Sustainable Built Environments and Cities: Connecting Climate Resilience, Resource Efficiency, Human-Centered Design, and Digital Innovation

Buildings and cities are now at the heart of climate and resource transitions. They account for a major part of energy demand, material use, greenhouse gas emissions, and waste generation, while also shaping people’s exposure to heat and other environmental stresses. The built environment offers concrete opportunities of mitigation and adaptation as well; options for urban form, envelopes, materials, energy systems, controls, and maintenance can influence performance for several decades.

For this reason, recent global assessments have moved gradually beyond considering only operational energy savings method and now place greater attention on carbon emissions over an entire lifecycle, resilience, circular material flows, and the quality of indoor and outdoor environments [1,2,3].

This broader scope is also visible in recent regulatory and assessment frameworks. The recast European Energy Performance of Buildings Directive strengthens the effort towards a stock of buildings with zero emissions, while Level(s) and guidelines on the total lifecycle carbon impact guidance aim at a common and efficient evaluation of resource use and lifecycle impacts [4,5,6]. At the same time, sensing technologies, cloud platforms, digital twins, artificial intelligence, and predictive analytics are transforming the way buildings and energy systems are managed.

However, technical capability by itself is not enough. In many cases, performance gaps result from incomplete data, poorly applied commissioning, insufficient maintenance, weak consideration of occupants, and poor feedback between design and actual operation. Another difficulty is that solutions developed in one climatic or institutional setting are not always easy to transfer elsewhere.

It was within this context that the Special Issue “Sustainable Built Environments and Cities: Innovations in Energy, Materials, and Control Systems” was launched with the intention to provide an interdisciplinary space where technological innovation could be discussed, together with environmental responsibility and human well-being. The original scope was deliberately broad, covering low-carbon materials, renewable-energy integration, intelligent control, indoor environmental quality, digital twins, lifecycle assessment, circularity, passive design, and climate-resilient urban planning.

Of course, four published articles cannot cover all these topics. Nevertheless, they provide four focused and complementary views of how sustainability is translated into concrete actions at different levels of intervention: that of material, building, infrastructure, and urban (Contributions 1–4).

The first paper, by Díaz-López et al., looks at climate-resilient schoolyards not simply as greening projects but as a form of distributed public infrastructure that can support urban cooling, stormwater management, biodiversity, education, social interaction, and environmental justice (Contribution 1).

Based on a comparison of nine international programs, the authors highlight the feasibility of interventions like depaving, vegetation and shading, nature-based drainage, and the selective use of cool materials. What makes this study particularly useful is that it moves the discussion beyond the simple question of whether a schoolyard is green or not. Instead, it considers how environmental and social functions can be designed together.

This study represents an interesting contribution since it goes beyond a simple “greening” analysis of schoolyards, as it proposes a multicriteria decision framework organized around environmental and climatic performance, social and educational equity, urban integration and accessibility, feasibility, and co-benefits. Its CAME (Correct, Adapt, Maintain, Explore) analysis indicates that many programs concentrate on correcting existing deficiencies and adapting sites, while long-term maintenance and systematic exploration of innovation receive less attention and are less consistently embedded [7]. This finding is consistent with the wider literature showing that schoolyard greening can support thermal comfort, physical activity, health, and child development; however, that outcomes depend on design, governance, maintenance, and community use [8,9,10].

The article thus reframes schoolyards as strategic nodes in neighborhood-scale adaptation, particularly in areas that are highly exposed to heat and lack public greenery. Importantly, the multicriteria decision framework is presented as a transferable structure to be calibrated locally rather than as a universal ranking model.

The second paper, by Sage and Fieldson, takes the focus from urban adaptation and moves it to material and resource efficiency with a study on cost and carbon consequences of construction waste in UK housebuilding (Contribution 2).

The authors use an interesting mixed-methods approach that combines a literature review, a retrospective analysis of three housing developments, and detailed monitoring of a four-bedroom affordable home during construction. Across the three completed developments, excess materials accounted for approximately 1% of the build cost per dwelling. The authors are careful not to present this value as a benchmark for the whole sector. Even so, it gives a useful indication of how small and often overlooked inefficiencies can accumulate when repeated across a housing program.

