Abstract
One aim of this study is to develop a computerized method for estimating life time of buildings with statistical data. And the other is to make a field research on life time of Japanese houses applying this method. The essence of the life time estimation method is, as we mentioned in the former abstract of this research, just like making human life time tables, but the calculation process is an application of a method called “cumulative hazard method”, which is developed in the reliability theories. We have developed computer programs for estimating the parameters of the distribution functions applied to the observed remaining rate of a cohort of houses or buildings. This program uses least square method on the remaining rate, and is able to choose the most suitable distribution function to the observed data among the normal distribution, the logarithmic normal distribution and the Weibull's distribution. The field research was carried out as sending out questionnaires to the fixed property tax divisions of 48 major cities in Japan. Then we collected the numbers of remaining units and the demolished ones at the year of 1987, grouped by the newly built year. These figures are based on the ledgers of the fixed properties. Selected structural types of the houses are wooden frame or panel, steel frame and reinforced concrete. And the residential types are divided into the detached and the multiple, so we had the data of six house types. And the steel structure office buildings and the reinforced concrete office buildings were also selected additionally as comparing objects to the houses. Defining the life time of a cohort as the time when the half of it will be demolished, we estimated that a cohort of. the wooden detached houses has about 40 year life time, the reinforced concrete about 44 year life time and the steel frame about 34 year life time. As for the multiple dwelling houses, a cohort of the wooden structure has about 33 year life time, the reinforced concrete about 53 year life time and the steel frame about 32 year life time. A cohort of the reinforced concrete office was estimated to have about 33 year life time and the steel frame office buildings about 29 year life time. From these figures, it can be said that Japanese houses and office buildings have similar life times to each other, though that of the office buildings is rather short.
