A comparative cradle-to-grave life cycle approach for addressing construction design choices: An applicative case study for a residential tower in Aalborg, Denmark

Energy demand reduction targets and sustainable design paradigms are fueling the search for more and more effective design solutions in the building sector, and new technologies and construction systems are being presented. However, each design solution has its own consequences for the environmental impact of the building. The use of Building Information Modelling (BIM) and Life Cycle Assessment (LCA) can be profitably adopted for supporting the decision-making process. This paper reports a comparative methodology developed to analyse the impacts of alternative structural solutions for timber-based high-rise structures. Embodied, operational, and end-of-life environmental impacts based on two structural frame types, a reinforced concrete (RC) structure and cross-laminated timber (CLT) are explored. Two main inputs are used for performing a comprehensive cradle-to-grave LCA for the whole building: the bill of quantities from a Revit BIM model and the energy demand from DesignStudio. Then, an LCA is performed using the One Click LCA tool for a service life of 50 years and 12 impact categories. The environmental impacts of building materials are based on Environmental Product Declarations (EPDs) directly embedded in the tool. The method is then applied to a case study in Aalborg, Denmark. Results indicate that the total emissions for the considered case study are 9.6 kg- CO2 eq./m2/y for the CLT structure against 10.8 kg- CO2 eq./m2/y for the RC structure. The production stage of building materials, including building systems and installations, accounts for around 55% of the total emissions, while energy use (B6 phase) during the in-use stage of the building recorded a lower environmental impact (45%). The outcomes confirm that the opportunity to base the discussion on alternative design options on more objective and data-based elements to support the different positions which already involve a wide range of architectural, functional and financial criteria. This is of great relevance in achieving balanced and informed decisions which do not simply follow green-labelled ideas but are grounded on evidence-based considerations.