The majority of carbon emissions arise from the built environment, a fact which has led to a global policy focus on reducing carbon and energy from buildings in use. However, research demonstrates that embodied carbon is also an increasingly significant proportion of the whole life impacts from buildings. Embodied carbon is not yet the subject of regulation, and although the CEN TC350 standards provide a methodology, there remains a significant variation in its measurement. This paper investigates some of the issues and difficulties that need to be addressed before widescale regulation can be enforced. The investigation uses a detailed case study of a low-energy school building, studied during its construction phase. The cradle-to-grave embodied impacts were modeled to the TC350 Standards using an innovative tool, and the operational impacts were modeled to incorporate future climate predictions. In spite of the care taken over data collection and the collective support of the process from all stakeholders, the study demonstrates a high level of uncertainty in results, resulting from industry-wide barriers to embodied carbon measurement. Key recommendations are made for industry and policy, in order to overcome the current barriers and enable more accurate and comparable measurement of the embodied carbon of buildings.