To understand the impact on the thermal performance of a Victorian end-of-terrace house and the risks of moisture accumlation after fabric improvements, Historic England carried out whole house thermal performance testing and monitored the moisture conditions at the wallinsulation interface of two internal wall insulation systems on the solid brick walls of the house. Monitoring has been ongoing since December 2011 until January 2019 and the in-situ data has been compared with hygrothermal modelling using WUFI Pro5. The principal goals were to facilitate informed decisions on improving the energy efficiency of traditionally constructed buildings and to understand the potential benefits and unintended consequences of different kinds of adaptation to reduce that energy use, in particular technical risks due to moisture.