An evaluation of the effects of contemporary interventions on the environmental behaviour of traditional local buildings : a study of unmodified and modified traditional lime-mortar-roofs (Malta)

Abstract

This dissertation investigates the behaviour of “Deffun”-mortar roofs in the presence of moisture, under simulated Maltese climatic conditions, for both traditional and modified roof assemblies. Laboratory tests on total porosity, water absorption by capillarity, vapour diffusion and hygroscopic sorption were conducted to investigate the hygric properties of the main materials which form part of traditional roofs: “Deffun”-mortar, “Torba” and “Stone”. The resultant material properties informed Numerical simulation models. WUFI®Pro was adopted to investigate the hygrothermal behaviour of Multi-layer assemblies representing the traditional roof build-up. These were compared to modified Multi-layer roof models which included the addition of an impermeable roofing bituminous membrane at the top of the “Deffun”-mortar layer. The results show that the traditional roof model favours the retention of moisture in the uppermost layers during the wetter periods. It allows time for water within the surface mortar to be mobilised upwards by capillarity, with the aid of external temperature and wind, and evaporate preferentially towards the outside rather than the interior of the room. When modified using waterproofing membrane, the moisture managing capacity of the roof decreases with increasing resistance of the membrane layer to the outward flow of moisture. Any defects in workmanship or cracks at the surface of the roof will result in significant increase in the overall water content of the assembly and higher moisture levels within the bottom Stone layer. Consequently, this increases the risk of dampness and mould growth within the internal habitable areas and possibly the loss of internal finishes when present.