Probabilistic modelling of hygro-thermal performance of building structure

A probabilistic model of the hygro-thermal performance of the internal surface of an external wall is suggested. Particularly, the daily exceedances of the critical value of relative humidity on the surface during the first year of its transition from 'as built' state to the quasi steady state are studied. The time dependent internal/external loads are represented by one concrete realization, related to the climate parameters of the site and the activities of inhabitants. Three selected material functions-water vapour permeability, moisture diffusivity and thermal conductivity are described by random variable parameters. The probabilistic model relates to the deterministic 1D simulation of heat and moisture transfer through the building structure, which has been algorithmised in the code NEV3. The values of relative humidity resulting from NEV3 calculations are analysed for daily durations of the critical threshold exceedances. Employing the Poisson spike process, the first-passage probability of exceeding a considered duration, conditioned by the actual values of the material parameters, is determined. The total probability is calculated by FORM.