The traditional model of taking single actions when components reach their end of life or provide inadequate service has enabled the residential sector to gradually improve its energy efficiency over time. However, to achieve the large potential reductions in energy consumption and greenhouse gas emissions in residential buildings, a deeper systematic approach is required. The house as a system approach to energy retrofits emphasizes that for the greatest improvements in energy performance, multiple retrofit actions must be taken, and the order is important. This was the core concept in the Canadian residential energy efficiency programs, EnerGuide for Houses (1998-2006) and ecoEnergy (2007-2012). In this study, a systematic analysis of a large dataset that documents 19,552 residential energy evaluations conducted by a single agency in Waterloo, Canada, allows for a more nuanced description of how well the energy retrofit actions taken by participants followed the house as a system approach. The findings are encouraging in that participants did respond to the multiple recommendations given to them by energy advisors. In particular, a higher number of recommendations were associated with households arranging follow-up evaluations and taking more action under the performance-based grant program. However, the results also illustrate that participants frequently did not attend to the retrofits in the combinations associated with the house as a system approach. Insulation to reduce heat losses should have been the first priority in the systemic approach, but was often not upgraded, and the extent or depth of the upgrade was often less than what had been recommended. Furnaces and windows, which should have been upgraded in combination with or after the building envelope, were often upgraded as singular actions, demonstrating the persistence of the traditional model in some households. Time-limited grants do not appear compatible with encouraging the house as a system approach; it appears that staged approaches and careful attention to the building envelope retrofits would allow these programs to promote the house as a system approach to encourage deep retrofits and achieve low-carbon housing.
