Hygrothermal assessment of diffusion open insulation systems for interior retrofitting of solid masonry walls

The present project investigated the hygrothermal performance and risk of mould growth in solid masonry walls fitted with three diffusion-open capillary active interior insulation systems installed in containers with a controlled indoor climate. The project was carried out as a large experimental study in two 40-feet reefer containers reconfigured with 24 holes (1 x 2 m), in which solid masonry walls with embedded wooden elements were installed. The focus of the study was on the conditions in the interface between the masonry and the interior insulation, and in the embedded wooden elements. The effect of exterior hydrophobisation was also investigated. Relative humidity and temperature were measured at several locations in the test walls over a period of four years. The findings indicate that exposed walls with interior insulation and high indoor RH performed poorly in terms of the risk of mould growth. Combined with exterior hydrophobisation against driving rain, the semi diffusion-tight insulation system performed better than the highly diffusion-open systems. Good performance was observed for the semi diffusion-tight polyurethane foam insulation with calcium silicate channels combined with exterior hydrophobisation. The effect of hydrophobisation varied with the orientation. Mould observations found no growth in the interface in most walls, probably because the high alkalinity of the adhesive mortars and scarce nutrition prevented growth. Growth was however found in some walls having low alkalinity and possibly available nutrition. Little correlation was found between on-site and modelled mould growth.