Performance of a lime-based insulating render for heritage buildings

Insulating heritage buildings in order to provide a comfortable indoor climate, to reduce energy consumption and avoid thermal stresses into the structure, is generally not in accordance with architectural preservation guidelines. Without compromising historic features, insulation renders may however upgrade rendered heritage of which the original materiality is considered inferior compared to its design. This study evaluates the hygrothermal performance of 49 insulating lime-perlite render configurations on brick masonry, by combining characterisation experiments with numerical modelling. The effects of the coupled heat-moisture transport are finally validated by ageing cycles and bond strength tests. It is found that insulating renders cause smaller shifts in temperature in the structure compared to historic renders, but the moisture level of the support may increase significantly. In addition, the insulation layers store a lot of moisture during winter, affecting the expected insulation capacity.