A framework to support the design of a regenerative indoor environment

A framework to support the design of a regenerative indoor environment Lorenza Pistore 1 *, Thaleia Konstantinou 2 *, Wilmer Pasut 3 , 4 and Emanuele Naboni 5 , 6 , 7 1 R2M Solution s.r.l, Pavia, Italy, 2 Department of Architectural Engineering and Technology, Delft University of Technology, Faculty of Architecture and the Built Environment, Delft, Netherlands, 3 Department of Environmental Sciences, Informatics and Statistics, University of Venice, Ca’Foscari, Venice, Italy, 4 Department of Architecture, Korea University, Seoul, Republic of Korea, 5 Department of Engineering and Architecture, University of Parma, Parma, Italy, 6 Institute of Architectural Technology, Royal Danish Academy, Copenhagen, Denmark, 7 Anita Lawrence Chair in High Performance Architecture, School of Built Environment, University of New South Wales, Sydney, NSW, Australia In recent decades, a new generation of “green indoor”spaces has fulfilled the latest regulations and guidelines for a carbon-neutral society. Their targets are reachable through certifications embracing sets of measures and the adverse effects on occupants. Notwithstanding this, it has constituted a significant step forward in building design. However, the challenges given by climate change and the ecological crises lead to the need for new disruptive approaches to indoor design and function, enhancing human health and adopting regenerative design” at the forefront of buildings’conception. Besides the positive energyperformance attributes, the creation of a Regenerative Indoor Environment utilizes appropriate construction technologies and systems, to reinforce human health, and enhance users’experience. This regenerative paradigm shift foresees putting ecosystems at the centre and the users’psycho-physiological wellbeing, thus magnifying their collaboration. Despite regenerative design gaining some attention, a framework towards its implementation promoting the actual performances of the indoor environment is still missing, and designers do navigate among guidelines with no apparent performance indicators to be achieved, technologies to be implemented, or methodologies for postoccupancy evaluations. These three levels, constituting a stepwise methodology, are addressed by the authors within the sections of this paper, and validated as an example of the office buildings’typology. i) What characterizes a Regenerative Indoor Environment? ii) What technical solutions underpin the realization of a Regenerative Indoor Environment? iii) What methods or standards are crucial for its evaluation? With these premises, the paper contributes to supporting the creation of a regenerative indoor’design, by sampling and outlining regenerative indoor performances to be obtained, describing the adequate tools to implement them, as well as by displaying approaches and solutions for their final verification. KEYWORDS regenerative design, regenerative indoor environment, key performance indicators, technologies, post-occupancy evaluations OPEN ACCESS EDITED BY Song Pan, Beijing University of Technology, China REVIEWED BY Roberto Alonso González-Lezcano, CEU San Pablo University, Spain Claudio Martani, Purdue University, United States *CORRESPONDENCE Lorenza Pistore, [email protected] Thaleia Konstantinou, [email protected] RECEIVED 18 May 2023 ACCEPTED 04 December 2023 PUBLISHED 20 December 2023 CITATION Pistore L, Konstantinou T, Pasut W and Naboni E (2023), A framework to support the design of a regenerative indoor environment. Front. Built Environ. 9:1225024. doi: 10.3389/fbuil.2023.1225024 COPYRIGHT © 2023 Pistore, Konstantinou, Pasut and Naboni. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Frontiers in Built Environment frontiersin.org01 TYPE Methods PUBLISHED 20 December 2023 DOI 10.3389/fbuil.2023.1225024 1 Introduction In the last decades, “green”buildings have spread widely, offering an environmental performance higher than average buildings. When it comes to newly constructed buildings, “green indoors”are currently relatively common (Edwards and Naboni, 2012), and green buildings’certification tools are often characterized by a set of Key Performance Indicators (KPIs) accessible and achievable. As a result, the adopted design, often branded as “green”or “eco-friendly,”has led to a broad market transformation. Nevertheless, these buildings primarily aim to reduce the negative impacts on the environment and humans (Cole, 2012). However, in this historical period, with climate change emerging as one of our age’s most pressing and transformative challenges, the traditional approaches to sustainable building design are found lacking. These approaches focus on energy efficiency, resource conservation, and reduced carbon footprints. While these aspects are undeniably critical, they only address a fragment of the larger, intricate puzzle of global environmental change. Ecosystems, for instance, are vast interconnected webs of life, that provide essential services like water purification, crop pollination, and carbon dioxide sequestration. Simplified “green”building practices might not account for local ecosystems, potentially disrupting habitats or the larger environmental balance in the area. Biodiversity, another pillar of a healthy environment, is threatened globally, with species extinction rates soaring. A building that is energy-efficient but located in a biodiversity hotspot, for example, can contribute to habitat fragmentation or loss, undermining the very purpose of its “green”label. Lastly, human health, an intricate combination of physical, mental, and emotional wellbeing, encompasses everything from exposure to natural light, which can regulate our circadian rhythms, to the need for green spaces and natural views, known to reduce stress and promote mental health. The auditory environment, air quality, and even the materials we meet, all influence our health in subtle and profound ways. Therefore, in an era where the complexities of climate change demand comprehensive solutions, a mere focus on energy efficiency or carbon neutrality is insufficient. A holistic perspective that encompasses the intricate interplay between ecosystems, biodiversity, and the multi-faceted aspect of human health is imperative to truly address the challenges we face. It is becoming clear that buildings need to go beyond the mere reduction of their environmental impacts and should aim at positive environmental benefits. While