In recent years, efforts towards wooden buildings are progressing in Japan. And many woods are used in various places. However, various problems have also occurred in wooden buildings. One of the problems is iron contamination which appears when wood and metal chemically react. At present, tree species that are prone to iron contamination and components that cause iron contamination are clarified. However, the actual weather conditions under which iron contamination occurs are unknown. In this study, conditions of occurrence of iron contamination verified seven test methods. The test method is difference in water quality, difference in temperature, the influence of water entering from the butt end of plywood, the amount of rainfall and iron contamination occurrence time, the difference between sapwood and heartwood, the difference in the distance the butt end and the comparison of how to hit nails. By the results of this test, the water quality and water temperature had little effect on the occurrence of iron contamination within the conditions of this test. However, when the temperature of the environment to be dried was low, the occurrence of iron contamination remarkably decreased. The colour intensity and extent of iron contamination change with rainfall amount. Iron contamination spreads up to the top 10 mm of the nail. The state of the nail after driving the nail into the occurrence of iron contamination does not affect. However, iron contamination did not appear on the surface of the nail implanted deeply into the plywood.

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