A New Approach to Winter Moisture Damage Mitigation for the Conservation of Wooden Structures Built inside a Rock Cave
The Center for Conservation Science is conducting research on environmental management for the preservation of wooden structures built inside rock caves, commissioned by Natadera Temple. Natadera Temple, located in Komatsu City, Ishikawa Prefecture, is a religious site where indigenous Hakusan beliefs are combined with Buddhism. Its wooden main hall, designated as an Important Cultural Property, is constructed within a rock cave formed by natural erosion. In such an environment, conditions of high humidity are likely to occur due to moisture supply from the ground and the high thermal capacity of the surrounding rock, leading to risks such as condensation and wood decay.
To date, we have analyzed the causes of the high humidity through long-term monitoring of temperature and humidity within the cave and implemented seasonal ventilation strategies based on these findings. The results have been published in Science for Conservation, No. 65. These measures have led to a certain level of improvement in the humidity conditions within the cave. In particular, during winter, increasing airtightness to suppress the intrusion of cold outdoor air has been found to be effective in reducing condensation on the wooden main hall and lowering humidity levels within the cave. However, reducing the relative influence of moisture evaporation from the ground remained a challenge.
In response, in autumn 2025, a new winter-specific measure was introduced: a simple sheet covering to suppress moisture evaporation from the ground. A follow-up survey conducted in February 2026 confirmed that no problems have occurred so far. Further analysis of monitoring data will be carried out to evaluate the effectiveness of this measure and to propose appropriate operational methods.
The field survey in February was conducted under snowy conditions. Despite this, the interior of the cave was warmer than the outdoor environment, providing an opportunity to experience its characteristics as a natural shelter. Environmental management for cultural heritage requires addressing multiple factors such as climate and site conditions. We will continue to explore optimal environmental control strategies while maintaining harmony with the natural environment.