Drying Potential of Cold Attic Using Natural and Controlled Ventilation in Different Swedish Climates

Problems with high humidity levels and mold growth in cold attics have been increasing over the last few years. The high humidity levels are to a large extent a consequence of the increasing demand on energy efficiency. Houses are frequently retrofitted with additional attic insulation, which leads to a colder attic space and hence a higher humidity. Replacing furnace heating by heat pumps or district heat may also lead to problem. Also newly built attics have problems. The quite novel technical solution with controlled mechanical ventilation of the attic is generally estimated to be risk free in Swedish climate. With controlled mechanical ventilation the attic is intentionally ventilated only when the inflowing air is drying out the attic, otherwise it is shut off. The drying potential of controlled ventilation is analyzed for different climate zone in order to map the relative efficiency compared with traditional natural ventilated attics.