Circularity of building stocks: modelling building joints and their disassembly in a 3D city model

Improving circularity in the building sector entails ensuring greater material efficiency to avoid virgin material extraction. This effort could reduce net negative environmental impacts related to building materials. The circular use of building elements requires to assess which elements from the building stock can be salvaged for re-use, repair, etc. Hereto, products and materials are to be inventoried, and info about their assembly is crucial to assess their disassembly potential. Assembly refers to the relative geometric positioning of building elements and their connections. Assemblies, such as building joints, determine the actions and costs necessary to salvage products in a damaged or undamaged state from a building. Depending on this state, the products can be re-used or recycled. In other words, to understand and alter salvaged material flows, adequate ways to model building joints and disassembly are needed. Additionally, an approach to store data on these building joints on the scale of clusters of buildings and cities should be developed. This would enable to gain insight in the salvage potential of building products for any size of building stock, and to determine the stock’s circularity potentials. To this end, the study consists of four steps. (i) Properties of building components that affect disassembly are discussed, including their storage in material passports. (ii) Methods to model the disassembly sequence of building components are reviewed and fit disassembly modelling methods are selected. (iii) These methods set the data necessary on building joints, which can be subdivided in geometry, connection means and dependencies. (iv) A proposal is made to store building joint data in a 3D city model, such as a 3D GIS model. In this workflow, a novel database is proposed that relates data on building joints and building elements to unique codes. In the 3D city model, codes of building elements can be attached to digital surfaces, and codes of building joints to edges of surfaces. Aside from storing building joint data in 3D GIS, we discuss applying this in BIM. To conclude, this study presents a novel workflow to model building joints and their disassembly, which enables the modelling of building product salvaging for any size of building stock.