Many people in Sweden have health problems related to mois-ture in their dwellings. These problems can be avoided if all moisture loads on the building, both water vapour and liquid water, are considered during the design process. This may be done by a systematic Moisture Design of the building. In the Moisture Design process, the moisture con-ditions resulting from all the different moisture loads are calculated and compared with acceptable levels derived from relevant material properties and criteria.

One type of calculation in the Moisture Design process is to predict the risk of condensation at the outer surface of building elements. Four different facing outer walls are studied. The outer climate used is hourly readings during the time-period 1961-90 and a Test Reference Year for one meteorological station in Bromma. The extreme critical year for finding the most frequent occurrence of high relative humidity at the surface was 1990 for walls studied. The drying out potential is normally used for solid construc-tions and it had the lowest value in 1962. The TRY was not appropriate for finding extreme year but may be used for a normal value of the n-factor. The moisture safety factor is calculated by the difference in n-factor between TRY and lowest value. The safety factor fluctuates between 0.4 g/M3 and 0.9 g/M3. The north facing wall has the lowest n and safety factors and therefore it is quite fitting in the Moisture Design process to use this orientation to find out whether a construction is acceptable or not.

• drying potential of building envelope : for wall with no moisture capacity
• Resources: research programs on moisture in building envelope : Lund University program on moisture climate data

1. Estimation of risk of high moisture conditions in an external wall
2. Moisture conditions in a north-facing wall with cellulos loose-fill insulation: construction with and without a vapor retarder and air leakage
3. Moisture control in buildings - how can varying outdoor climate be allowed for?