Hygrothermal performance of ventilated attics: A field study in cold climate

Ventilated attic constructions have long been considered reliable designs for cold climates. However, concerns have arisen due to climate change, high thermal insulation levels, and instances of detected mould damage in specific locations. To address these issues, we conducted a study involving six different well-insulated, wooden, ventilated attic constructions within purpose-built test buildings. These structures employed two distinct ventilation solutions, two types of underlay materials, and two thermal insulation materials. During the test period, none of the structures exhibited condensation or visible mould growth. The calculated mould indices remained well below 1, indicating good hygrothermal performance. The two attics with the lowest air change rates also had the lowest average relative humidity levels and mould indices. Based on our findings, there is no need to maximize the air change rate in ventilated attics for cold climates; instead, determining an optimal ventilation rate is crucial.