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The risk of condensation in cold pitched roofs is dominated by airflows from the living areas of a house into the loft and through the loft to the outside. The effect of these airflows is excluded from the current British Standard procedure for assessing interstitial condensation risks. This paper discusses the factors that are necessary to construct a realistic model to predict condensation risk in structures with significant airflows, and describes the sources of the data needed to run such a model and the resulting outputs.
A table gives typical thermal and vapour transport properties of common roofing materials. Hourly values of temperature, humidity, wind speed and solar radiation are needed to represent the external climate, but can be difficult to acquire in sufficient detail. If the effect of long wave radiation is ignored, the risk of condensation will be seriously underestimated. 12 pages.