Modelling moisture sources likely to occur due to rainwater leakage

Abstract
Moisture control design of building envelope components by hygrothermal simulation is state-of-the-art today. For architects and engineers, there are several simulation tools available which comply with the European Standard EN 15026 and/or the North-American moisture control standard ANSI/ASHRAE 160. Numerous investigations have shown that hygrothermal simulation models are clearly superior to steady-state dew-point calculations in predicting the climate dependent moisture behaviour of construction assemblies. However, compared to real life, there remains a major deficit: most models assume a perfectly assembled and installed building component without any cracks or gaps that may cause unintended moisture entry. This draw-back has been recognized and new approaches have been developed to allow for imperfections by introducing source terms in the models, e.g. accounting for the effects of rainwater penetration. The magnitude of these moisture sources is still a matter of discussion because they should represent best practice situations and not poor workmanship. This paper gives an example of a simplified approach to consider rainwater leakage in one-dimensional hygrothermal building component simulation.