Thermal performance of a selection of insulation materials suitable for historic buildings

Abstract

Improvement in the thermal performance of the historic building stock has the potential to reduce building operational energy and its associated negative impact on the environment. Currently, there is a lack of knowledge on the performance of traditional solid walls and the impact of internal insulation on their hygrothermal behaviour.This paper investigates the in-situ thermal performance of seven internal insulation options, on a historic brick wall, using heat flux sensors (U-value measurement), thermal imaging survey and internal wall temperature. The insulations include thermal paint, aerogel, cork lime, hemp lime, calcium silicate board, timber fibre board and PIR board. Their performance is compared to a traditional lime plaster finish. Additionally, their density and specific heat capacity is measured in the laboratory.The brick wall with lime plaster (c.840 mm) has a higher U-value of 1.32 W/m2K than expected. All the internal insulations were found to reduce the U-value of the wall (between 34 and 61%) with the exception of a thermal paint which had no effect. The thermal imaging survey corroborated the U-value results, and insulations with low wall U-values also had high wall surface temperatures. Internal wall temperatures showed a similar trend; a reduced temperature at the wall/insulation interface for low thermal conductivity insulations. Lastly, the in-situ insulations underperformed when compared to their manufacturer's specified properties (wall U-value higher by 13–25% with the exception of cork lime). This is attributed to real in-situ environments compared to ideal testing laboratory conditions.