaboration and producing 3D deliverables (Dodge Data and Analytics, 2021).BIM adoption rates in the public sector have also been slow due to the lack of short-term benefits with a long payback period, lack of client demand, interoperability issues between technologies, and unclear information requirements (European Innovation Council and SMEs Executive Agency, 2021).Additionally, most BIM tools and platforms do not support emerging out-of-the-box digital solutions which generate interoperability issues across the construction supply chain (Sacks et al., 2020).
A systematic approach for developing and adopting low-cost and customisable digital solutions is needed by construction SMEs to overcome the aforementioned barriers of enabling technologies such as inflexibility, lack of supporting customisation, high implementation costs, legacy issues, etc.Such an approach will facilitate the identification of their digital needs and prioritise and deploy low-cost digital solutions based on their daily operations rather than solely acquiring highcost and less flexible off-the-shelf digital solutions.,To this end, this research develops a catalogue of digital solution areas for construction by adopting the Digital Shoestring Approach (DSA) which was successfully implemented for the low-cost digitalisation of manufacturing SMEs.DSA is a logical step-by-step approach starting with identifying the digital requirements of SMEs and focusing on the design and development of low-cost digital solutions (Mcfarlane et al., 2019).It uses commercial off-the-shelf hardware components (e.g.microcontrollers and microcomputers such as Arduino Uno and Raspberry Pi) and open-source software libraries (e.g.visualisation and communication libraries such as Grafana and ZeroMQ) (Hawkridge et al., 2021;Martínez-Arellano et al., 2021).The critical part of this approach is a modular and reusable design method which embeds low-cost technologies into standard building blocks developed to counter solution-driven approaches that are often used within Industry 4.0.The catalogue of digital solution areas for construction was developed through interactive requirement workshops with construction SMEs.The empirical results from these workshops show that the Catalogue helps construction SMEs identify their digitalisation priorities and facilitate their low-cost digitalisation which is the initial step for increasing their digital awareness.

Development of a catalogue of digital solution areas for construction
This study follows action research, which seeks to solve problems by producing knowledge both for practice and theory through a cyclical process (Dresch et al., 2015).The three steps of action research given by Azhar et al. (2010), which are 1) problem diagnosis, 2) planning and taking action, and 3) evaluation and learning, which are represented in Fig. 2 with different colours, were adopted to develop a Catalogue of Digital Construction Solution Areas.The use of two or more research methods to investigate the same thing, approaches to data collection and sources of data, called triangulation, is recognised to improve the rigour of qualitative research in construction (Fellows and Liu, 2015).Thus, we used triangulation by conducting interactive digital requirements assessment workshops with the construction SMEs, the main research activity, as well as literature search and expert reviews which were intermediatory steps to augment the terminology to suit the digital solution areas and to identify the suitable digital solution areas for construction (Fig. 2).
The Catalogue of Digital Manufacturing Solution Areas is composed of 53 digital solution areas for manufacturing which are systems facilitating an activity without referring to a concrete technological implementation (Schönfuß et al., 2021).These 53 digital solution areas were taken as a baseline and adapted to the construction industry iteratively through the interactive digital requirements assessment workshops.We engaged with 70 construction SMEs to identify digital solutions that would be useful for their operations in the short term.The suggested digital solutions were then used to add and refine the Catalogue for the construction industry iteratively.This cyclic feedback loop continues until the construction SME participants introduce no new digital solutions during the workshops.We terminated adding and refining the Catalogue when no new digital solutions for construction were introduced.Thereby, the final version of the Catalogue of Digital Construction Solution Areas, presented in Table 5, consists of 58 digital construction solution areas.While two solution areas are specific to suppliers and off-site construction SMEs (Tier 2 suppliers), five solution areas only apply to on-site construction SMEs (Tier 1 suppliers).The interactive digital requirements assessment workshops and the literature search and expert reviews are explained in Sections 3.1 and 3.2, respectively.