These findings could be particularly relevant in the social housing sector, where savings from improved estimation, ordering, handling, and waste management could be reinvested in additional delivery while simultaneously reducing embodied carbon.

The study complements broader work about the efficiency of material usage and the management of wastes from construction and demolition, which has highlighted inconsistent datasets, variable waste-rate assumptions, and the need to prioritize prevention over downstream recovery [11,12]. Its central message is pragmatic: decarbonization does not depend only on disruptive technologies. Indeed, better measurement and repeated marginal improvements in routine procurement and site practices can generate meaningful financial and environmental value.

At the scale of building operation, García-Fernández and Fernández Bonilla examine another gap highly relevant in the sustainable development of the built environment: daylight, LED lighting, energy performance, and user perception in university classrooms (Contribution 3).

The study brings together in situ illuminance measurements, climate-based simulation, lighting-energy assessment, and student surveys in Madrid. The existing LED systems of the assessed classrooms complied with current illuminance requirements, with lighting power density values ranging from 4.38 to 12.47 W/m². However, one interesting finding is that more daylight does not always mean better lighting. Depending on the orientation, geometry, windows, and surrounding obstructions, high daylight availability may also create glare, uneven conditions, and insufficient illuminance in the deeper parts of a classroom.

The estimated potential of daylight-responsive dimming and occupancy-based control is substantial, with electricity savings of 27–47% depending on orientation and daylight distribution. For the analyzed classrooms, this corresponds to approximately 2685 kWh per year and estimated reductions in carbon emissions of 110–239 kg CO₂ per classroom annually. User feedback also provides an essential contribution to the study. Indeed, 79% of respondents, among the building occupants, considered natural light beneficial to academic performance, yet glare control and visual-task clarity remained critical. These results align with the development of climate-based daylight metrics and research demonstrating that control strategies must reconcile energy savings with spatial quality, occupant behavior, and non-visual responses to light [13,14,15]. The conclusions strongly suggest the importance in moving the retrofit process beyond lamp replacement toward the integration of adaptive control combined with shading and user-centered evaluation.

The fourth contribution takes the discussion beyond buildings and considers the renewable-energy infrastructure that increasingly supports them. Franco-Miranda et al. present a multi-platform digital solution combining remote monitoring, sensor networks, cloud-based data acquisition, historical records, and predictive analytics for solar, wind, and hybrid systems (Contribution 4).

The platform bridges information into one environment and standardizes workflows for different user profiles, addressing a commonly encountered problem in industry: maintenance data are often scattered across separate tools, teams, and recordkeeping systems.

Based on collected data reports, the study highlighted a reduction of 30% in unplanned downtime and a 20–25% decrease in operating and maintenance costs, largely due to real-time visualization, automated parameter synchronization, proactive scheduling, and improved decision support and planning. The contribution is in line with the evolution from corrective and time-based maintenance toward condition-based and predictive strategies supported by stream processing and machine learning [16,17,18]. Importantly, the solution presented links digitalization to sustainability through its ability to extend asset life, limit unnecessary resource consumption, and improve reliability of renewable sources. Its future development toward digital twins, autonomous fault prognosis, demand response, and grid services illustrates that maintenance platforms can evolve from simple data management tools into active components of flexible energy systems [19].

Although the four papers deal with rather different subjects, several common lessons can be drawn from them. The clearest one is that sustainability is a whole-system property. Vegetation without maintenance, daylight without glare control, efficient products without material accounting, and renewable assets without reliable operation will not deliver the expected benefits for long. The focus should therefore move beyond individual components and consider the wider socio-technical system in which they operate.

Measurement is another issue that appears throughout the collection. The papers make use of multicriteria analysis, material records, environmental measurements, simulations, user surveys, sensors, and operational data. This variety is a strength because it combines numerical performance indicators with qualitative and contextual evidence. At the same time, definitions are not always consistent, records may be incomplete, systems do not necessarily communicate with each other, and monitoring periods are often short. These limitations make comparison and generalization more difficult. Shared data models and clearly reported assumptions would be especially valuable when results are used for benchmarking, procurement, policy, or machine learning applications.

