Increasing the energy efficiency of the existing housing stock is widely recognized as an important approach to reducing greenhouse gas emissions and increasing sustainability. However, energy systems are complex, and involve a variety of ever-changing technologies, systems of provision, infrastructures, energy users and resources. This project uses social practice theory to identify the sociological barriers and opportunities to enabling residential energy efficiency in Guelph, Ontario. To achieve this goal, semi-structured interviews and surveys are used. The primary barriers and opportunities related to the facets of meanings, materials, and competences are identified, and recommendations for overcoming the key barriers are outlined. Moving towards a more sustainable future requires rethinking the use of traditional methods of analysis for studying residential energy efficiency, and substituting less effective units of analysis for more powerful ones; particularly social practices.