The UK's housing stock generates approximately 27% of the country's total annual carbon emissions. In light of the legally binding targets to reduce carbon emissions, new housing is subject to a tightening of regulations governing energy demand and efficiency resulting in a gradual improvement in carbon emissions. The question is how to achieve the deep carbon emission reductions from existing domestic properties, of which 75% will still be in use in 2050. Government has sought to provide incentives to homeowners to improve the energy efficiency of their households, and mandate improvements in socially rented housing using a range of fiscal measures, most recently the ‘Green Deal’. There has however been little consideration of the 18% of UK households who privately rent their home, a tenure that is growing fast. The aim of this research is to investigate the factors that influence private sector landlords when considering energy efficiency improvements to their tenanted homes. The results indicate that government policy has consistently failed to engage private sector landlords in the issue of energy efficiency and thus measures must be taken to understand the motivations of landlords in order to design effective incentives and interventions.