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. In the UK six properties are to be studied through: software analysis of energy consumption and in-house monitoring both pre and post install of retrofit technologies. This paper presents the first stage in the process in which a series of terrace and semi-detached houses are analysed using Design Builder dynamic simulation software. Various designs and methods of retrofit (Insulation, HVAC, etc) are analysed and the energy savings on a baseline are calculated. It was found that there are limitations in terms of what it practicable, and what energy savings are possible, in relation to insulation thickness when very low U-values are adopted for retrofit.