# Adaptability of Buildings: A Critical Review on the Concept Evolution
## Content Analysis
### Enablers and Promoting Models
#### 3.3.3 The Circular Economy in Buildings
In this respect, prefabricated modular units create an important example providing further value for reduction, reusability, adaptability, and recyclability of their components [94]. Standardization can be achieved at three levels: material, component, and connection. However, each level has a distinct advantage. For example, standardized materials allow for more efficient recycling while standardized components create specific conditions for connections [57]. Connectionsin this context grasp major attention due to their importance as vital elements [50,64] in facilitating the change by enhancing the efficiency of modularity through ensuring easy removal and replacement of standardized components [2]. Standardization of connections could be of great value as it exempts the components from being standardized [57]. The use of standardized grids and modularization also facilitates component interchangeability, which is seen as a great enabler of adaptability [7], particularly in commercial office buildings where adaptability is a main stream [4]. * **Material passports for facilitated reuse. ** Choosing adequate materials can have a potential influence on adaptability values [2,74]. They are also seen as an important pillar to achieve circularity in building design. [PERSON] [57] found that circularity values (thus adaptability values as well) come up when specified intrinsic properties (material and product characteristics) cross with relational properties (building design and use characteristics). What were found to be the right options in the process of materials selection are new or reused biobased or technical materials that can be reused to their highest degree, or a hybrid solution of those two [89]. Those also have to be of high functional quality and of sustainable nontoxic origin [57]. Buildings containing hazardous materials (e.g., asbestos) have less potential for adaptive reuse due to the high risk and elevated costs associated with extraction or containment [2]. Conversely, durable nontoxic materials are important enablers for adaptive reuse projects where they contribute to a prolonged functional life of a building and reuse of its components in other projects [2]. Given all that, new materials must be developed to allow further opportunities for reuse and adaptations of buildings [80]. The use of secondary materials is an important enabler for the waste hierarchy (Reduce, Reuse, Recycle). Yet, the lack of market mechanisms to support recovery is a critical challenge raised by different stakeholders [95]. In addition, concerns about quality of secondary materials and their adequacy for reuse are perceived as additional challenges in this regard, especially when those are salvaged from old buildings. As for the connections, the use of mechanical connections rather than chemical ones helps to ensure a proper level of independence between functions of building layers and components [49]. When talking about materials' circularity, it is important to mention the concept of Material Passports (MP) brought by the concept of Cradle-to-Cradle (C2C). MP is another concept integrated in the frame of Circular Building (CB) research that relies on producing a document reporting all materials and components composing a building [89]. This document describes all characteristics including composition, value for recovery and recycling, reuse potential, and end-of-life (Eol) financial value.