The ageing of building stock is becoming an increasingly urgent issue in several more developed regions. It is like an ageing population in which buildings last a long time, reducing the rate at which they need to be replaced and calling for more retrofitting and rehabilitation. In Europe and the US, ageing building stock has caught the attention of policy makers and researchers, who want to improve the energy efficiency of existing, old building stock. Old and dilapidated buildings are urban time bombs, especially those in high-density built environments. To find how long buildings will last is essentially a survival analysis of buildings. Although seemingly straightforward, the age of a building at a given time and the actual life span of a building must be clarified. To express the survival rate of buildings, the median survival time is used or the length of time when half of the buildings under study are expected to survive.