current sustainability practices focus on moving from the conventional practice of degeneration to a neutral impact, regenerative design aims at allowing human and natural ecosystems to evolve (Figure 1). To respond to these issues, in the 1970s J.T. Lyle pioneered the term regenerative design (Lyle, 1994). To improve Reed and R. Cole creating definitions and showing their application. The topic of regenerative design has gained importance, and it is applied in several fields linked to various disciplines. However, a body of research focused on the design of a regenerative indoor is still missing, whereas there is an increasing application of the concept of regenerative design within research that is related to the built environment. Revisiting a broader definition (Naboni et al., 2019), a Regenerative Indoor Environment (RIE) is defined as an approach that aims to create a new set of relationships that reinforce the state of human health and natural ecosystems, utilising appropriate construction and technology targeted to indoor environments. In this perspective, the publication “Regenerative design in digital practice”(Naboni et al., 2019), presents an overview of the regenerative thinking, putting ecosystems at the centre (Ecological gain), together with the users’psychophysiological wellbeing (Salutogenesis), to the final extent of magnifying their collaboration (Biophilia). Their definitions are proposed hereafter. -Ecological gain. Instead of minimizing the negative impact of buildings on nature, regenerative design aims to design indoor spaces so that nature -including humansis connected to them and they can co-evolve: every building should be considered an equivalent dynamic organism that harmoniously gives and takes from the environment, adding value to it. In this way, restoring the ecosystem capital is also a benefit to occupants. FIGURE 1 Conceptual path from conventional to regenerative practice in buildings’design and operation. Adapted from (Brown et al., 2018). Frontiers in Built Environment frontiersin.org02 Pistore et al. 10.3389/fbuil.2023.1225024 -Salutogenesis. The term, invented by A. Antonovsky, means “generation of health”(Naboni et al., 2019) and, in this direction, the salutogenic focus is on making wellbeing part of the regenerative paradigm rather than the reductionist approach of sustainable design that targets the absence of ill health. Health-promoting environments are the new target and, as stated by J. Golembiewski, “Simple concepts like comfort, joy and aesthetics [...]”become “[...] the psychological bricks and mortar of all healthy buildings” (Golembiewski, 2012). -Biophilia. Highlighting the innate human relationship with nature, it is “the theory, science, and practice of creating buildings inspired by nature, with the aim to continue the individual’s connection with nature in the environments in which we live and work every day”(Kellert et al., 2011). In this realm of sustainable design, indoor environments have typically focused on achieving baseline levels of comfort and health. This has often translated to minimum ventilation requirements to maintain adequate Indoor Air Quality (IAQ), ensuring thermal comfort through Heating, Ventilation, and Air Conditioning (HVAC) systems, and providing energy-efficient artificial lighting to compensate for potentially insufficient daylight. While these interventions are undoubtedly beneficial, they operate on a paradigm of “do less harm.”The energy conservation efforts, in this respect, have primarily centred around minimizing consumption—be it through efficient appliances or reducing wastage. The recurrent concept of an indoor environment results from a design and construction process meant to create a space for human beings adequate to satisfy specific needs. Regenerative design, however, reconceptualises the indoor environment. Here, indoor spaces are not just habitats; they are ecosystems. In a regenerative paradigm, ensuring IAQ goes beyond reducing pollutants to actively revitalizing the air. This could be achieved through advanced biophilic integrations, where indoor plants play a role not just as aesthetic elements but as active air purifiers, or through architectural innovations that facilitate better natural ventilation, reducing dependency on mechanically conditioned air and thus conserving energy. Thermal comfort, too, evolves in its definition. This approach can create indoor environments that consume less energy and provide enhanced thermal comfort through passive means. This intricate process of “making an indoor environment”must deal with the technologies and with a selection process. Here, the driver consisted in the statement that proper technology solution sets can enable a Regenerative Indoor Environment for building users and key technologies have a pivotal role in promoting a paradigm shift in building design from “less bad”to “more regenerative.”Solution sets should be meant to be resilient against the contextual dynamics, and at the same time, balanced between positive effects on the indoor environment and the use of natural sources and energy. As underlined in (Lollini and Pasut, 2020), technologies must guarantee regenerative buildings, as well as bio-aesthetics (enlivening happy and healthy people in different contexts), with favourable environmental (e.g., energy) and social impacts. By definition, the concept of a regenerative indoor is harmonized in the contest, so the amount and types of resources needed for the technology must be sourced according to circular principles. There are a few regenerative design frameworks that attempt to embrace such a broader approach to the building design (e.g., The Living building Challenge at https://living-future.org/lbc/), The WELL Building Standard at https://www.wellcertified.com/), and many standards and guidelines have been released. All these sources prescribe performance indicators to be met, and for each indicator a value is recommended. These parameters and values differ one from another and guidelines are often controversial; thresholds are often targeting sustainable rather than Regenerative Indoor Environments, and designers have no clear framework to follow. Despite regenerative indoors being currently a common goal for many building standards and green-rating systems, a comprehensive framework to design buildings promoting health, wellbeing, highquality indoor conditions, and kinship to nature’s tangible outcomes, is yet to be achieved. Basic