ABSTRACT
When building materials and components are transported, stored on site and used in a structure, they are subjected to the effects of a number of agencies, some of which may influence adversely their durability and performance and, thereby, have a major bearing on the possibility of their premature failure. The action of the weather, or the external climate, is foremost amongst these. It is often taken to affect only those materials exposed externally. However, the distinction between the external and internal environments in a building is not always clear-cut. There are partially protected areas still open to the weather to some extent. Outside air enters a room through an open window and sunlight is filtered through window glass. Weather changes in protected or internal environments are usually the same in type but slower in action than those taking place outside. Buildings themselves cause modifications to the weather and to the microclimate, considerable differences in which may occur in quite short distances. The micro-climate is, indeed, of particular significance and, because of the large number of individual circumstances which can cause its modification, is still an area of much uncertainty and a fruitful one for detailed investigation.
