Environmental Benefits of Reusable Modular Mass Timber Construction for Residential use in Japan: an LCA Approach

Abstract

The demand for wooden buildings in Japan consistently reaches figures over 50 million square meters per year. However, the building industry in Japan is based on the constant renewal of the building stock, leading to a short average lifespan, and an unsustainable and wasteful system both from the environmental and economic point of view. As an alternative to this situation, this study assesses the environmental benefits of a modular mass timber system using CLT, designed for consecutive reuse. First, the study presents an award-winning proposal for a modular, reusable mass timber system for residential construction in Japan. After, the study calculates the Global Warming Potential of construction (GWP) of the reusable system in comparison to a conventional mass timber system (benchmark), using the Lifecycle Assessment (LCA) method. The study evaluates the proposed system in two different locations, within 60 years. Three different scenarios for forest resources are considered during the above time-frame, namely stable forest (standard), growing forest (optimistic) and decreasing forest resources (pessimist) to understand how changes in the carbon flow of forests could impact the environmental output of the construction. The results show a modular construction system can be used to provide high-quality dwellings in Japan leading to a significant potential for mitigating the impacts of construction on the environment. More specifically, a growing forest scenario provides the smallest GWP, more than 100% smaller than the benchmark.