principles need to be linked with real performance, new targets, development, and assessment of innovative technologies. In this direction, a framework has necessarily to start defining the aspects that make an indoor environment regenerative for its users so that, in a second phase, the technologies, with their characteristics, can be selected to cover specific regenerative needs, and ends with a methodology for its post-occupancy assessment. In addressing the gap in regenerative indoor design, this paper seeks to elucidate regenerative indoor performances and provide designers with the appropriate tools for their execution. Central to this discourse is the overarching research question: how can designers render Regenerative Indoor Environments? The paper delineates three sub-questions to deepen our exploration: i) What characterizes a Regenerative Indoor Environment? ii) What technical solutions underpin the realization of a Regenerative Indoor Environment? iii) What methods or standards are crucial for its evaluation? Collectively, these questions form the bedrock of our methodological framework, serving as an explanatory outline and a guiding trajectory for designers navigating this field. 2 Aims and objectives The paper is meant to support practitioners in implementing forward-thinking regenerative design by setting a framework for conscious selection of technologies within a comprehensive decision-making process. In this direction, the three main research questions provide practical answers for designers and are unfolded in the different chapters of this paper. This first phase of the work has developed a methodology to characterize a Regenerative Indoor Environment (RIE) and has validated it by focusing on office buildings. The choice of this building typology relies on the fact that the intrinsic characteristics of such facilities include all the aspects that can be then extended and adapted to other building types. Our investigation is guided by three foundational questions, each one correlating to a primary objective, in order to understand the nuances of Regenerative Indoor Environments. Each question serves as a milestone, charting the path from conceptualizing a Regenerative Indoor Environment to its realization and subsequent evaluation. Frontiers in Built Environment frontiersin.org03 Pistore et al. 10.3389/fbuil.2023.1225024 i) What characterizes a Regenerative Indoor Environment? The inception of this inquiry does not merely seek a definition but a comprehensive understanding of RIE. Key Performance Indicators (KPIs) are crucial in this exploration. While they do not provide a standalone definition of RIE, they serve as essential metrics, setting regenerative thresholds. KPIs are designers who navigate the complex terrain of crafting spaces promoting health and wellbeing without sidelining the goal of building system energy efficiency. The latter is not the centre of the paper but will be mentioned when relevant. ii) What technical solutions underpin the realization of Regenerative Indoor Environment? With the attributes of RIE and their respective KPIs, we approach this question by examining the technological and design strategies that can facilitate such an environment. This stage is an intricate matter of innovation and integration. It mandates the interplay between various building sub-systems, ranging from construction techniques and spatial configurations to nuanced operational controls. Each element, in this mosaic, is geared towards echoing and amplifying the regenerative design ambitions. iii) What methods or standards are crucial for its evaluation? The embodiment of a regenerative space prompts another pertinent inquiry: its effectiveness. Evaluating an RIE necessitates a blend of post-occupancy analyses and experiential feedback. Objective methodologies juxtapose with subjective evaluations to gauge the building’s performance against the established KPIs. Postoccupancy evaluations (POEs) are critical in this phase. POEs are vital instruments that refine and recalibrate design and operational strategies, foregrounding occupant comfort, satisfaction, health, and wellbeing. 3 What characterizes a Regenerative Indoor Environment? Key Performance indicators for its definition and assessment As a primary driver of a Regenerative Indoor Environment is to demonstrably enhance occupants’comfort and wellbeing, it is pivotal to implement a holistic approach that considers multiple aspects connected with the human-building co-existence and interactions. Focusing on office buildings, as stated in (Bergs, 2002), indoor environmental quality conditions in such facilities can affect occupants’productivity to a high degree and impair the performance of different tasks and activities. According to (Wyon and Wargocki, 2013), workers’general wellbeing and health, and consequently productivity and performance, are affected by quality of indoor spaces, thermal, visual, acoustic and Indoor Air Quality (IAQ) aspects, as well as availability of personal control (Fisk, 2002; Fisk et al., 2011). Different typologies of discomfort issues have the power to invalidate task-related capabilities, to the final extent of severely long-term adverse health effects (Edwards and Naboni, 2012). Indoor Air Quality and thermal comfort are recognized to be the main responsible for a worsening in productivity (Wargocki and Wyon, 2017), which implies a loss in levels of attention and a subsequent increase in cognitive effort, significantly impacting decision-making, information processing and writing capabilities. Such aspects can also lead to ill health symptoms (Wyon, 2004;Lan et al., 2011). Del Ama Gonzalo et al. (ref) performed an assessment of IAQ in residential buildings, revealing that for the 25% of a specific timeframe, the surveyed occupants were exposed to potentially hazardous concentration levels of CO 2 , i.e., above 1,000 parts per million (ppm). Van Tran et al. (Tran et al., 2020), in their work, provide a critical review and assessment of the major sources of pollutant emissions, pointing out their health effects and issues related to sick building syndrome (SBS) and building-related illness (BRI). In addition, the work summarizes strategies for controlling and reducing pollutant concentrations, highlighting advantages and potentials. Besides thermal and IAQ features, which are usually the most considered, the visual environment is a key aspect in office spaces, due to its importance for conducting desk