Question
I live in a top-floor apartment in a block built about four years ago and the ceiling of the bathroom keeps getting black with mould. There is no window and just one fan in the ceiling, which is always on when I use the shower. I have tried repainting the ceiling with special paint, but the same thing keeps happening. Is it dangerous and is there anything I can do to stop it?
Answer
What you are describing is a typical case of condensation which results in a black mould growth forming on the ceiling. Generally this is not dangerous. However, the problem could deteriorate with time if not attended to, and prolonged exposure to mould of this nature can be harmful, particularly to people with respiratory problems. In addition to the above, it is obviously quite unsightly and thus it will be in your best interest to cure the problem.
Condensation occurs as a result of a combination of factors including high levels of moisture, poor levels of ventilation, heating and insulation. It is inevitable that bathrooms will give rise to high levels of moisture and thus you need to concentrate on the other three factors. Ventilation is the most important issue. While I would like to see a window to facilitate natural ventilation, it is very typical for bathrooms, particularly in apartment schemes, to be located internally and to have no windows.
The alternative is to have a mechanical extraction fan and I note you have one and that it is used when showering. You will need to check that the fan is powerful enough, particularly if you are a long way from an external wall, and the moist air has to be ducted out for a considerable distance. Particular attention should also be paid to the location of the fan and this should ideally be directly over the shower to be most effective. The fan should also have an overrun facility for at least three to four minutes after showering. This can either be done manually or by fitting a time delay.
The other issue to concentrate on is heating and it is important to ensure that reasonable levels of heat are maintained. The warmer the environment, the less risk of condensation occurring as warm air can hold more moisture vapour. Finally, if the insulation standard is poor, the risk of condensation will also be higher. I note that the apartment is on the top floor where, if the roof is poorly insulated, there will be a higher level of condensation. I would, however, expect that with a relatively new building the insulation standards should be reasonable, and I believe that if the ventilation and heating issues are addressed, it should be possible to keep the situation under control, thereby minimising the condensation and avoiding the formation of the black mould growth.
Val O’Brien is a chartered surveyor and member of the Building Surveying Professional Group of the Society of Chartered Surveyors Ireland