As a heat transfer coefficient of external surfaces of a building, about 16 kcal/m^2h℃ is now used in Japan. Yet the value is said to be too large in the sunnier. When the above convective heat transfer coefficient is used, the sol-air temperature is presumed on the quite low side, which is on the critical side in the view of the cooling load. In this respect, Dr.Kimura suggested a convective heat transfer coefficient of 10 kcal/m^2h℃. In order to obtain the value experimentally, the method of measuring the convective heat transfer coefficient with a SAT meter and the pyrradiometer was devised for this study, and the convective heat transfer coefficient of the rooftop surface exposed to solar radiation at a low wind in summer was mainly examined through experiments. As the result, it has been made clear that, when the wind velocity is 2 m/s or lower in the daytime in summer, the convective heat transfer coefficient of the rooftop surface ranges from 7 to 8 kcal/m^2h℃.