Digital requirements assessment workshops with construction SMEs
Two separate series of eight interactive digital requirements assessment workshops were conducted after creating a taxonomy of construction SMEs by clustering them into two: 1) suppliers and the off-site construction SMEs (Tier 2, 32 participants) and 2) on-site construction SMEs (Tier 1, 38 participants).Construction SMEs who participated in the workshops were representatives for identifying the digital needs of Tier 1 and Tier 2 suppliers in the construction supply chain who have different operational environments explained in detail in Section 1. Tier 1 suppliers consist of on-site contractors who are the main contractors performing on-site construction represented by 20 % of the participants in Fig. 3. Tier 2 suppliers are composed of suppliers (manufacturers of raw materials, building products, and systems represented by 16 % of the participants), sub-contractors (engineering and design contractors, workforce contractors, and consultants represented by 34 % of participants), service providers (digital service providers such as building inspection and facility management systems represented by 10 % of the participants) and off-site contractors (modular house builders represented by 7 % of the participants).While 13 % of the construction SMEs were not clustered under any of the groups (others that are facility management services), 20 % and 67 % of the construction SMEs are clustered under Tier 1 and Tier 2 suppliers in total, respectively (Fig. 3).The construction SME participants have varied experiences of involving in various types of projects including buildings and infrastructure.
As presented in Fig. 2, the interactive digital requirements assessment workshops yielded two outcomes: 1) suggested digital construction solutions by the participants and 2) the top priority digital solution areas for construction SMEs.The digital solutions suggested by the SMEs' participants were captured through the two open-ended questions about 'what digital solutions would be adopted in the short term' and 'what benefits those solutions brought to their businesses'.These questions were asked at the beginning of the workshops in order not to create any bias by allowing construction SMEs' representatives to see the existing digital solutions in the Catalogue.The participants' responses were captured in a list of suggested digital solutions which was used for adding and refining the digital construction solution areas in the Catalogue.Tier 2 and Tier 1 participants suggested 27 and 33 digital solutions (60 in total), respectively.Ten of the participants did not suggest any digital solution; hence, in total 60 digital solutions were assessed whether to add them to the Catalogue or not, based on the following four criteria: • Not clear: suggestions do not imply solutions and are too general and ambiguous such as off-site manufacturing and customer stakeholder engagement.• Not low-cost/shoestring: suggestions not considered standalone and low-cost (shoestring) solutions such as customer resource management system and BIM.• Already exists in the catalogue: suggestions already exist as shoestring solutions in the Catalogue.• New solutions to be added: suggestions that are considered new standalone and low-cost solutions to be added to the Catalogue.
The assessment results are summarised in Table 2.The solutions which were marked as new solutions were added to the Catalogue.
On-site construction SMEs' inputs were either related to the main construction operations that already existed in the Catalogue or too general, thereby, no new solutions were introduced (see Table 1).For example, linked costing and billing software that is introduced by on-site construction SMEs is one of the main construction operations related to cost control and corresponds to sales/progress payments tracking and support in the Catalogue.Another input introduced by on-site construction SMEs' representatives, document generator and management, was marked as Not Shoestring as it is too general to be added to the Catalogue.While a platform for communicating with staff was added to the Catalogue as tracking site queries, a tool for understanding how to help clients with third-party solution recommendations was added as contractor section and decision support.No modification has been made based on the 33 digital solution suggestions introduced by the on-site construction SMEs' participants.Hence, we concluded that the final version of the Digital Construction Solutions Catalogue consists of 58 digital construction solutions.While four of the 38 Tier 1 suppliers and five of the 32 Tier 2 suppliers suggested integrating BIM for designing, coordinating, costing, tendering, scheduling, facility and change management, a consensus was reached during the discussions that using BIM would not be classified as low-cost considering the significant technological and financial investments for acquiring and developing these digital  solutions aligning with the literature (Saka and Chan, 2020).Alternatively, low-cost digital solutions for fulfilling these activities were included in the catalogue which can be implemented by using various technologies.

Expert reviews and literature search
We aligned the titles and the definitions of 55 digital solution areas for Tier 1 suppliers that are composed of on-site construction SMEs through a literature search, an intermediary research activity.The literature search also resulted in adding three solutions, which are worker time management (time tracking) system in terms of human resource, pre-completion activities planning for handover and cost tracking of items outside the building contract (RIBA, 2020) to the Catalogue which 58 digital solution areas for construction as presented in Fig. 2. Semi-structured interviews were performed with three experts who were selected based on their backgrounds, sectors and countries in which they are working.The first expert is an academic who has been working on construction engineering and management for more than 20 years in Türkiye; the second expert is both an academic and a practitioner in the construction industry who has been working as head of real estate planning and asset management for more than 20 years in the US and the third expert is the head of digital construction specialised in the digital transformation of construction SME in the built environment in the UK.Expert reviews, as an intermediary step between the two series of workshops, confirmed if digital solution areas are relevant to Tier 1 (on-site construction SMEs), Tier 2 suppliers (suppliers and off-site construction SMEs), or both by marking them as Applicable (A) or Not Applicable (NA) to Tier 1 and Tier 2 suppliers.All three experts confirmed that digital solution areas (integration with logistics providers and automated generation of basic CNC) are only relevant to the Tier 2 suppliers (suppliers and off-site construction SMEs) (Table 2).Five solutions (tracking site queries, contractor selection and decision support added via workshops; and cost tracking of items outside the building contract, pre-completion activities planning for handover, and worker time management (time tracking) system in terms of human resource added through literature search) were relevant to the Tier 1 suppliers (on-site construction SMEs).

