Fungal decay always arises because the wood has become wet. Finding the source of dampness and eliminating the ingress of moisture and promoting drying is always necessary.
Outbreaks of dry rot and wet rot start in similar ways. The fungi produce millions of microscopic spores and these are widely dispersed by air currents. If they fall on untreated damp wood they will germinate and grow by breaking down the wood for food. The timber may darken in colour and develop a characteristic cracked appearance. Some wet rots may result in bleaching of the wood; these are more common in doors and window frames. Eventually, the wood loses its strength and in some situations may become dangerously unsafe.