The papers also remind us that users and communities are not external to performance. Students’ visual preferences, community access to schoolyards, everyday practices on construction sites, and maintenance decisions made by operators all influence the final outcome. Human-centered design should therefore be seen as part of performance itself and not as an additional consideration added at the end. Likewise, automated systems should remain understandable and should preserve privacy, an appropriate level of user control, and the possibility of manual override.

Transferability also requires local calibration. The schoolyard framework depends on climatic conditions, neighborhood vulnerability, governance capacity, and maintenance resources. Lighting outcomes depend on orientation, geometry, schedules, and climate. Waste practices reflect procurement arrangements and local supply chains, while digital maintenance platforms must accommodate different asset types, communication protocols, and organizational maturity. Future studies should distinguish clearly between transferable methods and context-specific parameter values.

Finally, lifecycle continuity remains a major gap. Research and policy often prioritize design intent or initial deployment, while maintenance, degradation, changing occupancy, climate evolution, and end-of-life recovery receive less systematic attention. The Special Issue contributions collectively show that long-term performance depends on closing the loop between planning, design, construction, operation, maintenance, adaptation, and eventual reuse or recovery.

These findings point toward several directions for future work. A first priority is to bring operational energy, embodied carbon, water, waste, resilience, health, and equity into more transparent whole-life assessment frameworks. Energy savings should not be evaluated separately from material consequences, maintenance requirements, or the way benefits and risks are distributed among different groups.

Longer-term validation across different contexts is also needed. Post-occupancy and post-implementation studies should examine whether the reported benefits remain over several seasons and years and whether they can be reproduced in different climates, socioeconomic settings, and organizational conditions. This is particularly important for nature-based solutions, adaptive lighting controls, and predictive-maintenance systems, whose performance may change as vegetation matures, occupants adapt their behavior, sensors drift, or equipment degrades.

Digital interoperability should also become a core research objective. Open interfaces, standardized semantic models, robust metadata, and documented data quality would allow building information models, sensors, energy-management systems, maintenance platforms, and lifecycle databases to communicate more effectively. Digital twins should be validated against real operation and accompanied by uncertainty reporting rather than treated as automatically reliable representations.

AI-enabled control and maintenance should also be explainable, secure, and human-centered. Future systems should quantify prediction uncertainty, distinguish correlation from actionable diagnosis, and enable operators to understand why recommendations are generated. Cybersecurity, privacy, computational demand, and model deterioration must be included in assessments of environmental and operational value.

Climate justice and participatory governance require greater attention as well. Vulnerability, access, affordability, and institutional capacity should inform the prioritization of urban adaptation and retrofit investments. Participatory weighting of multicriteria frameworks and co-design with occupants, operators, children, educators, and local communities can improve legitimacy and reveal needs that purely technical indicators overlook.

Finally, more attention should be given to the move from isolated pilot projects toward solutions that can be implemented on a larger scale. This requires economic analysis, practical procurement guidance, workforce development, policy support, and monitoring procedures that others can reproduce. The important question is no longer only whether a solution can work. Rather, it is under which technical, financial, behavioral, and governance conditions it can be maintained and expanded without losing its performance or its social value.

Overall, this Special Issue brings together four complementary contributions to the discussion on sustainable built environments and cities. Climate-resilient schoolyards show how public space can serve simultaneously as climate-adaptation, social, and educational infrastructure. The construction-waste study demonstrates that small but systematic improvements can reduce both costs and embodied carbon. The classroom-lighting paper highlights the need to balance energy efficiency, climate responsiveness, and user experience. Finally, the digital-maintenance study shows how real-time monitoring and predictive approaches can improve the reliability and resource efficiency of renewable-energy assets.

What these papers share is the idea that sustainability depends on integration and continuity. Environmental ambitions need to be translated into measurable decisions, supported by reliable data, adapted to local conditions, informed by users, and followed through maintenance and evaluation. Further progress will require stronger links between lifecycle thinking, climate resilience, circular resource use, intelligent operation, and social equity. We hope that the findings and open questions gathered in this Special Issue will encourage further interdisciplinary work and support the transition toward built environments that are not only lower-carbon, but also more resilient, resource-conscious, inclusive, and able to learn from their own operation over time.