Moisture infiltration in fractures and consequences on the hygrothermal performance of building facades

Moisture transfer in porous construction materials car-ries many causes for their degradation: mould devel-opment and freeze-thaw damage are favoured by the accumulation of water, and chemicals such as chlo-ride ions and carbon dioxide may accelerate the frac-turing of cementitious composites. Over time, mi-croscopic and macroscopic cracks progressively de-velop under the effects of mechanical loading and sorption/desorption cycles: their influence is to be ac-counted for in long-term hygrothermal performance assessments of the building envelope.
Current simulation codes for heat and moisture trans-fer modelling in building facades do not allow ac-counting for the presence of cracks and defects in the material layers. The present work aims at integrat-ing such effects of damage in simulations at the scale of building facades. Experimental measurements of crack patterns were integrated into a newly developed numerical model predicting coupled heat and mois-ture transfer in multi-layered components. The conse-quences of fractures on the hygrothermal performance of these components were then investigated by com-paring damaged and undamaged materials in a series of simulation cases. Cracks were found to accentu-ate the amplitude of daily sorption/desorption cycles and moisture accumulation in the walls, particularly in case of impacting rain. Their impact on the overall thermal performance is small, although not negligible in case of water infiltration towards an insulation layer.