The catalogue of digital solution for construction
The Catalogue of Digital Solution for Construction, presented in Table 2, is a comprehensive set of digital solution areas that support the digital transformation of manufacturing and construction processes of constructions SMEs.The definitions of the digital solution areas for the construction industry (see Appendix) informed the development of the Catalogue presented in Table 2.The final version of the Catalogue of Digital Construction Solution Areas consists of 58 digital construction solutions which were included in two subsets: 1) suppliers and off-site construction SMEs (Tier 1 suppliers) and 2) on-site construction SMEs (Tier 2 suppliers).
Each digital construction solution area has a holistic definition that sets its scope for digitally supporting the manufacturing and construction processes (see Appendix).Digital construction solution areas are technology agnostic and can be implemented using different technologies based on user, and technical specifications of construction SMEs.58 digital construction solution areas were categorised into four services namely Data Capture and Visualisation (DC & V), Data Analysis (DA), Actuation (A), and Decision Support Systems (DSS) following the same approach suggested by Scho¨nfuß et. al. (2021).While DC & V includes digital solution areas (47 % of the Catalogue) that primarily facilitate data capture and visualisation for the core manufacturing and construction processes, solutions in the DA category (34 % of the Catalogue) use simple analysis methods for interpreting the data.Category A comprises solution areas (7 % of the Catalogue) that control and trigger the flow of events through flexible parts and material handling support systems such as on-site robots.Lastly, DSS solution areas (12 % of the Catalogue) provide insights about alternatives at a point of decisionmaking for managing a particular operation.
The 58 digital construction solution areas were mapped to the core tasks of the project strategies namely cost plan, health and safety, inclusive design, planning, plan for use and sustainability, as defined in the manufacturing and construction phase of the RIBA Plan of Work (Table 3).This mapping helps the construction industry's practitioners to locate themselves under one of the strategies of construction projects and select relevant digital solutions for their agile development and deployment.For example, managing work payments based on building contracts is one of the core tasks of the cost plan strategy which can be supported digitally by five digital construction solutions.The manufacturing and construction systems related to the construction phase plan under the health and safety strategy could be digitally transformed by the nine digital solutions; some examples are digitised work instructions and assembly procedures, automated bottleneck identification in construction operations, digital job cards, and process monitoring.

