In order to meet the mid-century carbon reduction targets and to mitigate climate change and global warming it is imperative that embodied greenhouse gases (GHGs) emissions in the built environment receive immediate attention from policy, industry and academia. While academic research has grown in recent years, the uptake of embodied carbon assessments in practice has been slower. This paper reports the findings of a collaborative project between industry and academia to shed light on how to accelerate a wider uptake of embodied carbon assessments in buildings. Five projects have been each examined by three assessors (independent environmental consultants) for a total of fifteen detailed assessments. Results are presented for each of the five case studies, showing elements of agreement and, most often, of variation. Additionally, each of the life cycle stages as defined by the TC350 standards is analysed both numerically and in terms of its contribution towards the whole life embodied carbon. The results show that significant discrepancies consistently exist even when the initial information available to the assessors is the same. The numerical analysis also reveals that all life cycle stages account for important shares of the whole life carbon, and that therefore partial assessments – e.g. cradle-to-gate - are not sufficient if carbon reductions are to be realistically achieved. Future research in the field should continue to address the challenges identified in this article and work towards greater understanding and reliability of the numbers produced.