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Buildings are big consumers of energy and materials, and important producers of waste and emissions. Prefabrication presents an opportunity to reduce impacts in the building sector; however, few studies have focused on prefabricated houses and with contradictory findings. The main goal of this article is to assess the embodied energy (EE) and greenhouse gas emissions (GHG) of a prefabricated modular house, based on a modular system to enable different layouts. A "cradle-to-site" analysis was performed, including materials production, transport to plant, modules' production, transport to site and final assemblage on site. Several house final locations were addressed to assess transport related impacts. Scenarios for alternative building structural materials (steel; concrete; timber and light steel framing (LSF)) and house size (bedroom number) were also analyzed, aiming at understanding the influence of these aspects in the results, and representing other prefabricated modular houses currently produced in Europe. The calculated embodied impacts show that materials production is the most important phase (64-90% of EE and 59-87% of GHG) and that the structures with LSF framing or timber have the lowest impacts, while steel and concrete the highest. Embodied impacts increase with the house size; however, a larger house leads to lower impacts per inhabitant, but similar impacts per m(2) (similar conclusion could be drawn for non-prefab buildings). The impacts of transportation (of modules, workers and finishing materials) vary significantly for the various house final locations and can be significant for overseas locations, which can jeopardize the potential benefits of modular prefabrication. (C) 2018 Elsevier Ltd. All rights reserved.