Retrofit of hard to treat properties has been highlighted as a policy challenge to reduce energy consumption in the UK. This study undertook an experimental staged retrofit of a pre-1919 UK solid wall property under controlled conditions. The property is housed within an environmental chamber, where the conditions were held at a constant 5 degrees C during the test to reflect UK average winter temperature, with all other boundary conditions removed. The retrofit was undertaken using commercially available products and at each stage a number tests were conducted to evaluate the performance, with the results for the coheating tests and in situ U values being reported here. The results show that the deep retrofit undertaken led to a 63% reduction of heat loss from the building, with the technical feasibility of staged retrofit clearly demonstrated from a heating energy efficiency perspective. The calculation of cost savings suggests that a whole house deep retrofit may not be financially feasible if supported only by energy savings. The use of controlled conditions did allow each stage to be measured and compared in a way that has not been achieved in the field, allowing for effective comparison of each stage previously only fully explored in models. There are limitations of the methodology driven by the lack of boundary conditions, specifically around air movement and longer term performance issues, which are best addressed in the field. (C) 2017 Elsevier B.V. All rights reserved.