Abstract
Interior insulation can improve energy performance in historic timber buildings but may increase moisture risk by cooling existing layers and limiting drying. This study combines large-scale measurements and calibrated 1D WUFI simulations to evaluate moisture behaviour and mould risk in historic timber plank walls. Four wall specimens were monitored in the ZEB Test Cell in Trondheim: three interiorly insulated woodfibre variants with either a moisture adaptive or conventional vapour barrier and one uninsulated reference. Temperature, relative humidity and timber moisture content were measured continuously; results from the first 14 months are reported. The calibrated model was used for parametric studies under recent historical climate, design-years and future climate scenarios, and mould risk was assessed using the VTT Mould Index. All test walls dried during the first year, but the conventional barrier showed a stronger summer moisture increase, consistent with inward-driven moisture transport and limited inward drying. The VTT Mould Index results indicate that mould risk is governed primarily by initial moisture condition and indoor moisture load; future climate scenarios increase risk for the reference wall, particularly under high indoor humidity, while internally insulated variants generally remain low-risk under normal indoor moisture load (assuming adequate airtightness).