Evaporative damp in hygroscopic environments : An overlooked moisture mechanism in applied building survey practice

Abstract

Evaporative damp is proposed in this paper as a distinct and under-recognised moisture mechanism in building survey practice, defined as the sustained release of moisture from previously wetted building fabric into the internal environment, where it is absorbed and re-released by hygroscopic materials. Although the underlying physical processes are well established, current diagnostic frameworks do not recognise fabric evaporation as an independent internal moisture source, leading to repeated misdiagnosis and ineffective remediation. The paper demonstrates how moisture stored within porous materials continues to evaporate over extended periods, sustaining elevated humidity, condensation, and mould growth independently of occupant behaviour. Two field case studies illustrate the mechanism under contrasting conditions, including a vacant property with no internal moisture sources and a ground-contact substrate acting as a continuous moisture emitter. The findings highlight the limitations of standard survey tools, which are unable to quantify residual moisture burdens or distinguish between moisture sources. The paper argues that visible indicators of prolonged structural dampness should trigger recognition of evaporative damp as a concurrent condition. A revised diagnostic and remediation protocol is proposed, including a managed drying phase based on active dehumidification. Recognition of evaporative damp enables improved diagnosis, clearer communication with occupants, and more effective long-term moisture management outcomes. This article is also included in The Business & Management Collection which can be accessed at https://hstalks.com/business/.