and screen reading tasks, as well as for its connection to wider psychological aspects like visual privacy. In this direction, the overall working experience can be enhanced by a good space layout design (Webb, 2006;Konstantzos and Tzempelikos, 2017), as also highlighted by the increasingly fundamental role that the visual environment is gaining in design and verification protocols (Court, 2010). According to (Heschong Mahone Group, 2003;Blume et al., 2019), the presence of windows with a view to the outdoors, an aspect that is often neglected or poorly considered, could enhance occupants’productivity even if only by an improvement of their psychological mood, mind wellbeing and, nonetheless, by a better regulation of circadian rhythms due to the exposure to natural daylight. To investigate the contribution of daylight to occupants’comfort, Hosseini and Ansari (Hosseini and Ansari, 2022) performed a daylight assessment of visual and non-visual effects of light shelves as daylight redirecting systems to enhance indoor daylight conditions, including the effects on circadian stimulus, visual comfort, and task performance. The study pointed out that the enhancements were minor compared to a conventional window. In another work, Moyano and al. (Moyano et al., 2020). investigated the potential hazardous effects on the retina given by blue light from artificial lighting sources. The results showed that, despite the blue light emission of the measured devices did not show high values that should be a cause for concern for eye diseases, the levels could influence circadian rhythms and sleep quality. Finally, acoustic performance of indoor spaces is another important feature. Acoustic conditions are often associated with individual health and wellbeing issues, as reported in (Lee and Aletta, 2019), since they directly impact on auditive effort, sound privacy, communication, and task performances. High psychological distress for office workers is stated to be linked to acoustical discomfort, resulting from co-workers’presence-related noises, lack of privacy, but also outdoor noises or in-space system noises. Workers are found to be irritated or distracted by the background noises in their workplace, e.g., noises coming from heating/cooling and ventilation systems, which can hinder their activities. For example, in (Karmann et al., 2017), the authors present IEQ survey results from 60 office buildings located in North America, including the comparison on acoustic satisfaction between radiant and all-air systems. In (Moyano et al., 2022), the possible effects on health of ultrasound exposure in working environments were reviewed, pointing out the necessity of more investigation studies on the ultrasound emissions that can be Frontiers in Built Environment frontiersin.org04 Pistore et al. 10.3389/fbuil.2023.1225024 absorbed by the human body and how this can affect humans. In addition to this, both poor visual and acoustic conditions are demonstrated to potentially result in visual and acoustic pathologies, which can also negatively aggravate psychological mood and working attitudes (Boyce, 2010;Park et al., 2018). With these premises, in (Pistore et al., 2023a) the authors identified and collected the multiple benefits that can, on the contrary, result from an improved new generation of buildings and indoor spaces. Despite their economic quantification is still research in progress, all these positive effects should be considered in an overall building performance evaluation. According to some preliminary quantifications, in (Fisk, 2002) reduced respiratory illness can account for productivity gains/annual savings around USD 6–14 billion, reduced allergies and asthma for USD 1–4 billion, reduced sick building syndrome symptoms for USD 10–30 billion, and worker performance can improve from changes in thermal environment and lighting for an estimation of USD 20–160 billion. In the EU CRAVEzero Project (CRAVEzero project 2020), an increase in productivity is the natural result of a decrease of health effects, especially when considering office environments, with reduced sick leaves estimated around 10% for and additional investment of 70 EUR/m 2 , and an estimated profitof 154 EUR/m 2 over 30 years. According to (Almeida et al., 2017) health benefits from improved indoor climate can be monetised as a permanent annual benefit to society around EUR 42–88 billion. The authors estimate that for an additional investment of 170 EUR/ m 2 , an increased productivity of +1% can be achieved, with a profit estimated over 30 years of around 347 EUR/m 2 . As the main objective of this work is to deliver a framework for the design and verification of RIEs, as a first step, a set of Key Performance Indicators (KPIs) for the indoor environment has been identified. Secondly, to each KPI, appropriate values and suitable thresholds were attributed after a proper review of the main documents and guidelines in the field, to provide designers with a comprehensive tool for the definition of a regenerative space. Considering the wellbeing theories’state-of-the-art over the past decades, four main conventional areas are generally considered and assessed in the context of indoor environmental conditions, i.e.,: air quality, hygro-thermal environment, visual environment, acoustic environment, which are recognized to affect both occupants’health and energy/costs demands. These aspects can be assessed through objectively measured indoor parameters and users’subjective responses, which are both equally significant and to be integrated in a robust overall Post-Occupancy Evaluation (POE) of indoor conditions (Zhang and Altan, 2011;Heinzerling et al., 2013;Pei et al., 2015;Leccese et al., 2021;Mujan et al., 2021). Regarding the verification of indoor conditions, national and international standards report indicators and thresholds to be fulfilled both for objective and subjective methodologies. However, often different guidelines contain different requirements and values for the same environmental aspect, and this leads to an uncertainty that complicates the navigation of such regulations, the interpretation of specifications, and does not allow generalization and real standardization. The result is a generalized controversial understanding of the required performance levels among professionals. To delineate a structured framework for the fulfilment of a Regenerative Indoor Environment, a stepwise methodological approach was outlined referring to office