Mineral fibre filled cavity wall: Hygrothermal properties

Summary An experimental study of the heat and moisture transfer processes in an insulated cavity wall was carried out under controlled steady-state winter conditions applicable to the UK, in a wall laboratory at Salford University. The overall test area of each wall, between the indoor and outdoor climatic chambers was 3 m x 3 m. The principal objective was to study the thermal performance of the wall and the effect of moisture. Other objectives were to locate regions of interstitial condensation and compare with theoretical predictions, and to compare the actual performance with that predicted. In the cavity wall filled with mineral fibre, moisture was found to have a negligible effect on the thermal conductivity of the insulant and a small but predictable effect on the concrete block inner leaf. The variations in thermal conductivity of the concrete could be explained in terms of the moisture content profile, which in turn could be explained, to a large extent, by the hygroscopic moisture present under the prevailing relative humidity distribution. Under ’wet ’ conditions, where interstitial condensation is predicted to occur, saturation conditions were detected and these were found to be restricted to the brick/insulant. The measurements support the current theory that condensation tends to be restricted to the interface. Measurements of relative humidity in the cavity were broadly in line with those predicted by current theoretical models. The overall measured thermal performance was in line with normally accepted values.