1. The Workplace and Its Effect on Employee Engagement
The general aim of complementary building certification schemes available on the global market is to provide better office working environments for their users, with a positive impact on both the external environment (e.g., air quality outdoor) and indoor environmental conditions (e.g., lighting, temperature, noise, etc.), as well as health and well-being 
. Also, while evidence to date has shown that these certifications can help to achieve upgraded employee work performance (which is linked to engagement), they have been designed specifically for traditional corporate office environments that have been the dominant form of physical workplaces 
. For example, data from third-party survey providers has shown that such high performing workplaces, which prioritise experience and well-being, are linked to employee health, engagement and satisfaction; but this data is limited 
. Additionally, while many survey providers do have work-from-home modules, they are primarily designed for more traditional offices that may not fully correspond with the characteristics of home workplace environments 
Due to higher construction and fit-out costs for developers and business enterprises who want to meet the certifications’ criteria, the highest WELL, BREEAM, and LEED standards are offered predominantly among the prime office real estate sector and global corporations. Therefore, there is a real risk of mid-market commercial office space (a purpose-built office space caters to ‘hot-desking’ arrangements for employees from a range of different commercial organisations) or alternative workspaces that have been left out of the certification process despite the high standard of some of these properties. Additionally, the current COVID-19 related shift towards a greater need for more distributed workplaces is calling into question the expectation that the traditional office will be the biggest influencing factor in employee health and well-being and performance. The latest research has demonstrated the varied success of remote work during the COVID-19 pandemic. That also means that it may be worth examining the metrics that have traditionally been used to measure performance and employee engagement in light of these changes.
For example, a recent academic study of homework within the UK demonstrates that most work was carried out comfortably from home during the COVID-19 lockdown 
. In contrast to the academic research taken solely within the UK context, the XSF@home Total Workplace analysis elaborated by Cushman & Wakefield 
in the global context illustrates some greater concerns related to remote work during COVID-19. For example, 57% of respondents (EMEA countries) reported a lack of sense of well-being, 48% a lack of learning, and 55% struggled with connecting to the company culture of everyday staff engagement. Other industrial research conducted by Leesman 
demonstrates some differences in employee experience due to the variety of home working settings and work activities. This suggests a greater need for comparative analyses of both home/office workplaces to maximise employee experience in the future.
Both above studies highlight a greater need for flexible, hybrid workplace ecosystems in the future, balancing office and remote work. As already projected by Cushman & Wakefield 
, 50% of the workforce will likely be working across a ‘Total Workplace Ecosystem’, balancing office, home, and third places (e.g., café, library). Furthermore, despite remote work having been practised long before COVID-19 
, this current shift, which has been accelerated by the pandemic, may lead to more lasting effects on the organisation of work 
and management practices 
more broadly. It can be observed that since 2020 most academic research on work has been focused on remote work due to COVID-19 
. Considering this attention to the conditions of remote work, there is an equally emerging private sector interest in metrics that can effectively contribute to the monitoring of employee engagement remotely. However, employee engagement metrics traditionally do not consider the role of the built environment because they are primarily focused on evaluating social relationships in the workplace.
As outlined above, the link between the physical workplace and employee engagement remains understudied. However, some studies—although limited—report the importance of factors that may link employee engagement with the physical workplace environment, such as individual preferences 
, flexible work arrangements 
, or employee health and well-being conditions 
. For example, different workspaces may provide greater opportunities for individual arrangements and the control and support of employee engagement (e.g., access to green space to ensure cognitive refreshment and workplace exercise).
Figure 1 identifies the relevant research streams on the link between employee engagement and the physical workplace environment, to be further explored in the context of a post-COVID-19 workplace ecosystem scenario. Notably, most of the research on the physical workplace environment is investigated by the field of environmental psychology. Hence, more interdisciplinary research with other disciplines (e.g., occupational health, human resources/management, and organisational psychology) can potentially shed new light on this relationship and make it more holistic and explanatory. For example, there is a greater need for new studies on both indoor and outdoor environments, and the extent to which employee engagement varies between these different environments for different workplaces (e.g., the role of healthy communities, access to green space, availability of sustainable infrastructure, quality of residential sector, satellite offices’ location, etc.).
The academic approach for employee engagement.
Hence, further research is needed to explore employee behaviours conducive to better engagement (e.g., recovery experience) considering various types of physical workplace environments and managerial practices. For example, Figure 1 demonstrates that the role of work stress recovery is not addressed in typical environmental psychology work. Additionally, health and well-being must be a transdisciplinary consideration considering the extent to which it may be informed through recovery. Hence, positioning a definition of the ‘workplace’ within the context of a new post-COVID-19 workplace ecosystem may help to better explain the actual role of these factors.
