We wish this study enable us to select a suitable construction method of the external wall in cold district. We set up several ALC external walls in several conditions of outdoor temperature and indoor humidity, and measured the quantity of vapor flowed into the walls from indoor and the quantity of internal vapor condensation of the walls. As a result, when the outdoor temperature changed with one day period, the lower the maximum outdoor temperature, the more the quantity of the internal vapor condensation. And we knew the vapor flowed into the wall had a tendency to concentrate in the freezing area of the wall in case of the change of the outdoor temperature.
