Material efficiency in architectural glass and façade design: Steps toward reuse

Abstract

Reuse and high-value recycling have a pivotal role to play in reducing waste and minimising the ecological impact of activities in the built environment. The optimisation of building energy performance in use has received significant attention to date. This, together with the aim to advance other performance criteria such as occupant safety and user comfort, has stimulated the evolution of façade systems that serve numerous functions. Increased functionality has been achieved through the use of a broader range of material resources, advanced processing methods, and more complex construction techniques which paradoxically may reduce the ability to recover material resources at the end of their design life. To date, very little attention has been paid to the consequences of incorporating multiple layers of components and greater proportions of irreversible connections on the ease of disassembly and reuse. Future targets for reducing whole-life carbon emissions will not be met without an improved understanding of how to recover components from new and existing façade systems effectively. This research thus examines the role of material efficiency in façade design, with a focus on reuse and high-value recycling, across the façade life-cycle. The behavioural, environmental, and technical factors affecting design strategies for reuse and recycling are investigated. Through engagements with 69 stakeholders across the value-chain, this research first investigated the challenges and opportunities associated with façade reuse as perceived by those in the façade sector. A mixed-method approach of data collection was employed in which the responses from a preliminary set of surveys were examined in more detail through semi-structured interviews. Through this, it was found that the adoption of design strategies that facilitate reuse and recycling is dependent on: increased awareness and quantification of the environmental value of material resources beyond their first use; new business models; cross-supply-chain support for accompanying take-back infrastructure; and advancements in efficient practical separation methods specific to façade components. Enhanced communication between stakeholders addressing acceptability criteria and product availability; new reconditioning methods; and more holistic legislation based on whole life-cycle performance also emerged as vital requisites for advancing material efficiency. Subsequently, the convergence and divergence in stakeholder priorities related to these factors was examined. Glass is a key construction material in the materials palette for contemporary façade systems. A material flow analysis of the UK flat glass sector was constructed in this research. This revealed that the practical reuse of architectural glass rarely takes place and closed-loop recycling rates are low, despite the potential for significant energy and carbon dioxide (CO2) savings. Opportunities to improve recycling rates were identified in: new producer responsibility schemes; capital investment in collection infrastructure; cullet quality monitoring; demonstration of the financial costs / benefits associated with consideration of the CO2 emission reduction from increased cullet use; and the establishment of supporting policies. Each of these options would require further research and support to be fully realised. Many contemporary façade systems consist of multi-material composite components which are difficult to disassemble and reuse or recycle at their end-of-life. A literature review of existing environmental assessments revealed the need for a bespoke methodology that accounts for these design complexities. The new assessment method developed in this research enables a quantitative evaluation of the environmental reclamation potential over time. The reclamation potential measures the influence of material selection and construction methods on the ability to disassemble and reuse recovered façade products at their end-of-life. The method accounts for the technical service lifetimes of components, including performance degradation over time, and can thus inform suggestions for the most suitable recovery route (system reuse, component reuse or recycling). The newly developed method was applied to four glazed façade typologies. Results highlight that the use of permanent adhesive connections can significantly limit the environmental value of connected components at their respective end-of-life, due to service life dependencies on neighbouring components. In addition, it was shown that the additional life-cycle environmental impact associated with recurring resource inputs for component replacements requires greater attention in order to avoid promoting designs that shift the environmental burden to other life-cycle stages. The existing technological barriers affecting the disassembly of contemporary façade systems for component reuse were reviewed. The parameters affecting the end-of-life separation of laminated glass - a composite of glass and poly-vinyl butyral frequently used in façade glazing - were examined through a series of experimental investigations. The interfacial strength between glass and poly-vinyl butyral was found to be significantly affected by moisture, temperature and glass surface properties. At a small scale (12500 mm2), under specific conditions, delamination phenomena between glass and PVB was observed. This is a key area for future research into developing efficient separation processes for façade components with the long-term goal of preserving material value in the built environment. The realisation of resource-efficient façade designs requires a systematic review of behavioural, environmental, technological, legislative, economic and social factors. This research investigates the first three of these and thus (i) presents an informed overview of the key challenges and opportunities in façade reuse as perceived by the façade value-chain; (ii) develops a new framework for assessing the environmental reclamation potential of complex designs; and (iii) investigates new methods for alleviating technical barriers in reuse, to open up opportunities for reducing the environmental impact of future construction. Future research directions are identified which could build upon the outputs of this research and thus promote the practical realisation of material efficiency in façade design.