# Implementing Circular Economy Strategies in Buildings--From Theory to Practice
## 3 CE Background and Principles in the Built Environment  
The need for better management of resources that are becoming scarcer, and dire environmental impacts has urged academia and policymakers to provide a new pattern to move away from the economic model adopted since the industrial revolution. The idea of CE was refined throughout the last century to be widely acknowledged during the previous decade. Nevertheless, the roots of CE are still ambiguous and cannot precisely be pinned to a single research. One common agreement is that CE is deeply rooted in numerous schools of thought. [PERSON], an architect and industrial analyst, together with [PERSON], released the research report named _\"The potential for substituting Manpower for Energy,\"_ which focuses on an economy in loops and its outcomes on job creation, economic competitiveness, resource savings, and waste prevention [23]. [PERSON] also worked on a new approach to production and processes, the \"closed-loop\". It aims at promoting product-life extension, long-life goods, reconditioning activities, and waste prevention. His latest work focuses on \"Performance economy\" [24] where he claims the importance of selling services instead of products, which is considered a key feature of CE. The Cradle-to-Cradle concept was developed by the German chemist and visionary [PERSON] and the American architect [PERSON] [25]. The Cradle-to-Cradle concept considers all materials involved in industrial processes as nutrients from two categories: technical and biological. This framework deals with the design for effectiveness and positive impacts while reducing negative ones resulting from design for efficiency [26]. The industrial ecology focuses on material and energy flows through the industrial systems [27]. The concept arose as a solution to resource scarcity and high material cost. This approach intends to create closed-loop strategies that promote waste as an input to eliminate the notion of undesirable by-products while promoting regenerative use of resources [28]. Consequently, wastes and resources stream in a circular way between the different ecosystem components with renewable energy supplying those cycles [29]. Back in the 1970s, the American professor, [PERSON], challenged his students to come up with an idea for society by adopting the following approach: \"daily actives are based on the value of living within the limits of available renewable resources without environment degradation\" [30]. The idea of regenerative design relies on developing buildings and cities to regenerate ecosystems [31]. This concept has been formulated earlier for agriculture and has its roots in bioregionalism and permaculture, but [PERSON] expanded it to the entire social-ecological system to broaden its ability to enhance its potential [32]. Among the front-runners in terms of CE implementation, the Chinese government started to show an increasing interest in the concept by implementing explicit policies back in 2002. Later on, research on CE increased exponentially through the CE promotion law in 2009, to stimulate cleaner production, develop eco-industrial parks, and cope with the rapid urbanization [33; 34]. In Europe, the Ellen MacArthur Foundation's creation and the release of the action plan by the European Commission accelerated the transition towards the CE by promoting renewable energy, designing out waste and closed-loop systems to retain material's value circulating in the economy. Initially, the CE-related Chinese literature framed the concept around the 3R's principles, Reduce, Reuse, and, Recycle [35; 36; 37]. Wherein, \"Reduce\" refers to the action of minimizing inputs and outputs such as raw materials and waste, \"Reuse\" is the operation of using a product again for the same purpose when it reaches its end-of-life, and \"Recycle\" is the process of recovering waste to manufacture a new product. The 3R's principles were later extended to a 9R's framework to encompass more actions and achieve a transition towards CE more effectively.