Comparative study of greenhouse gas emissions between off-site prefabrication and conventional construction methods: Two case studies of residential projects

Abstract

Greenhouse gas (GHG) emissions in the construction stage will be more relatively significant over time.Different construction methods influence GHG emissions in the construction phase. This study investigates the differences of GHG emissions between prefabrication and conventional construction methods. This study sets a calculation boundary and five emission sources for the semi-prefabricated construction process: embodied emissions of building materials, transportation of building materials, transportation of construction waste and soil, transportation of prefabricated components, operation of equipment, and construction techniques. A quantitative model is then established using a process-based method. A semi-prefabrication project and a conventional construction project in China are employed for preliminary examination of the differences in GHG emissions. Results show that the semi-prefabrication method produces less GHG emissions per square meter compared with the conventional construction, with the former producing 336 kg/m 2 and the latter generating 368 kg/m 2 . The largest proportion of total GHG emissions comes from the embodied emissions of building materials, accounting for approximately 85%. Four elements that positively contribute to reduced emissions are the embodied GHG emissions of building materials, transportation of building materials, resource consumption of equipment and techniques, and transportation of waste and soil, accounting for 86.5%, 18.3%, 10.3%, and 0.2%, respectively, of reduced emissions; one a negative effect on reduced emissions is the transportation of prefabricated components, which offsets 15.3% of the total emissions reduction. Thus, adopting prefabricated construction methods contribute to significant environmental benefits on GHG emissions in this initial study.

Estimation and Minimization of Embodied Carbon of Buildings: A Review

“…LCA provides a holistic approach for quantifying the environmental impacts, including associated emissions and energy use, of the buildings. The common LCA approaches may be categorized into statistical analysis, process based analysis, economic input-output analysis and hybrid analysis methods [97,118]. While providing a detailed and reliable assessment, the statistical-analysis-based LCA is generally difficult to perform due to its high reliance on availability of comprehensive statistics, and thus has had limited use in previous studies [118].…”

“…While providing a detailed and reliable assessment, the statistical-analysis-based LCA is generally difficult to perform due to its high reliance on availability of comprehensive statistics, and thus has had limited use in previous studies [118]. The process-based analysis, on the other hand, is a commonly used bottom-up method, which involves identifying all materials and energy flows associated with different activities involved in the production of a material or provision of a service and quantifying the corresponding environmental impacts [113,118]. The results of process-based LCA are detailed and process-specific and thus may be used to compare specific products and processes or identify areas for process improvement.…”

“…Examples of such efforts include studies conducted by Hammond and Jones [24,25] as a part of the Carbon Vision Buildings Program at the University of Bath, England, which led to the development of a comprehensive inventory of the embodied carbon of building materials, which has since been used in several studies. Similarly, the studies conducted by the Centre for Building Performance Research in New Zealand [118,124] led to the development of an "Embodied Energy and CO 2 Coefficients for NZ Building Materials" inventory.…”

“…The common LCA approaches may be categorized into statistical analysis, process based analysis, economic input-output analysis and hybrid analysis methods [97,118]. While providing a detailed and reliable assessment, the statistical-analysis-based LCA is generally difficult to perform due to its high reliance on availability of comprehensive statistics, and thus has had limited use in previous studies [118]. The process-based analysis, on the other hand, is a commonly used bottom-up method, which involves identifying all materials and energy flows associated with different activities involved in the production of a material or provision of a service and quantifying the corresponding environmental impacts [113,118].…”

Modular vs Conventional Construction: A Multi-Criteria Framework Approach

“…Some studies suggest the dominance of semiprefabrication methods over conventional construction approaches in terms of minimising construction related embodied carbon [6], and greenhouse gas emissions [7]. Though there are studies that have also attempted to contrast separately the economic [8] or environmental impacts [6], [9] of construction methods, no attempt has however been made to contrast volumetric construction methods such as modular with conventional methods using an encompassing approach.…”