Condensation Targeter II: Modelling surface relative humidity to predict mould growth in dwellings

Condensation and mould growth are reported as being problems in an estimated 4.2 million dwellings in England, resulting in poor health for the occupants and substantial damage to the fabric of the building. This paper examines the development of an algorithm, Condensation Targeter, to predict the relative humidity of internal surfaces and risk of mould growth in dwellings. The impacts of cold bridging, seasonal variations, variable moisture production and hygroscopic materials are reviewed (but not of interstitial condensation) and a comparison between modelled and measured data for 36 dwellings is carried out. Results indicate that a steady-state model utilising Bredem-8 to predict internal temperatures and Loudon's condensation model to predict moisture shows good (± 10%) agreement with monitored data. A model sensitivity study shows that variations in occupant heating and density can be as important as, or even more important than, ventilation in determining mould.