Digitalisation priorities of construction SMEs
We followed a similar approach to the DSA while conducting digital requirements assessment workshops and identified the top ten priority digital solutions of construction SME.First, we asked SMEs' representatives to reflect on their business goals regarding order winners, choosing one of Price, Quality, Unique Value, Delivery and Ethical Position and to identify business challenges based on Business Constraints, choosing one of People and Information, Plant and Equipment, Supply Chain, Demand, and Cash.While Oder Winner is the competitive factor that customers prefer SMEs, Business Constraint is the internal limitation that prevents the SMEs' growth (Schönfuß et al., 2021).The digital solution areas for construction was filtered based on the Order Winner and Business Constraint selections of the participants.A sub-list of digital construction solutions was shown to help them give three and five votes for the highest and medium priority digital solutions, respectively.To represent both types of priority selections in one unified raking, a normalised priority score for each digital solution was calculated based on the following formula (Schönfuß et al., 2021): The operational environments of on-site and off-site construction SMEs influence their digital solution needs.This is reflected in the results of the order winners and business constraints of the representative SMEs interviewed in this study (see Fig. 4).The top Order Winners of suppliers and off-site construction SMEs (Tier 2) was identified as Unique Value (i.e., of the product/service) with a value of 49 % and 33 % of them highlighted the Quality of their service is key.These agree with the growing demand and advantages of prefabrication for construction projects.In contrast, the majority of on-site construction SMEs (Tier 1) identified Quality (51 %) as the top order winner and believe that they  (#of priority selections made) i (#of priority selections allocated per participat) i can win orders by offering high-quality service/product.This translates to acquiring digital solutions for quality tracking, automated quality inspection and automated quality checking.On the other hand, the unique value, price and delivery of the services were found to be of secondary importance for the on-site construction SMEs as it often depends on external factors such as fluctuations in the price and availability of raw materials that are often beyond their control.The constraints due to supply chain, demand and finance appeared to be relatively similar for both the construction SME types; a reflection of the operational challenges that SMEs face in general.Considering their nature of construction operations, a handful of on-site construction SMEs highlighted the accessibility to plants and equipment as a constraint to their operation.We realised that zero votes were given for the Plant and Equipment, which was not the case for the manufacturing SMEs (Schönfuß et al., 2021).The votes given for the Plant and Equipment by on-site construction SMEs is negligible (5 %).We envisaged that this low level of votes given for Plant and Equipment depends on the work environment of the on-site construction organisations, which perform their construction processes on-site rather than manufacture products in factory spaces.
Fig. 5 summarises the top fifteen priority digital solution areas selected by both suppliers and off-site construction SMEs (Tier 2) and on-site construction SMEs (Tier 1).The unified change management and issue reporting between design and production operation was selected as the top priority solution by suppliers and off-site construction SMEs (Tier 2).This solution could greatly impact improving the design quality by capturing the changes and eliminating them in the long term.One of the major challenge in the construction industry is tracking and managing change requests, which may create design and cost implications.Hence, it was not surprising to see the unified change management and issue reporting between design and production operations selected as the top priority digital solution.This group's second priority digital solution is digitised work instructions and assembly procedures.We defined the scope of this solution as providing the operator with high-quality instruction for completing specific operations together with supporting documents.One of the SME representatives introduced its time-saving benefit by saying quick roll out of drawings and instruction.This attendee also defined the expected features of the potential tool of this solution as clear digital images, drawings and instructions specific to workstations.The rest of the eight solutions presented in Fig. 5 were equally voted.Fig. 5 shows that votes given for the construction scheduling, process monitoring and unified change management and issue reporting between Fig. 4. Top order winners and business constraints of suppliers and off-site construction SMEs (Tier 2) and on-site construction SMEs (Tier 1).
G. Yilmaz et al. design and construction operations are equal; hence these three digital solutions were marked as the top three priority digital solutions by onsite construction SMEs (Tier 1).Construction scheduling is defined as creating a schedule/work plan for the construction of a building based on an approved design.One of the on-site construction SMEs who voted for the construction scheduling identified the expected features as creating weekly schedules by merging these schedules for a better highlevel view.Another on-site construction SME representative summarised the construction scheduling as seeing the construction schedule as simple as possible and visualising the progress of the construction against the schedule.This description covers more than one solution area which is the integration of three solutions which are construction scheduling, dashboard of construction progress (construction job tracking) and display of construction schedule/work plan.Process monitoring is defined as reporting the state of a process by measuring process key variables.We understood that this solution area is a common need by most on-site construction SMEs.For example, one of the on-site construction SMEs wanted to adopt this solutions area to track the progress and quality of the construction based on the site records and provide accurate invoices based on those progress records.The second priority digital solution voted by the on-site construction SMEs is digitised work instructions and assembly procedures was also ranked as the second priority solution area by the suppliers and off-site construction SMEs (Fig. 5).A modular on-site construction SME defined the expected features for the digitised work instructions and assembly procedures solution area as having a digital tool that helps the factory construction team and the end-user (asset owner) to track and maintain materials used in homes.The expected benefits of a potential digital tool of digitised work instructions and assembly procedures are monitoring the performance of the homes and knowing the materials used in the homes.The possible challenges to developing and implementing this solution were the cost of development and deployment and explaining its value to their customers.Digitised employee training received four votes from on-site construction SMEs as opposed to suppliers and off-site construction SMEs (three votes) since on-site construction operations are more diverse and complicated than the manufacturing processes of suppliers and off-site construction SMEs.The six digital solutions presented in Fig. 5 have similar priority scores, making them equally important in terms of onsite construction SMEs' business goals and challenges.
