The importance of circularity

Urban building demolition generates billions of tons of heterogeneous waste, ranging from concrete debris and structural components to fixtures such as sinks, windows, and various equipment. Beyond contributing to long-term solid waste accumulation, these activities also release pollutants into the air, water, and soil, posing significant risks to human health and ecological systems.

Extensive research indicates that a great part of those materials could be reused or recycled, thereby extending their lifecycle within the construction sector. This is particularly relevant when considering that the construction industry is also one of the prime consumers of resources. Hence, promoting a circular economy in building practices could transform the prevailing linear urban development model into a more sustainable urban metabolism.

Nonetheless, the reuse and recycling of construction materials often face significant barriers in the absence of supportive policies or incentives from public authorities. For this purpose, the Circular Urban Planning tool aims to assist stakeholders in identifying priority materials and supply chains for development and estimate the potential environmental gains from those strategies.

Developing circularity

While most construction materials can be recycled or reused, practical implementation is often limited due to regulatory constraints and underdeveloped supply chains. For instance, in order to reuse a timber beam, its condition needs to be assessed, eventually by conducting mechanical tests. In the absence of standardized methodologies and efficient logistical frameworks, those assessments can be costly and time consuming.

Across all scales of the building sector, stakeholders have a critical role to play. Deconstruction companies can incorporate diagnostic testing to evaluate material viability, architects can design with reclaimed elements in mind, and public authorities along with real estate developers, can mandate the inclusion of reused materials in project specifications.

The Circular Urban Planning tool

The Circular Urban Planning tool aims to support decision-making process towards improving circularity in built environment through implementation of reuse and recycling strategies at urban scales.

The objective of the tool is to identify the most relevant materials and building parts to reuse considering their environmental impact. Using the data provided by the cities the tool evaluates the elements and circular strategies that can be the most beneficial to reuse or recycle from a greenhouse gases (GHG) emissions point of view. In the end, the tool provides information on which supply chains should be developed to prepare the selective deconstruction of buildings as well as their refurbishment.

The Circular Urban Planning is a modelling framework with a bottom-up approach, that integrates material stocks and flows analysis (MFA) over time, into the new parametric model that combines life cycle assessment (LCA) and circularity assessment (CA). The tool is seamlessly integrated as a plugin within QGIS, ensuring straightforward accessibility for urban planners and other stakeholders involved in spatial decision-making.

To apply these methods on a pilot city neighborhood, and perform analyses that yield robust and reliable results, it is critical to rely on national and contextual databases, such as cadastral data, or material composition of typical building types, etc. However, those data can be difficult to access as most cities do not have the detailed plan and material composition of the buildings.

Solving the data gap with computer vision

Image Source: Deepika Raghu, Postdoctoral Researcher at Chair of Circular Engineering for Architecture, ETH Zurich, Switzerland

Addressing data gaps remains a significant challenge, as reliance on assumptions increases the risk of developing inaccurate or ineffective strategies. For this purpose, acquiring precise data on the materials of buildings is essential.

Following this idea, the Chair of circular engineering^(1,2) uses tools built upon computer vision and artificial intelligence to identify building characteristics from photographic sources including publicly available imagery such as Google Street View. These technologies enable the collection of more reliable data, enhancing the accuracy and quality of analysis.

Making circularity the norm

In the face of global challenges such as climate change, resource depletion, biodiversity loss and massive generation of waste, it is imperative to rethink our approaches to urban development. Instead of extracting and damaging the environment, we believe we should work with what is already there. Achieving this transition requires the engagement of all stakeholders in urban planning: from policymakers and architects to developers and deconstruction specialists. Together we can establish circularity as the norm!

Contact

Chair of Circular Engineering for Architecture, ETH Zürich, e-mail: navaro-auburtin@ibi-baug.ethz.ch

(1) Raghu, D. et al. (2022) Enabling Component Reuse From Existing Buildings Through Machine Learning - Using Google Street View to Enhance Building Databases. Available at: https://doi.org/10.52842/conf.caadria.2022.2.577.

(2) Raghu, D., Bucher, M.J.J. and De Wolf, C. (2023) “Towards a ‘resource cadastre’ for a circular economy – urban-scale building material detection using street view imagery and computer vision,” Resources, Conservation and Recycling, 198. Available at: https://doi.org/10.1016/j.resconrec.2023.107140.