Hygrothermal assessment of solid masonry walls internally insulated with bio-based insulation materials

This study investigated the hygrothermal performance and risk of mould growth in two bio-based thermal insulation systems for internal retrofitting purposes; loose-fill cellulose insulation and hemp fibre insulation. The experimental set-up comprised a 40-feet (12.2 m) insulated reefer container with controlled indoor climate, reconfigured with several holes (1x2 m each) containing solid masonry walls with embedded wooden elements on the interior side and different internal insulation systems, with and without exterior hydrophobisation. The container was placed in Denmark. Throughout 1 year and 2 months, temperature and relative humidity were measured in the interface between the masonry and the internal insulation and in the embedded wooden elements. The effect of exterior hydrophobisation was also investigated. The VTT mould growth model was used to evaluate the mould risk. Lastly, the hygrothermal performance of the bio-based systems was compared with that of previously examined inorganic internal insulation systems. Findings for the two bio-based thermal insulation systems showed that exposed walls experienced high relative humidity. The combination with exterior hydrophobisation to lower intrusion of driving rain had a positive effect on the moisture balance for the masonry walls. However, the insulated walls with hydrophobisation still showed high relative humidity levels during specific periods of the year in some of the examined masonry walls. The mould risk evaluation showed a high risk of mould growth in masonry/insulation interface, as well as in the wooden wall plates in some test walls.