buildings. The final goal was to provide a structured and repeatable tool, easily expandable to other building typologies, to be efficiently implemented in everyday practice for the design and evaluation of a RIE. As a first step, the office building environment was characterized using important environmental aspects and sub-aspects to be taken into consideration. After this identification, a literature review on state-of-the-art standards and thresholds currently applied was conducted. Results are presented in Table 1. As it can be observed, to fulfil the initial aim and definition of a “regenerative”design, some human-nature related values were included besides the environmental aspects, which are key not only to preserve, but also to boost occupants’satisfaction levels, health, and wellbeing. External view and right to light, together with biophilia and access to nature, were considered, to embed new potentialities to IEQ and create inspiring indoor environments. In fact, during the 21st century, one major issue resulting from artificial environments was the subsequent disconnection between nature and people. Current common design approaches usually fail in providing breakthrough solutions to the problem, since they perpetuate an anthropocentric design and thus the human-nature dichotomy. On the contrary, building’s technologies should consider all habitats’needs, and lead to a significant improvement of occupants’wellbeing by reconnecting their bond with other forms of life through exposure to natural elements (Browning et al., 2014). According to the key aspects highlighted in Table 1, a list of KPIs was proposed to promote the creation of a Regenerative Indoor Environment that overcomes the limited concept of a merely sustainable building, but to achieve conditions that improve occupants’experiences, health, wellbeing, attitudes, and psychological mood. The approach conducted to draft this list of KPIs has consisted neither of nullifying nor of erasing the regulatory requirements, instead, it has been intended as a step forward towards the achievement of a better indoor environment and reconnection with natural elements. A total of 10 KPIs were proposed, considered as the main aspects to be addressed, and for each KPI a regenerative threshold was decided. Results are shown in Table 2. Specific values were determined after an accurate evaluation of the ones gathered in the state-of-the-art documents reported in Table 1, aiming at clarifying the controversy of different sources proposing different thresholds and finally embrace an overall new perspective. For each KPI in Table 2,adefinition is introduced hereafter. 3.1 Air quality environment O. Fanger in his paper “What is IAQ?”(Fanger, 2006), stated that: “A paradigm shift is required, and further future shifts are foreseen where we learn how to make indoor air equally fresh and pleasant as outdoors when it is best.”In this perspective, three KPIs were selected regarding this environmental aspect, i.e., formaldehyde, PM 10 and PM 2.5 . According to the United States Environmental Protection Agency (EPA, 2023; United States Environmental Protection Agency, 2023), formaldehyde is defined as a colourless and potentially flammable gas at room temperature. Occupants exposed to this chemical hazard may manifest different health issues, lie skin, eyes, Frontiers in Built Environment frontiersin.org05 Pistore et al. 10.3389/fbuil.2023.1225024 throat, and nose irritation. A prolonged time of exposure may lead to cancer. In buildings, primarily, people are exposed to it by breathing air with off-gassed formaldehyde, coming from resins used in wood products, building materials, insulation, household and paper products. According to the World Health Organization (WHO) (World Health Organization, 2020), a short-term exposure of 0.1 mg m −3 is associated with throat and nose irritation in humans, but sensible targets can sense its presence also at lower concentrations. With these premises, an air-quality guideline value of 0.1 mg m −3 is recommended as a 30-min average, to avoid any significant sensory irritation in the average population. PM 10 (United States Environmental Protection Agency, 2023) consist in particles that are smaller than 10 microns in diameter and exposure to high concentrations of them in the air can irritate the eyes and throat. PM 10 particles can be generated by sea salt, pollen, and combustion activities such as motor vehicles and industrial processes in general, but also mainly by dirt roads. In people with existing heart or lung diseases, e.g., asthma and other breathing TABLE 1 Framework for characterization of the indoor environment: state of the art analysis. Building environment State of the art Aspects Sub-aspects Main current literature sources and standards Air quality - Outdoor/indoor ventilation - EPA, National Ambient Air Quality Standards (U.S. Environmental Protection Agency, 2023) - Chemical/natural contaminants - WHO, Air Quality Guidelines for Europe (World Health Organization, 2020) - Concentrations - NIOSH, Pocket Guide to Chemical Hazards (U.S. National Institute for Occupational Safety and Health, 2020) - Odours - OSHA, Code of Federal Regulations (U.S. Occupational Safety and Health Administration, 2023) - Occupants’satisfaction - ANSI/ASHRAE, Standard 62.1 (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2022) - ANSI/ASHRAE, Fundamentals (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2021) - CEN, UNI EN 16798 (European Committee for Standardization, 2019) - IWBI, The WELL Building Standard (International Well Building Institute, 2016) - ILFI, The Living Building Challenge (International Living Future Institute, 2022) Hygro- Thermal - Temperature - ANSHI/ASHRAE, Standard 55 (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2020) - Humidity - CEN, UNI EN 16798 (European Committee for Standardization, 2019) - Local discomfort - CEN, EN ISO 7730 (European Committee for Standardization, 2006) - Occupants’satisfaction - ANSHI/ASHRAE, Fundamentals (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2021) - IWBI, The WELL Building Standard (International Well Building Institute, 2016) - ILFI, The Living Building Challenge (International Living Future Institute, 2022) Visual - Natural/artificial lighting - CEN, EN 12464 (European Committee for Standardization, 2021) - Glare - CEN, UNI EN 16798 (European Committee for Standardization, 2019) - Colour rendering - CIBSE, Daylighting and Window Design Guide (The