<p> This paper addresses the use of CLT siding usage and its effect on the thermal environment to better understand the possibilities for wooden structures for public buildings, in particular school facilities. Results and findings of this research are as follows:</p><p> 1. Measurements of the thermal environment during cold and hot seasons of buildings:</p><p> One building utilizing CLT on the external, southern-exposed wall for thermal enhancement was used for measurements, and another building with the CLT was used for measurements and comparison to understand the inside thermal environment. For the basic experiment during the winter season, it was found that the building with CLT used on the external walls experienced a gradual change in room temperature as opposed to the sudden changes in temperature noted outside. During the summer season, it was noted for the same building that though the room temperature was initially recorded as high, with the use of air conditioning, the room temperature was able to drop to a comfortable level. After the air conditioning system was turned off, the change in the room temperature was gradual. In regards to the other building, the natural temperature of the room as well as the globe temperature were basically the same, and in comparison with the outside temperature, little change in temperature over the course of a day was noted. Furthermore, the humidity in the room throughout the day fluctuated little if any. These findings, when charted, were found to be quite similar to those of the building with external CLT usage.</p><p> Also, the actual measurements and findings from the experiments were found to be similar to those determined by simulations and calculations resulting from the use of the LESCOM-mint computer simulation program.</p><p> 2. Comparison of RC and CLT buildings in seven different climatic regions</p><p> We considered medium to large sized wooden structures, in particular public school buildings, for our simulations. As the majority of public schools are RC buildings, we used the RC building model and compared it with a CLT model and considered the heating and cooling load for seven different climatic regions in Japan. We found that the cooling load for both the RC and CLT models were similar throughout all seven regions; however, when considering the heating load for the two types of buildings, we found that the CLT model had a lighter heating load than the RC model. From this comparison, we determined that CLT building model was superior for heating and maintaining the warm environment in the cold season.</p><p> 3. Differentiation in CLT thickness in seven different climatic regions</p><p> We calculated the differences in heating and cooling loads for a typical classroom in the seven different regions. In each area except Naha, the change in cooling load due to the difference in CLT thickness is small.</p><p> On the other hand, the heating load is reduced by 16 to 20% for CLT 60 mm with respect to CLT 10mm, and is further reduced for 4 to 6% for CLT60 mm for CLT 90 mm. Even if the thickness is increased by 30 mm after CLT 90 mm, the reduction rate is small.</p><p> When comparing these findings with the RC simulations, it was further noted that if the CLT was 60 mm or more, the heating / cooling load was slight, and even if the CLT’s thickness was increased, a significant change in the load was not noted. CLT was found to be highly more efficient than RC in absorbing heat, thus helping to reduce the heating load while maintaining a comfortable room environment for work or study.</p>