This article aims to determine the dynamic thermal performance of a room . The internal temperature as well as the thermal load for walls and rooms were determined using a modified form of the thermal time constant method. The effect of building materials ,volumes ,orientation ,depth, ventilation mode ,seasons and exposure area on both internal temperatures and thermal load are studied. A suitable design is given to verify different desired thermal conditions towards energy conservation. A simple method is introduced to get the internal wall temperature and the wall thermal load from a chart based on the wall thermal time constant. Correlation are also given to get the most suitable room depth for each building material depending on the enclosure volume and on the enclosure thermal time constant. The study showed that the increase of the thermal time constant leads to conserving the thermal response.