Humidity-controlled warm-air treatment is a method that kills mainly beetles that are damaging the wood. In this process, a heat-insulating and airtight covering is placed around the object building, and the temperature inside the covering is gradually raised to about 60°C, held for a certain period of time, and then gradually lowered. While maintained at 60°C, all forms of damaging insects - adults, pupae, larvae and eggs - are killed. To prevent moisture content changes in the wood and the resulting shrinkage and swelling, the temperature and humidity of the atmosphere are controlled to follow an equilibrium moisture content curve determined by the initial moisture content. In practices, the space is humidified during the warming period and dehumidified during the cooling period. Dehumidification also prevents condensation on the surface of the object to avoid staining. This allows for the elimination of wood-destroying insects without damaging the object. This technique is already being used in Europe and elsewhere for insect control in arts and crafts, furniture, and buildings. In order to apply this method to Japanese cultural property buildings, basic experiments have been conducted since 2008 to confirm the principle, and small treatment chambers and experimental devices that can be used in the field have been developed, followed by demonstration tests using actual buildings in 2017, 2018, and 2022. As a result, the effectiveness and safety of this method were confirmed, and in September 2023, it was applied for the first time in Japan to an important cultural property building in Nikko.

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