Abstract
A mock-up, one-story test house with eaves ventilation was built in a suburb of Tokyo to examine the hygrothermal conditions in its attic space. A series of measurements were conducted to clarify the effects that the vent opening area and vented wall cavity had on the hygrothermal conditions. In addition, to estimate the airflow rate through the vented wall cavity and eaves vent using the air velocity measured by an anemometer placed therein, the relationship between them was measured by changing the fan flow rate in an experimental setup. The dehumidification of the attic space by the eaves vents, vented wall cavities and room was calculated during the experimental period. The main findings are as follows: 1) Of the total flow rate through the vented wall cavity on the southern side, the proportions among upward flow into the attic space, upward flow into the ventilation opening, and downward flow were approximately 5:1:4. 2) Considering that 20% of the upward airflow through the vented wall cavity did not contribute to the ventilation of the attic space, the eave space should be added as a calculation node for hygrothermal models to predict the proper size of the attic ventilation opening. 3) Glass fiber insulation wrapped a vapor tight film (bagged insulation) is generally employed as a insulation layer of ceiling in mild climate regions of Japan. The air gap between the insulation materials has an impact on moisture flow passing through the ceiling gypsum board to the attic space.
