Internal wall insulation as a retrofit measure could help to reduce energy use and greenhouse gas emissions in many of the 6 million solid wall buildings in the UK. However during retrofit, junctions that are hard to deal with are often left uninsulated, increasing heat loss and surface mould growth risk at thermal bridges. Furthermore the effect of junctions, insulated or uninsulated is not properly taken into account in commonly used assessments of heat loss. This paper presents a study on the impact of the junctions around openings, also called reveals, on the transmission heat transfer coefficient of internally insulated dwellings and a discussion on potential areas of improvement of common assessment tools for retrofit. Findings showed that reveals account for the majority of the transmission heat transfer coefficient at junctions, that thicker wall insulation is not necessarily advantageous from a heat loss perspective, and that the transmission heat transfer coefficient at junctions per unit area of exposed elements was often higher than the reference value used in the UK. (C) 2016 The Authors. Published by Elsevier B.V.