Addressing housing-related energy consumption and emissions is a challenge in many countries. Low-energy housing, e.g. whole house retrofits and zero-energy new houses, is still rare in the United Kingdom, yet very much required to reduce emissions. This paper contributes to research on low-energy housing by adding new empirical material through analysing how specific drivers linked to knowledge, public policy and intermediary actors can influence successful projects. Based on in-depth case study research of both existing and new built low-energy housing projects in Brighton, United Kingdom (UK), we show that in addition to motivations to improve existing housing conditions, knowledge and available skills of householders and project participants, and both local and national policies, drive such projects. We also find that intermediaries inspire projects, connect different actors and facilitate learning between projects. Intermediaries are important for advancing projects through local actors and knowledge-networks, especially at a time when national policy support for low-energy housing remains limited and a wider transition to low-energy housing is not complete.