Fuktsäkerhet i ventilerade parallelltak

Sammanfattning: Parallel roofs are commonly used in Sweden when constructing new small house buildings and are also difficult to access for inspection. Furthermore, high demands are set in the Swedish building regulations, although there are no clear guidelines for their compliance. Many previous studies investigating moisture safety in parallel roofs applies a constant air exchange in the ventilated air cavity. In studies where calculations are compared with measurements, it is rarely done blindly. This study aimed to investigate the described problems, in a parallel roof ventilated from eave to eave, by examining how the varying air flow in the cavity could be modeled and the relevance of considering this variation in coupled heat and moisture calculations. The accuracy of moisture safety assessments using blind calculations (without knowledge of measurement results) in WUFI Pro (2019) were also studied. The results of the study indicated that it was possible to get high resemblance with measurements when using an air flow model for the air exchange in the cavity and applying that model to blind hygrothermal calculations. When real conditions are sought in blind calculations, this study identified that knowledge about the initial moisture content, material parameters for the investigated materials and the degree of shading, as the most important parameters for high compliance. To ensure moisture safety in a parallel roof, a water- and moisture proof construction in combination with the outdoor climate were identified as the most important parameters.