There are two types of rot, dry rot and wet rot. Wet rot is the less serious. This is because it does not spread through masonry and its growth is quickly eliminated when moisture is removed.
However, Serpula Lacrymans, i.e. the true dry rot fungus, is extremely malignant and will spread even through thick walls in search of timber to attack. It is invariably caused by poor building maintenance. Extensive damage can be caused by dry rot and it is important to deal with it immediately.