Chartered Institution of Building Services Engineers, 1999) - Circadian rhythm - BRE, BREEAM (Building Research Establishment, 1990) - Occupants’satisfaction - USGBC, LEED (U.S. Green Building Council, 2021) - Daylighting, Artificial Lighting and Non-Visual Effects Study for a Residential Building (Mardaljevic et al., 2012) - IWBI, The WELL Building Standard (International Well Building Institute, 2016) - ILFI, The Living Building Challenge (International Living Future Institute, 2022) Acoustic - Background noise level - CEN, UNI EN 16798 (European Committee for Standardization, 2019) - Sound Absorption/reflection - IWBI, The WELL Building Standard (International Well Building Institute, 2016) - Reverberation - Other national standards and regulations - Acoustic insulation - Occupants’satisfaction Human-Nature - External view and right to light - IWBI, The WELL Building Standard (International Well Building Institute, 2016) - Biophilia and access to nature - ILFI, Living Building Challenge (International Living Future Institute, 2022) Frontiers in Built Environment frontiersin.org06 Pistore et al. 10.3389/fbuil.2023.1225024 problems, an increase in symptoms has been shown, leading to wheezing, chest tightness and difficulty breathing. PM 2.5 (United States Environmental Protection Agency, 2023) particles are smaller than 2.5 μm in diameter and can therefore be inhaled deeply into the lungs, which can lead to health problems, especially in children, people over 65, pregnant women and people with existing heart or lung diseases. These particles result from the combustion of fossil fuels, organic matter, and most other materials such as rubber and plastic, and automobiles, power plant emissions, and bush fires are all major sources of fine particles. Symptoms may include wheezing, chest tightness, and difficulty breathing. Two types of national air quality standards are established in the Clean Air Act and the EPA’s 1990s amendments to the National Ambient Air Quality Standards (U.S. Environmental Protection Agency, 2023). Primary standards provide public health protections, including protection of the health of vulnerable populations such as asthmatics, children, and the elderly. Secondary standards provide protections for the common good, including protection from reduced visibility and damage to animals, plants, crops, and buildings. Primary requirements were selected for the scope of this work aiming at a RIEandlimitvaluesoflessthan150μgm −3 for PM 10 were set, averaged over 24 h, and not exceeded more than once a year on average over 3 years; less than 12 μgm −3 for PM 2.5 in annual average, averaged over 3 years. 3.2 Hygro-thermal environment The ANSI/ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2020)provides the methods to be followed for the evaluation of thermal comfort conditions in accordance with the type of environment, integrated HVAC system and ventilation type. Recommended values are to comply with this standard. While the ANSI/ ASHRAE Standard 55 in a sustainable approach aims to maintain conditions that preserve comfort, the regenerative interpretation of the same standard seeks to transform and elevate those conditions to spaces that are not just comfortablebutarealsohealth-generating. It suggests evolving from a reactive stance, which addresses discomfort once it arises, to a proactive stance, which anticipates and optimizes the environment for enhanced wellbeing, aligning the built environment more closely with its natural surroundings and the inherent needs of its inhabitants. To this extent, the trend of creating constant, comfortable indoor environments in buildings is today considered not healthy. Over-reliance on such environments weakens humans’ability to handle temperature changes and can harm health. Instead, allowing more temperature variation indoors can and improve human resilience and health (reduce CO 2 emissions, save resources (Pallubinsky et al., 2023). TABLE 2 List of KPIs for a Regenerative Indoor Environment and proposed regenerative values. Source (Lollini and Pasut, 2020, Table 8, p. 44). Environmental aspect Sub-aspect KPI Regenerative values Air Quality Contaminants Formaldehyde ≤0.1 mg m −3 [30 min] Environment Outdoor/Indoor Particulate matter: PM 10 <150 μgm −3 [24 h] PM 2.5 <12 μgm −3 [1 year] Occupants’satisfaction % satisfied people ≥80% a Hygro—Thermal Environment Temperature/humidity/ air speed Implementation of ASHRAE 55 ASHRAE 55 + evaluation of air movement Occupants’satisfaction % satisfied people ≥80% a Visual Environment Daylight Useful Daylight Illuminance 300–3,000 lux Circadian Rhythms Equivalent Melanopic Lux ≥200 (9a.m.-1p.m.) b Occupants’satisfaction % satisfied people ≥80% a Acoustic Environment Background noise level Noise criteria ≤30/≤40 c Occupants’satisfaction % satisfied people ≥80% a Human-Nature Environment Right to light % of workstations with windows’access to daylight 100% of inhabitants Connectivity to Nature (Biophilia) Intentional interior design interventions that bridge the gap between natural and built environments - Biophilic design workshop held prior to design - Biophilic interventions incorporated: 7/ 14 biophilic patterns Occupants’satisfaction % satisfied people ≥80% a a response rate representing at least one-quarter of the total number of building/indoor environment users. b for 75% or more workstations. c enclosed/open offices. Frontiers in Built Environment frontiersin.org07 Pistore et al. 10.3389/fbuil.2023.1225024 3.3 Visual environment In the domain of daylighting, regenerative design focuses on not just providing sufficient light, but ensuring that the light actively contributes to the wellbeing and health of occupants. The selection of the Useful Daylight Illuminance (UDI) (Nabil and Mardaljevic, 2005) as a Key Performance Indicator (KPI) embodies this philosophy. By gauging the annual occurrence of illuminances that lie within the 300–3,000 lux range on the work plane, the UDI ensures that natural light is harnessed to optimize visual comfort without resorting to excessive artificial illumination. This not only conserves energy but also creates spaces that are in harmony with their natural surroundings. The incorporation of the Equivalent Melanopic Lux (EML) (International Well Building Institute, 2016) takes this regenerative approach a step further. Rather than just measuring light in terms of visual utility, the EML quantifies how light impacts human health at a physiological level, specifically the melanopsin-encoded response, which is crucial for regulating our circadian rhythms. By aligning with the WELL Building Standard, the emphasis shifts from illumination to the holistic wellbeing of occupants, ensuring that daylighting strategies provide visibility, while actively contributing to the physical and psychological health of building users. 