2. The New Workplace Ecosystem: Implications for Monitoring Employee Engagement Post-COVID-19
Academic definitions of employee engagement differ from those elaborated by industry organisations across the ‘grey’ literature 
, resulting in numerous approaches to measuring engagement effectively. Nevertheless, one of the most cited academic definitions of employee engagement was proposed by Kahn 
as ‘the harnessing of organisation members’ selves to their work roles; in engagement, people employ and express themselves physically, cognitively, and emotionally during role performances’ 
(p. 694). Employee engagement also has been defined as ‘a positive, fulfilling, work-related state of mind that is characterised by vigour, dedication, and absorption’ 
(p. 74), one step up from commitment 
, a passion for work 
, or a ‘positive work-related psychological state characterised by a genuine willingness to contribute to organisational success’ 
(p. 5); a relationship with employee work, role and organisation, or ‘a state of mental energy’ that is ‘associated with involvement, commitment, passion, focused effort and energy’ 
In the field of organisational psychology, there are numerous metrics focused on employee engagement that have some relevance for employee health and well-being. For example, the Utrecht Work Engagement Scale (UWES) uses ‘vigour’ as one out of three proposed subscales to measure engagement. As ‘vigour’ can be defined as either strength, energy or enthusiasm 
, it can be logically linked with employee mental and physical health conditions, which constitutes the efforts around healthy workplace design (both sociologically and physically). Moreover, the UWES methodology is commonly used in various studies on the association between employee engagement and health outcomes 
. Additionally, linking employee engagement with human health at the workplace can ‘empower the workforce and sustain their well-being’, as highlighted in Deloitte’s model 
in the context of ‘adaptive workplaces’ in a post-COVID-19 scenario. However, this approach demands further investigation of the relationship between the physical workplace environment and employee engagement and a closer look at the metrics subsequently developed by both academics and industry, particularly for workplaces that aim to promote health and well-being.
The more distributed workspaces and the acceleration of remote work patterns in a post-COVID-19 world are expected to have a greater impact on employee flexibility associated with employee engagement 
, which may differ across a variety of workplaces. Additionally, employees will have the privilege of choosing their preferred workplace within such an ecosystem based on, for example, individual-level engagement. Hence, there will be a greater role of employee decision-making in the shaping of ‘adaptive workplaces’. As little is known about how different workplace settings in the ‘total workplace ecosystem’ impact employee engagement, further research is needed to address the whole spectrum of workplaces to thoroughly examine this issue.
Although there is no scientific evidence that a ‘healthy’ workplace design (e.g., WELL-certified office space) directly contributes to employee engagement, some studies report that both physical and mental health factors have a positive relationship with engagement 
(it has to be noted that WELL includes policy, design and maintenance features, but this paper focuses on the design side). However, there are many overlapping factors influencing engagement; so, it is hard to pinpoint which factors influence engagement, as well as how to measure it 
. Is it the access to natural light or the ability to rest that influences the outcome? Or is it management? Or is it both? The evidence is still emerging and needs clarity on which factors influence what and the extent of their interaction.
Given the fact that employee engagement is driven by a variety of factors (e.g., social relationships at the workplace), enhanced employee mental and physical health conditions can potentially mitigate the negative impact of other factors determining engagement at the workplace. For example, employee engagement as a concept in literature is often referred to as both a healthy workplace 
and employee health and well-being 
. Hence, a ‘healthy’ workplace can be understood holistically as a ‘healthy’ social and
physical environment. Nevertheless, there is now a greater need to investigate the role of employee behaviours (e.g., health-oriented ones, see Jindo et al. 
), and the organisational practices of ‘empowering workforce [employees] and sustaining their well-being’ in a variety of ‘adaptive workplaces’ 
—not to mention their contribution to engagement. The managerial aspect of these roles can be even more challenging considering the projected dominance of remote work patterns in the future.
To sum up, this section demonstrates that the construct of engagement has been strongly conceptualised on the organisational level (e.g., psychological states, job design, leadership, organisational and team factors, and organisational interventions) 
. Although the qualities of the physical workplace environment and their potential impact on general employee performance have been widely studied in the built environment field, these investigations have been limited to the traditional office environment 
. Given the above discussion of a new post-COVID-19 workplace ecosystem scenario, traditional office environment-based assumptions of employee engagement need to be reconsidered. For example, Kahn 
argued that ‘personal engagement’ with work is determined by experiences within the working environment.