As presented in Fig. 5, Unified change management and issue reporting between design and operations is the top priority digital solution voted equally by both suppliers and off-site construction SMEs (Tier 2) and onsite construction SMEs (Tier 1) suppliers.Most off-site construction SMEs representatives (i.e.modular house builders) chose it as a priority digital solution compared to the suppliers' representatives (i.e. manufacturers of raw materials, building products, and systems) within Tier 2 suppliers.The manufacturing SMEs also ranked this digital solution as high which was the second top priority (Schönfuß et al., 2021).Digitised work instructions and assembly procedures ranked as the second priority digital solution which received equal votes from suppliers and off-site construction SMEs and on-site construction SMEs.A supplier representative (valve and actuator producer) preferred this solution to improve production efficiency by having a record of the work instruction used for assembly and receiving the right work instruction automatically.This solution ranked as the third priority digital solution by the manufacturing SMEs (Schönfuß et al., 2021) Process monitoring is the top third solution, rated mostly by suppliers and off-site construction SMEs (three votes in Fig. 5) rather than on-site construction SMEs (six votes in Fig. 5).Process monitoring was also ranked high as fifth in the top 15 priority digital solution areas for manufacturing (Schönfuß et al., 2021).Although these top three digital solutions for construction are identified as common solutions required by both groups of SMEs, their tool implementations can differ based on the different user and technical specifications.For example, an on-site construction SME's participant defined process monitoring as a simple tool for capturing real-time design information, including several main features such as allocating roles and tasks, including responsibilities matrix, tracking completed tasks, accessing up-to-date information from different locations, and seeing progress and placed orders in a tracker.Another on-site construction SME participant, who selected process monitoring, has tool specifications such as storing historical data based on different sites, accessing site-based historical data, and sending alerts to employees with instructions.
While 4D virtual project planning (3D rendering) was ranked fourth in the construction's chart, simulation of tools and processes for virtual planning, its equivalent in manufacturing, was selected as the twelfth priority digital solution in manufacturing (Schönfuß et al., 2021).This significant difference in ranking arises from the distinctions between operational environments in factories and construction sites.On-site construction SME representatives need this solution to improve productivity, save time and report site conditions quicker in projects by digitising workflow through 4D virtual project planning using laser scanning, processing, modelling and reporting.Construction scheduling (fifth rank) and display of construction schedule/work plan (sixth rank) received six and three votes from on-site construction SMEs, respectively.On the other hand, both two solutions received one vote from suppliers and off-site construction SMEs (Fig. 5).Job scheduling in the manufacturing catalogue, equivalent to construction scheduling, was ranked as the tenth priority solution by manufacturing SMEs (Schönfuß et al., 2021).Digitised employee training and job setup support ranked eighth and thirteenth in the construction chart while it was not listed within the top fifteen list of manufacturing.This difference arises due to the need for providing the operators with high-quality training and job setup support for specific on-site operations which might be accustomed to the unique construction projects.These solutions are also preferred to increase the health and safety of a construction site.Digital job cards were ranked tenth while receiving equal votes from both groups (three votes in Fig. 5), which could impact manufacturing and construction processes by tracking the jobs on a shopfloor and on-site through barcode scanners.Digital job cards were given the same importance by manufacturing SMEs selecting it as the eleventh priority digital solution (Schönfuß et al., 2021) while it was selected as the fourth priority digital solution by the suppliers and off-site construction SMEs.Internal lead time monitoring was ranked with similar importance in construction (ninth in Fig. 5) and manufacturing (eleventh in (Schönfuß et al., 2021)).
The top 15 priority digital solution areas for construction are different than that of manufacturing.Some of the common digital solution areas were only listed in the top 15 priority digital solutions of construction (Fig. 3).Automated generation of basic CNC code is only applicable to suppliers and off-site construction SMEs; hence, the on-site construction SMEs did not give any votes for it (zero in Fig. 5).Qualityrelated digital solutions (i.e.automated quality inspection and automated completeness checking ranked as seventh and ninth, respectively in Fig. 5) were not selected as top-priority solutions by the manufacturing SMEs.On the other hand, these quality-related digital solutions are quite impactful for the Tier 1 suppliers to improve efficiency in on-site operations by ensuring what's being built is within specifications, installed correctly, constructed as designed and on time for generation of snags/ defects/delayed or accelerated programmes.Project management system and asset product lifecycle management were only selected by the construction SMEs as top priority digital solutions for keeping the project on track, building and managing efficiently and safely, recording lessons learnt/improvements and training matrix for operatives on-site.The reverse is also true i.e. some of the common digital solution areas were only listed in the top 15 priority digital solutions of manufacturing (Schönfuß et al., 2021).Although some of the digital solution areas (i.e.real-time tracking of internal jobs (location, status), capacity monitoring of human and machine resources, customer and demand data gathering and analysis, automated optimisation of process parameters and predictive equipment maintenance) were ranked high (in top 8) in manufacturing due to their support for the flow of the operations within a factory, these solutions did not appear within the construction's top 15 priority digital solutions chart.

