In this paper, firstly the author shows that the numbers of freezing-and-thawing cycles and the freezing temperature are the most important as factors for frost damage of the external materials in wiu region.
Secondly the numbers of freezing-and-thawing cycles at 30 cities in the Tohoku District are calculated using statistical climatic data.
According to the considerations of the numbers of freezing-and-thawing cycles and the other climatic elements as the factors of frost damage, it was appeared that the numbers of freezingand-thawing cycles are greatly related to the Oligo snow fall rate (KASETSU-RITSU in Japanese), and the minimum mean temperature, and the numbers of freezing-and-thawing cycles are calculated approximately with the regression equations.

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Return period conversion coefficients for design snow load are calculated. Used data are annual maximum snow depth and annual maximum increasing intensity of snow depth in 7 days. Those are observed on 423 stations belonging to the Japan Meteorological Agency. The coefficient is applied for control of the reliability on design by converting period into adjusted load value. The coefficient is expressed by the gradient of a line on the Gumbel probability paper. Therefore, the coefficient is calculated from the mean value of ratios of the value associated with return period of 200 years to the value that of 100 years on each observation point. The ratio is small in heavy snow area compared with that of light snow areas. Therefore, the return period conversion coefficients are set for two categories of snow depth associated with return period of 100 years.

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