Social housing providers have recently emerged as unlikely innovators of low carbon transitions in the UK residential sector. They tend to have a significant amount of influence over large housing stocks, opportunities to access funding to retrofit on a large scale, can make explicit connections between reduced carbon emissions and improved quality of life for low-income residents, and foster a close relationship with the place and communities they serve. In effect, social housing providers are 'middle actors' who not only facilitate but also realise low carbon transitions through various strategies. This paper uses empirical findings from interviews with social housing providers in Greater Manchester to understand the different ways that low carbon and energy efficiency innovation is being undertaken in this sector. The findings reveal that as middle actors, social landlords influence upstream to policy makers and regulators, downstream to individual households, and sideways to other actors in the social housing sector as well as to other building and energy professionals. The findings reveal opportunities for governments to supplement their existing policies with recognising and supporting middle actors to accelerate low carbon transitions of the built environment. (C) 2018 Elsevier B.V. All rights reserved.