Post-works assessment

Owner’s feedback

At the time of the study, the owner had been in the house for one winter heating season following the works. A dramatic improvement in thermal comfort levels and a high degree of satisfaction with the improvements were noted. The boiler is now programmed to a much reduced heating cycle and it was described that the house “feels like it is heated even when the heating is off”. This is likely due to the fact that the thermal mass of the walls is exposed internally and is re-emitting heat absorbed and stored during the heating cycle.

Impact on BER rating/fuel bills

The BER of the building has been improved from an F to a D1 following the works. The BER would indicate that the heating energy load of the house has theoretically reduced by 35%.

Only one set of bills for each of the two-month April – June periods before and after the works were available, which indicated a dramatic reduction of energy consumption of more than 50% and cost reduction of 41% despite an increase of gas prices of 13% during the intervening period. It is noted however, that the 2011 bill was based on an estimated reading and the variables noted in other case studies (e.g., Belton Park) could also affect the results.

The dramatic impact of the works illustrates the benefits of retrofitting wall insulation to detached houses that have a large external wall heat loss area (See section on Heat loss form factor [link to follow]). The external insulation works in this instance appear to have had a much greater impact than the compact terraced Belton Park Villas case study. This is due to the fact that this house has proportionally a larger area of exposed wall that is losing heat. The upgrading of the walls therefore had a greater impact on the performance in addition to the fact that a greater thickness of insulation has been applied.

Impact of works on architectural heritage

The works included the removal of original brick-and-plaster façade features that were part of the defining character of the house. Although the features have been accurately reproduced over the external insulation layer, the conservation principles of minimum-intervention, repairing rather than replacing and honesty of repairs & alterations are called in question. The works also have had a visual impact in terms of the depth of window reveals, the depth of the roof soffit and the over-cladding of the window cills with powder coated aluminium cills. The works therefore can be deemed to have had a significant impact on the architectural heritage value of the house.

Nevertheless, this study attempted to define where external insulation works to pre-1945 houses would be acceptable. The house was not deemed to be as sensitive as other 18th- & 19th-century case-study dwellings that were examined. The works to the façade of the house have been carried out accurately and with high-quality workmanship (see images). The fact that the house is not terraced and does not have a well-defined context of similar houses in its vicinity, mitigates the visual impact of the works.

This case study serves to illustrate what can be achieved, but it is highlighted that the works were supervised closely by its architect owner when they were being carried out.