Embodied transport energy of a prefabricated timber wall panelling unit

Increased demand for more affordable homes in recent years has led to recent resurgences in the use of prefabricated construction method. Although there have been various environmental advantages associated with prefabricated construction techniques, the judgement against it is believed to be based on limited understanding and without the necessary detailed research on its environmental performance. The main environmental issues associated with prefabricated houses lies in its transportation pattern and the effect it has to the overall embodied transport energy. The complexity and dynamics of transportation processes, e.g. from forest to site in the case of building prefabricated timber houses, reveals the importance in having a better understanding of the significance of embodied transport energy consumption associated with prefabricated construction. Due to high dependency on imported timber, concern has been raised over transport energy consumption when using prefabricated timber elements on UK construction sites in contrast to masonry materials that are readily available locally. This research therefore analyses the embodied transport energy consumption when using prefabricated timber elements for building affordable homes in the UK with particular reference to the use of prefabricated timber wall panelling unit. The evaluation of embodied transport energy has been carried out through the use of process flow analysis. This research has developed a generic process flow model for using prefabricated timber wall system in the UK. Primary data has been gathered through questionnaires to identify the most commonly used prefabricated timber panelling system, its components, the origins of raw material along with the transportation and material processes involved for each component. The questionnaires revealed that open wall panelling system is the most marketed prefabricated timber wall type in the UK. Based on the findings of the questionnaires and the developed process flow model, a number of mathematical formulae have been developed in order to systematically quantify the intricate embodied transport energy consumption associated with using prefabricated timber wall panelling unit on construction sites. Scenario analysis has been employed in order to test the functionality of the system methodology and to demonstrate the way embodied transport energy may vary within a set of variables. The results suggest that the unit difference between the embodied transport energy of a scenario when delivering a single wall panelling unit to site compared to having vehicles fully loaded with panelling units is as much as 16.83GJ/panel. The process flow analysis concludes that it is environmentally friendly to employ prefabricated timber frame construction for large housing development projects such that delivery to site is always with a full load. Another important finding is that waste factor of building materials has a significant effect on the overall embodied transport energy consumption especially the waste factor of converting the logs onto plywood and studs used to produce the prefabricated timber wall panelling unit . The research has provided a better understanding of the effect of transport load, choice of transport, and the transportation distances on the overall embodied transport energy for prefabricated building elements and their associated materials. It can be concluded that the developed process flow analysis model has potential to be used as a base model to analyse other type of materials used within prefabricated house construction to aid decision making.