# Implementing Circular Economy Strategies in Buildings--From Theory to Practice
## 4 CE Strategies for Energy, Materials, and Water  
Natural resources are substantially used and consumed throughout the buildings' life stages as this industry is responsible for around 30% of water use and 40% of raw materials extraction and energy consumption [2; 43; 44]. By adopting particular CE strategies, savings may occur by creating proper systems to retain value and keep the resources flowing in a circular manner [45]. This approach would close materials and components, energy, and water loops and minimize the associated potential environmental impacts [46]. The life cycle of circular buildings should be a closed-loop system wherein components and materials are optimally used and retained at their highest value (Figure 1). The technical cycle consists of selecting materials and components that can be maintained to extend their service-life by reusing, refurbishing, repairing, and remanufacturing [21]. At the same time, recycling and incineration are final strategies. While, on the other hand, the biological cycle involves natural materials that can be biodegradable or compostable at their end of life (e.g., bio-based materials) [47]. According to [PERSON] and [PERSON] [42] circular buildings encompass green and sustainability strategies. The environmental footprint of materials and components should be as minimal as possible. It is preferable to select locally sourced materials to reduce emissions due to transportation and stimulate the local economy. Low embodied energy and carbon materials that are abundant, renewable, and pure are fundamental strategiesto achieve eco-friendly structures with a minimal input of raw materials within a circular flow system. Circular building design entails adaptability, flexibility, and deconstruction at its core. Materials and components need to endure numerous life cycles, depending on the use purpose. Therefore, durability and resilience are two features that need to be taken into account when selecting materials and components to ensure no loss in quality or value over time and use-cycles. Throughout the building's lifecycle, energy is substantially used and consumed, from materials extraction and processing to the building's construction, operation, and demolition/deconstruction phases [48]. Recent policies regarding Nearly Zero-Energy Buildings (NZEB) challenge practitioners to produce buildings with high energy efficiency [49]. In this context, circular buildings can achieve energy neutrality and even produce an excess of energy through design and on-site renewable energy production [50; 51]. The overall energy consumption of buildings is mainly allocated to building operations, followed by embodied energy [52]. The use of materials and components that are energy-intensive increases the buildings embodied energy and, therefore, the life cycle energy consumption. In Europe, energy consumption related to building products ranges from 5% to 10% [53]. Another critical parameter to reduce energy consumption during the use phase is enhancing the building's thermal insulation. High-quality materials are needed to provide the necessary services and thermal comfort for the users [54]. Hence, materials selection and  
Figure 1: Closing materials and components loops in buildings. contextual building design and layout should be considered to reduce energy consumption throughout the building's life-cycle. With the global urbanization, water is getting scarcer since this resource is encountering an increasing demand, and many researchers have predicted a freshwater crisis by the end of this century [55]. In all buildings' life cycle, water is considerably used and consumed by all building stakeholders. Similarly to energy consumption, water is most consumed during the operation phase by building users, followed by buildings' embodied water [56]. Water is used to manufacture several building materials, such as concrete and cement-based materials, ceramics, coatings, and steel. Selecting low embodied water materials will eventually decrease the building's water footprint.