This paper aims to describe estimation methods of life span of buildings through register research of "K" city. The registered data are Total Floor Areas (T. F. A.) of existing buildings, dismantled buildings, and completed buildings. In this paper, life span is estimated by applying the following four distribution functions ; (1) Normal Distributio, (2) Logarithmic Normal Distribution, (3) Weibull's Distribution, and (4) Gamma Distribution. The estimation methods of life span of buildings are as follows. 1) The age distribution of dismantled buildings, with the T. F. A.'s data of the dismantled buildings and of completed buildings were used in the estimation of life span (of buildings). 2) The age distribution of existing buildings, with the condition that T. F. A.'s of the completed buildings are constant. T. F. A. data of the existing buildings and of completed buildings were used in the estimation of life span. The results are summarized as follows. 1. The distribution of the life span of buildings approximates that of Normal Distribution and Weibull's Distribution. 2. Using the two methods, the average life span of public buildings of "K" city is estimated to be 35-38 years.
