Capillary active interior insulation: do the advantages really offset potential disadvantages?

Abstract

Nowadays, capillary active interior insulation systems are often promoted because of their ability to avoid interstitial condensation, while a drying out remains possible. Additionally, their alleged performance to regulate the indoor climate is often used as a selling point. This paper compares the hygrothermal performance of a capillary active interior insulation system to this of a traditional vapour tight system. Where the previous studies on capillary active insulation systems mainly focused on historical buildings, this study investigates the applicability to standard single leaf masonry walls. Apart from the risk on interstitial condensation, also the impact on the indoor climate and the impact that wind-driven rain has on the hygrothermal behaviour of the retrofitted wall have been analysed. The capillary active system is found to be more sensitive to small modifications of the wall structure (e.g. interior finishing coat, wall thickness), while hardly any differences could be observed for the wall with a vapour tight system. In addition, wind-driven rain can hamper a good hygrothermal behaviour of a capillary active interior insulation system by inducing a lower thermal resistance or an increased indoor relative humidity. Therefore, it should be checked if the advantages of using capillary systems offset the potential disadvantages. A case-specific study is recommended to ensure the applicability of a capillary active interior insulation system.