For the prediction of chemical pollutants emission rate from building material, the data of effective diffusion coefficient are important and indispensable. In this research, cup method is used for measuring effective diffusion coefficient in various building materials for various VOC. The targeted VOC (Volatile Organic Compounds) was placed in a cup, which was tightly sealed with a building material placed over the opening. The VOC in the cup moved out of the cup only by diffusing through the building material. The cup was placed in a constant temperature chamber, and the VOC concentration at the upper portion of the cup exterior (upper face of the building material) was maintained at zero by a large ventilation rate. The building material lower face (that is, in the cup) was in a vapor phase concentration under the saturated vapor pressure of the VOC, which determined the concentration gradient in the material. The emission flux was measured by measuring the changes in mass of the VOC in the cup. The diffusion coefficient was calculated from the emission flux and the concentration gradient in the building material. In this research the effective diffusion coefficient of VOC were estimated at about 1.0×10^<-7> [m^2/sec] for various building materials
