The extent of condensation in a dwelling will depend not only on it orientation and construction materials, but on variable factors such as weather conditions, lifestyle, and how the property is heated and ventilated.
The black mould growth in this bedroom is indicative of condensation.There is no obvious physical reason for this.
The control of condensation involves maintaining surface temperatures above the dew point (the humidity related temperature at which water vapour turns into moisture), and the provision of adequate thermal insulation and proper ventilation. Unfortunately, the modern emphasis on draught proofing reduces ventilation in dwellings, increasing the risk of condensation.
Adequate heating and ventilation will help to keep condensation to a minimum. The control of condensation can be significantly improved by installing extractor ventilators in bathroom and kitchen areas with ducts arranged to disperse the humid air to the outside. This will help to remove water vapour at source. The extractors should be operated whenever these rooms are in use.