3.4 Acoustic environment Embracing the Noise Criteria (NC) as set out by the International Well Building Institute (International Well Building Institute, 2016) represents a marked shift towards a regenerative approach in indoor acoustic design. Unlike traditional strategies which simply aim to minimize or insulate against noise, the NC method actively shapes the acoustic environment. By assessing sound pressure levels and adhering to criteria curves across octave band spectra ranging from 63 to 8,000 Hz, the NC ensures that every frequency is accounted for, creating a balanced soundscape. What makes this approach inherently regenerative is its humancentric focus. Using the WELL Building Standard as a guide, specific thresholds have been chosen: a “confidential”speech privacy level with NC ≤30 for private offices, ensuring intimate conversations remain private, and a “normal”speech secrecy level with NC ≤40 for open-plan offices, which balances openness with acoustic comfort. These values not only reduce noise, but also cultivate an environment that actively supports the activities and interactions taking place within. By adhering to these NC values, the design not only mitigates potential acoustic disturbances but actively crafts an environment that promotes wellbeing, understanding, and effective communication. In this regenerative framework, noise is not merely a challenge to be addressed but an element to be sculpted, ensuring spaces not only sound good but feel good for their occupants. 3.5 Human-nature environment The awareness that humans and the built environment co-exist together within natural systems is a pillar of regenerative design, intending to restore ecosystems and allowing them to thrive and evolve along with the human system. This nature-environment- human connection is an intricate relationship reflecting the profound and inherent bond between humans and their natural surroundings. This connection has roots in evolutionary biology, where early humans evolved in close harmony with nature, leading to a deep-seated affinity towards natural environments—a concept termed “biophilia”by Edward O. Wilson (use same reference used above). This connection is not just aesthetic or romantic; it has tangible physiological and psychological impacts on human health and wellbeing. To enhance the connectivity between occupants and the natural environment, two KPIs were here selected. The percentage (%) of workstations with windows’access to daylight (International Well Building Institute, 2016)reflects results of research showing that access to daylight and exterior views increase mood and productivity in indoor office environments (Heschong Mahone Group, 2003). This indicator consists of the percentage of all workstations within a specified distance from an atrium or window facing the outside. To significantly enhance a regenerative space, its recommended value refers to the Well Building Standard, but it was decided to extend it to a total of 100%. Connectivity to nature can be measured using the visual connection to nature (Kellert et al., 2011) as a viewing factor from the workplace. This indicator is based on evidence from visual preference research, which suggests that the preferred view is looking down a slope to a scene that includes shady clumps of trees, flowering plants, calm non-threatening animals, evidence of human habitation, and clean water. The recommendations were adapted from (Browning et al., 2014). 3.6 Occupants’satisfaction The percentage (%) of satisfied people, determined from the subjective answers from the users, is meant to be rated for the five selected environmental aspects, i.e., indoor air quality, hygrothermal environment, visual environment, acoustics, and human nature. Despite a value of 100% of satisfied users is desirable, a share of occupants would most certainly never be satisfied due to the intrinsic personal nature of subjective responses. For this reason, we aim at a value that is 80% or higher (American Society of Heating Refrigerating and Air-Conditioning Engineers, 2020), with a response rate representing at least one-quarter of the total number of building/indoor environment users. It can be determined by handing out subjective questionnaires to building occupants during POE campaigns. In conclusion, using the percentage of satisfied users as a key metric embodies the essence of regenerative design by centring on human wellbeing, fostering continuous engagement, and emphasizing iterative improvement. 4 What technical solutions underpin the realization of a Regenerative Indoor Environment? Solution sets for building’s sub-systems Regenerative design, in its essence, surpasses mere sustainability by not only reducing harm but also by actively enhancing and restoring the environment it interacts with. In this context, the technologies and approaches selected should not only serve their Frontiers in Built Environment frontiersin.org08 Pistore et al. 10.3389/fbuil.2023.1225024 primary functional purpose but also contribute to the holistic wellbeing of the occupants, the self-sufficiency of the building, and a positive feedback loop with the surrounding ecosystem. This means that when considering technologies, it is not just about immediate utility but also about the long-term impact, adaptability, and the potential to foster a deeper connection between the occupants and their environment. The aim is to create dynamically responsive spaces, that grow and evolve, and that heal their inhabitants over time: this necessitates new types of building components. Building components, when viewed through a regenerative lens, embody qualities of being living, regenerative, restorative, and adaptive. “Living”components integrate biological elements, creating a symbiotic relationship between the built environment and nature. Biophilic design is an important aspect of this approach, as tamis can be pursued by the design of interiors inspired by nature and imbued with positive emotional experiences, to continue the individual’s connection with nature in the environments in which we live and work every day (Kellert et al., 