MODELLING OF MOISTURE CONDITIONS IN A COLD ATTIC SPACE

This study investigates numerically the occurrence and duration of higher relative humidities in a cold attic space, which are a consequence of the excessive moisture supply from the ventilation of the attic and from the infiltration of air from a dwelling. Hygrothermal states of the attic air zone and of the adjacent construction elements are calculated by a whole building heat, air and moisture simulation tool. Airflows to the attic are determined by taking into account the total distribution of pressure around and inside a building. The role of the attic ventilation is analyzed by comparing naturally ventilated and unventilated attics in an open landscape or in a city zone. For the air infiltration from the dwelling only scenarios with the airflow directed mostly to the attic are analyzed. The simulations show that, if indoor air infiltrates through the attic floor, it is necessary to ventilate the attic. In that case, a building situated in a sheltered position is more susceptible to moisture problems in the cold attic compared to the same building in an unsheltered position. However, in the absence of the air infiltration from the dwelling, the attic should not be ventilated. Simulations are performed for real climatic conditions