Conclusions
This study's contributions are twofold: 1) contribution to the literature and 2) practical contribution to the construction industry.We contributed to the literature by developing the digital solution areas for construction through action research which consists of 58 digital construction solutions areas by engaging with 70 construction SMEs.While two digital construction solutions apply to the suppliers and off-site construction SMEs (tier 2), five of the new digital solutions added to the Catalogue are specific to on-site construction SMEs (Tier 1) (see Table 2).Existing literature on digital construction mentions that most construction SMEs couldn't initiate digital transformation due to a lack of budget and digital awareness.The digital solution areas for construction presented within this paper could be used as a starting point for digital transformation of construction SMEs.Moreover, each digital construction solution area was mapped to the core tasks of the project strategies of the manufacturing and construction stage of the RIBA Plan of Work (RIBA, 2020), which will help construction SMEs to understand which digital construction solution could be integrated into which tasks.The digital construction solution areas were mapped to Construction 4.0 concepts to show how the Catalogue of Digital Construction Solution Areas contributes to Construction 4.0 concepts for ease of understanding with that of current digitalisation approaches of the construction industry (Table 4).The digital solutions deployed in Construction 4.0 usually require a significant change in SMEs' core processes owing to their integration with existing systems.On the other hand, low-cost  5,18,24,31,32,33,35,40,41,42,44,45,47,48,49,50,51,56 simulation and modelling augmented reality, virtual reality, mixed reality.
The practical contribution of this study is identifying the top fifteen priority digital solutions of suppliers and off-site construction SMEs (Tier 2), and on-site construction SMEs (Tier 1) (see Fig. 3).Unified change management and issue reporting between design and production and construction scheduling were selected as the top priority solutions by Tier 2 and Tier 1 construction SMEs, respectively.The top five priority digital solutions selected by both Tiers 1 and 2 are unified change management and issue reporting between design and operations, digitised work instructions and assembly procedures, process monitoring, project management systems and automated quality inspection.However, implementation of these common solutions could vary based on the diverse user and technical requirements of Tier 1 and Tier 2 construction SMEs.Some potential benefits and challenges of digital construction solutions after deployments defined by construction SMEs are presented in Table 5.
The digitalisation of construction SMEs is a topic of growing importance internationally.While the digital solution areas for construction SMEs presented in this study are developed based on our interactions with 70 construction SMEs in the UK, the results are relevant for construction SMEs across the world.Further research needs to be conducted to understand the factors that influence the adoption and implementation of digital solutions in construction SMEs in different countries.This includes understanding the barriers and enablers to digitalisation, the role of government policies and regulations, and the impact of cultural differences on technology adoption.Although the comprehensiveness of the digital solution areas for construction is validated by revising the catalogue based on the systematic evaluation of the digital solutions introduced in the workshops conducted with 70 construction SMEs, additional relevant solutions may exist.We mentioned that the catalogue is technology-agnostic; we expect that technological changes do not bring any revisions to the Catalogue.But on the other hand, as technology evolves, ways of conducting manufacturing and construction change rapidly and new digital solution areas should be added along with the latest construction methods, such as modern methods of construction.Secondly, the scope of the digital solution areas for construction is limited to the Manufacturing and Construction phase of the RIBA Plan of Work, which means that it focuses on Tier 1 (main contractors) and Tier 2 suppliers (material suppliers and fabricators) in the construction supply chain.Its scope could be extended to the other stages, such as Design and In Use of the RIBA plan of work.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 2 .
Fig. 2. Action research flow for developing the catalogue of digital construction solution.

Fig. 5 .
Fig. 5. Top fifteen priority solutions selected by suppliers and off-site construction SMEs, and on-site construction SMEs.

Table 1
Number of suggested digital construction solutions against defined criteria.
collection with data validation alerts, quality control on home retrofit measures, digital quality control and inspection process, workflow organiser, product tracking within fabrication and document handling, better customer relations database, data storage and client data portal, planning for full digitalisation of finance department, digital project management system New solutions 2 A platform for communicating with staff, a tool for understanding how to help clients with third-party solution recommendations 0 -Total 27 33

Table 2
Catalogue of low-cost (Shoestring) digital solutions for construction.

Table 3
Low-cost (Shoestring)digital construction solutions mapped to project strategies' core tasks of manufacturing and construction (RIBA, 2020).

Table 4
Mapping of the catalogue of digital construction solution areas to Construction 4.0 concepts.

Table 5
Potential benefits and challenges collected from representative construction SMEs.