A Life Cycle Assessment of Medium Density Houses in New Zealand

This study develops an analysis method that designers can use to undertake a Life Cycle Assessment (LCA) on multiple building designs to inform design decisions and trials this on Medium Density Housing (MDH).  Measuring the environmental impact of a building is a time and resource-intensive process requiring multiple analysis tools, numerous inputs and quality assurance steps. Together with a lack of knowledge from designers, this makes it an unattractive task. Therefore, a method was needed to remove these barriers so that an LCA could be integrated into a designer’s workflow to inform design decisions. To simulate issues designers would face in the early design stages when undertaking an LCA, an LCA was performed on three MDH houses using selected designers’ Building Information Modelling (BIM) models in a warm and cool climate (Auckland and Christchurch). The LCA impact of changes to the insulation levels above the New Zealand Building Code minimum was examined to test the utility of the process.  Unique in the literature, this study includes multiple LCA indices: material impacts, resultant operational energy use, change in materials, multiple environmental indicators, the rationale behind the selected buildings, quality assurance of the results, presentation of model inputs and all results in sufficient detail for the methodology to be tested and replicated.  The case study research methodology developed three MDH houses that were representative of a broad range of MDH houses currently for sale in New Zealand. The goal was to evaluate whether the research method can identify differences between buildings that might inform design choices.  In theory, a single BIM model eliminates the need to have three building models: the designer’s construction model; the LCA analysis model; and the energy performance model saving time and complexity for the designer. This methodology identified that it was not possible to have a single BIM model in Revit and use this for both an energy simulation and LCA using LCAQuick. Each house was recreated in OpenStudio for simulation in EnergyPlus to generate the energy performance of each house.  A database of inputs for the energy models was created, which was quality assured for use by designers. A visual assessment diagram was created to allow designers to interpret the output to help inform design decisions.  The case study analysis determined that the design of the houses had a more significant effect on reducing environmental impact compared to increasing insulation levels above the minimum required by the building code. Changes to the buildings’ insulation levels resulted in an average change in environmental impact across the seven environmental indicators ranging from -1 to 7% in Auckland and -2 to 2% in Christchurch, whereas differences in the design resulted in a change in environmental impact of 21 to 22% in Auckland and 22 to 23% in Christchurch.   The research has demonstrated that LCA can be integrated into a designer’s workflow. Designers can assess the environmental impact of multiple houses and construction changes in different climates and with multiple construction changes to each. However, the process requires further refinement. There is still a need to develop the Computer-Aided Design (CAD) modelling methods and their integration with the analytical tools.