In the past, the external exposure dose model for soil (the soil’s physical model) was used to calculate the doses of decorative building materials because there was no materials model. In this paper, physical models are proposed to calculate the absorbed dose rates in air from decorative building materials by Monte Carlo simulation with the EGSnrc code. The physical models of this paper greatly differ from physical models for soil. The good agreement between simulations and measured absorbed dose rate in indoor air indicates that the results obtained by the Monte Carlo simulations are realistic. The absorbed dose rates in air calculated by physical models for soil are much higher than the measured dose rates. According to the reports of UNSCEAR 2000 and ICRP 1999, the limits of radionuclides in some kinds of decorative building materials were deduced by using the physical models for materials presented in our work. The limits of every kind of decorative building material from our work are different.