A comparative life cycle assessment of offsite and onsite construction methods

Abstract

This research aimed to determine whether offsite construction leads to a lower environmental impact than onsite construction. Further, it is researched how the environmental impact of offsite construction can be reduced. This is of great importance as the construction industry has a significant environmental impact. Specifically, offsite construction is extra relevant as the Dutch government chooses to stimulate offsite construction methods for its lower environmental impact.

First, relevant information about offsite construction methods and environmental impact assessments are researched by literature study. The environmental impact of 2D panelized and 3D volumetric construction is likely to differ as the amount of work offsite and transport logistics are different. Then, the MPG is selected as the method to assess the environmental impact. This tool measures the environmental impact of building materials throughout their lifetime. An MPG calculation is needed to obtain a building permit for residential buildings.

Next, the differences between the following construction methods are compared and studied: onsite construction, modular offsite construction and panelized offsite construction. This is done through case studies of each of these construction methods.

The cases were compared on their differences in construction methods with a focus on differences in materials and processes.

The cases were then compared on their environmental impact through the MPG calculations. The scope of the MPG was limited. Services and space plan (like kitchens and toilets) as described by Brand (1994) were left out of the assessment. Interior walls and doors however, were part of the assessment. The calculation showed that the environmental impact or the MPG was highest for the onsite case and lowest for the modular case. Offsite construction did come with a lower environmental impact than traditional construction in this study.

Four strategies were identified after looking into the MPG comparison done in this research and in two other comparisons done by other researchers to lower the MPG.
To bring down the environmental impact:
1. Limiting the use of materials
2. Choosing different materials

To bring down the MPG score:
3. Use more cat 1 or 2 data
4. Enter a longer lifespan for a building

Subsequently, these 4 strategies are tested on their viability and effectiveness in the case of Leerpark Dordrecht.
Strategy 1 was not feasible in this specific case, the other 3 strategies proved viable and effective. These strategies would lead to a 29% reduction in the MPG compared to the MPG made earlier in this research.
However, there are limitations to the MPG when comparing the environmental impact of different buildings:

• The material-based approach does not allow to account for the design as a whole.
• The NMD is lacking data. There are not enough cat 1 or 2 items available in the NMD.
• The energy performance of buildings is often enhanced by using building elements that negatively impact the MPG, like solar panels or insulation panels.
• The MPG does not help lower construction emissions now as the embodied energy is spread over 75 years.
• Biobased materials are not fairly assessed in the current system.