It is estimated that a third of the 21.7m domestic UK houses are classified as hard to treat (HTT) and these account for a significant portion of the country’s total energy consumption. The Holistic Energy Efficient Retrofit of Buildings project (HERB), is funding a European Union based consortium of seventeen members across the continent. These consist of both industrial and academic partners, with the project aim being the development of a range of renewable / energy efficient technologies and testing through the retrofit of twelve properties in different countries. A series of energy models were carried out for the six UK based domestic houses to be retrofitted in the HERB project. The technologies utilised in this exercise were based on a description specification in the Project’s outline. An economic tool was applied to these houses to analyse how long the holistic application would take to remunerate, with respect to what was feasible practically. The results of this was then used as a basis to develop an optimised solution for each location based upon the conditions inherent in each house, taking into account both energy and economic efficiency. This paper is a review of this process and provides an over of the methodology utilised and results.