Sick building syndrome, which has become a major public concern in recent years, is caused in part by volatile organic compounds (VOCs) emitted by building materials. In order to ensure the safety of our environment, it is necessary to predict indoor VOCs concentrations over a long period of time. Long-term prediction of VOCs concentration requires the consideration of the influence of temperature changes, and there is a need for a simple prediction method that can be used for this purpose. The prediction methods that have been proposed thus far, however, do not meet this requirement. In order to develop a reliable prediction method, therefore, it is necessary to investigate the temperature dependence of the emission factor and accumulate data on a wide variety of building materials. This paper briefly describes the proposed simple long-term prediction model that considers the temperature dependence of building materials. To consider temperature dependence, the concept of "equivalent material age" is introduced as a parameter for the acceleration or deceleration of emission due to temperature changes. An example of an analysis using the method and concept mentioned above is also shown. The next report (Part 2) will outline the verification experiment conducted for the purposes of this study and describe the results of comparative verification results.