Impact of Moisture-Buffering Materials and Time-Averaging of Infiltration Rate on Prediction of Indoor Air Humidity

The moisture buffering properties of materials and actual air exchange are crucial for indoor conditions in buildings. Consequently, precise material data and an adequate model of highly variable outdoor air infiltration are essential for computer-based design simulations. This study quantifies how internal cladding materials and infiltration time-averaging affect indoor relative humidity prediction. Three internal finishing variants were analysed: painted gypsum plasterboard, painted clay board, and unpainted clay board, the latter characterised experimentally by a practical moisture buffer value of 1.88 g/(m2·%RH). Three moisture-load scenarios were considered, resulting in 27 simulation cases. Hourly infiltration rates were calculated in the DesignBuilder software and then converted into annual, monthly, and daily averages for WUFI Plus 3.X simulations. The annual mean infiltration rate was 0.117 h−1, while selected daily means ranged from 0.03 to 0.60 h−1. Passive moisture buffering, especially the unpainted clay board, reduced short-term RH fluctuations but did not entirely compensate for insufficient moisture removal. Surface finishing has a decisive influence on the practical performance of hygroscopic materials. Under high moisture gains, median RH reached about 69.5%, and predictions became sensitive to infiltration resolution. Annual averaging may therefore be sufficient for low moisture loads, whereas daily values are required when short-term moisture peaks and moisture buffering effects are relevant.