A whole life, national approach to optimize the thickness of wall insulation

Insulating external walls has great potential to reduce post-retrofit operational energy consumption and thus carbon emissions, but determination of the optimal insulation thickness still remains a challenge in the building industry. Although life cycle performance assessment has been introduced into the optimization of wall insu-lation thickness, there is still a lack of studies conducted at the building stock level. Moreover, the impact of variations of future climate conditions and the carbon intensity of the electricity grid are rarely studied. This study aims to fill this gap, by developing and demonstrating a holistic whole life approach to determine the optimized wall insulation thickness of the English housing stock. The study assesses both the reduced post -retrofit operational energy and carbon, as well as the additional embodied energy and carbon from wall insu-lation. There are three different optimization aims, namely: maximize the whole life carbon emissions reduction, maximize the whole life energy consumption reduction, and maximize both the whole life energy consumption and carbon emissions reduction. The results revealed that the optimized glass wool insulation thickness varies from 0.010 m to 0.275 m, increasing wall insulation thickness further than optimized value will result in negative effects. Ignoring future variations could lead to overestimation of the reduction potential of insulation instal-lation on whole life energy consumption, and thus emissions reduction. The overestimation percentage for stock level whole life energy consumption reduction varies from 20.5% to 26.7%, and the overestimation percentage for stock level whole life carbon emissions reduction varies from 421.3% to 502.0%.