Timber may be attacked by many species of wood-rotting fungi, the most widespread in Britain being the True Dry Rot Fungus, Serpula lacrymans and wet rots such as the Cellar fungus, Coniophora puteana and Mine Fungus, Fibroporia vaillantii.

When spores from these fungi settle on damp wood they germinate and develop fine, thread-like filaments called hyphae. Each hypha releases enzymes, which break down wood cells, causing loss of timber strength.

Fungi cannot attack wood at or below about 20% moisture content so decay does not occur unless dampness in buildings arises through poor design or building faults.