Moisture control in buildings - How can varying outdoor climate be allowed for?

This paper describes the general need for secure protection against moisture, and methods for designing the structure in this respect. Ensuring that all the possible moisture loads on different parts of a building have been systematically considered creates the right conditions for designing structures without moisture problems. An important part of the work of designing structures to deal with moisture loads is to estimate the risk of damage and problems resulting from random variations in the properties of materials, in indoor and outdoor climate and in user/occupant habits. This paper describes, in particular, the effect of a varying outdoor climate and methods for allowing for it when calculating the moisture conditions of various parts of a building and the corresponding reduction in performance of materials and designs. By performing calculations for a number of cases over many years (1961-1990) and by studying the spread of the results from one year to another, it is possible to identify the reference (average) year and the most severe (extreme) year. With this information, appropriate safety factors for design calculations can be determined. The paper describes calculated moisture conditions and presents examples of design safety factors for moisture problems encountered in different types of designs.