2011). “Regenerative” elements actively renew and enhance resources beyond mere conservation. Regenerative features aim to reintroduce or lastly, “adaptive”components dynamically respond to evolving conditions, ensuring buildings remain resilient to climatic shift ensuring indoor thermal comfort (Romano et al., 2018). These components are pivotal to regenerative design because they transform structures from static entities into dynamic ecosystems, ensuring buildings not only coexist with nature but actively participate in nurturing and enhancing their occupant experience (Gambato and Zerbi, 2019). To discern the optimal technologies that align with the principles of regenerative design for indoor environments and to meet the stipulated KPIs, it is paramount to elucidate the interconnectedness between identified environmental facets and their nuanced sub-elements. This involves harmonizing these facets with the intrinsic functionalities of building systems, components, and their symbiotic technologies. Core to these functionalities are the modulation of air quality, thermal regulation and resilience, illumination and glare equilibrium, acoustic harmony and mitigation, and the integration of biophilic elements to foster holistic wellbeing (Konstantinou et al., 2020). In a regenerative framework, it is essential to recognize the interconnectedness of building components and their potential multi-functionality. Single technological solutions, when optimally leveraged, can serve more purposes. A regenerative design matches the internal conditions—encompassing a blend of ambient and surface temperatures, humidity, and airflow reminiscent of natural outdoor settings—with avenues for personal agency over these conditions, whether through manual interventions, digital adjustments, or spatial reconfigurations (Browning et al., 2014). Realizing these functions necessitates the integration of technologies across the building’s various subsystems, enveloping the building shell, internal elements, and dynamic services and controls. Therefore, our solution spectrum adopts an integrated approach, interweaving environmental considerations, functions, and subsystems. In this integrative narrative, three predominant building subsystems emerge as focal points: i) the building’s envelope, ii) adaptive interior elements and finishes, and iii) the building’s active and responsive systems, inclusive of HVAC, RES, and control mechanisms. 4.1 Building envelope The building envelope is one of the main building components to regulate the indoor environment (Konstantinou et al., 2020) and is designed to fulfil multiple functions (Klein, 2013). Regenerative building envelopes can be defined as technological bio-based solutions, inspired by nature, adaptive, and capable of interacting with the external environment and user requirements to improve indoor comfort (Kuru et al., 2019). The regenerative building envelopes must be able to control one or more of the environmental aspects, as outlined in Table 1. For instance, they should prevent contaminants from entering from the outside, thus promoting good Indoor Air Quality, while also providing adequate thermal resistance to address the required hygrothermal performance. In addition, the openings of the building envelope affect the visual and the acoustic environment. Furthermore, these must positively influence health, wellbeing, and quality of life through building envelope solutions that follow the natural patterns and features. By following natural patterns and features, and considering biomimetic properties, regenerative envelope solutions have the potential to revolutionize product development and have biophilic and regenerative impact. A variety of regenerative envelope systems have already been developed, designed to react to changes in external factors and promote regenerative sustainability for the built environment. Adaption is key to achieve the regenerative impact on the indoor environment. Two main categories can be distinguished in such adaptive technologies: 1) adaptive technologies, which rely on passive design to improve indoor comfort and building energy efficiency, and 2) active technologies that include renewable harvesting (Mazzucchelli et al., 2018). 4.2 Interior elements and finishes Several scientific studies show that we spend most of the day inside the buildings where we work and live. Great attention must be paid to the design and selection of interior elements (materials and furniture), choosing natural and eco-compatible ones, to reduce the environmental impact of the built environment and to improve indoor comfort. In addition, to decrease users stress, it is important to create inside the building indirect experience, involving contact with nature that requires ongoing human input, such as views of the nature, shapes, forms, patterns, and colour palette that feels connected to nature, along with natural light, live plants, greenery, and water features. It has been shown (Appleton, 1996) that users react positively not only towards head-on exposure to the natural environment but also, they have responded with certainty to the artificial imitation of nature and its forms in fractal patterns, and cases of organic and conceptual mimicry of the natural entities. 4.3 Active building systems In the framework of regenerative design, thermal comfort must be achieved primarily through a proper control of thermal fluxes within the building envelope, and secondly through a well-designed and efficiently operated HVAC system (Konstantinou and Prieto Frontiers in Built Environment frontiersin.org09 Pistore et al. 10.3389/fbuil.2023.1225024 Funding This work was conducted within the European Cooperation in Science and Technology COST Action CA16114 RESTORE. Acknowledgments The work presented in this paper is part of the COST Action RESTORE WG4. The authors would like to thank all the COST Action Participants, who have contributed to the work, particularly Roberto Lollini (co-leader of WG4), Francesco Fiorito, Rosa Romano and Antonia Sore who contributed to the development of the Repository of Regenerative Technological Solutions, and Martin Brown for his precious insights on the KPIs regarding the human-nature relationship and biophilic aspects. Conflict of interest Author LP was employed by R2M Solution s.r.l. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Publisher’s note All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. 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