We often get asked to look at mould problems, particularly toward the end of winter. Mould will grow when the ceiling or wall is damp from condensation or a roof leak and stays damp for a period of a few days or more. In Sydney we had a very wet week back in July. South facing walls or other parts of the house that stayed damp were prone to mould growth. Most of the mould I looked at was not caused by a roof leak. “Roof leak” mould tends to be in isolated spot and usually causes some minor damage to the ceiling as the drip from the roof works its way through the ceiling. Condensation type mould usually starts as spotty over a wider area and can quickly spread and become heavier. Ceilings can become completely covered in this mould and in this situation it is almost never a roof leak that is causing the mould to grow.