Condensation is a natural phenomenon which occurs when moist air is cooled to a certain temperature causing the water vapour in the air to change its state to liquid water. Condensation may occur in buildings due to changes in temperature and humidity. In dwellings, condensation on glazings not only obstructs the view through windows but also accelerates the deterioration of paintwork, frames, and furniture. In the present article, a model has been developed to calculate the variation of the nocturnal building temperature provided the external temperature is known. Further, a spreadsheet based software has been developed to assess the frequency of condensation which may occur on any double-glazed window.