Informing architectural design processes in a circular economy - the quantification of circular construction

Research output: Book/ReportPh.D. thesis

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Abstract

The construction sector contains great potentials to contribute to our society's green and circular transition since the construction sector is responsible for the emission of 40% of all greenhouse gases and produces 40% of the waste generation. Several political initiatives have been adopted in recent years to accelerate a sustainable transition of the construction sector, such as the European Green Deal from 2020 and the introduction of Danish requirements for CO2 limits and mandatory LCA calculations for new construction from 2023. However, the transition occurs very slow and large scale applied circular and sustainable principles are still only represented in very few buildings. Therefore, there is a need to generate more knowledge and awareness about the potentials for implementing circular economy in both new construction and in the existing building stock. Through case studies, data mappings, analyses, and collaborations with industry and public administration, this project has investigated the circular potential in the existing building stock by focusing on demolitions, lifespans, and circular design strategies.

Through data mapping, several Danish registers for building data were identified. The data mapping showed that there is generally little knowledge about the material composition of the existing building stock. The material composition of Danish building typologies was investigated by collecting pre-demolition audits submitted to the municipality, which were analysed via material flow analysis. However, it turned out that the data quality of the pre-demolition audits was too low to determine the material composition, so it was impossible to make accurate material estimates for similar building typologies based on the current data. Thus, an alternative parametric model was tested based on data from historical typology studies of the most commonly used building parts in existing buildings. A comparison showed that the parametric model could provide more accurate material estimates if extensive typology studies were available. In addition, the parametric model could also generate a 3D model that can be used for verification, visualization, and future analyses on existing buildings.

Demolition data was obtained on more than 120,000 demolition cases over ten years from one of the identified registers in the data mapping. An analysis of the demolition data was carried out in order to examine demolition patterns and the lifespan of existing buildings. These analyses showed that mainly industrial buildings are demolished and replaced with housing. A study of the lifespans of newer industrial buildings also showed that newer office buildings will have a shorter expected lifespan than older office buildings. This was a general trend for most building types, where the expected average lifespan is longer for old buildings than for new buildings. In addition, a comparison of demolition patterns in Denmark and the Copenhagen region showed that newer buildings in Copenhagen were demolished more often than in rest of Denmark where older buildings are most often demolished.

A comparison of new construction and demolition showed that 5-6 times more square meters are built than are demolished, which significant limits how much circular materials from demolitions can replace in new construction. There is, therefore, also a great need to focus on flexible waste prevention strategies such as refurbishment and transformations that can reduce the need for new construction.

Although circular materials can only cover a small part of our need for new materials, there are significant environmental and climate benefits from circular reuse, which was demonstrated in this project through a comparative LCA study of selective demolition with subsequent preparation for the reuse of steel facade panels as was compared to conventional demolition with subsequent recycling of the steel. Here the result showed that across all environmental categories, there was a saving by reusing rather than recycling and that the reuse scenario resulted in a CO2 saving of around 40%. Still, there is generally a lack of much more evidence in order to confirm whether this applies to all materials and what significance the use of circular materials and components in new buildings will have on the overall environmental impact.
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages152
Publication statusPublished - 2023

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