Clients ask me "What is dry rot?" a lot.
Presumably because they're not sure of the differences between wet and dry rot, and with timber forming large parts of our homes and the current trend towards kit homes and the popularity of timber frame homes in the 1980’s and 90’s they’re right to be concerned about rot to timbers (including wet rot as well as dry rot).
What is Dry Rot?
Dry rot is a fungus that grows in timbers once the timber reaches a certain moisture content. The general consensus is that timbers are prone to damage if the moisture content gets above 20% however dry rot, once established, can spread at moisture contents as low as 14-15%. Although it is generally accepted that for an outbreak to start the moisture content needs to be between 20-35% (wet rot generally requires timbers to have a moisture content of 40%).
Dry rot growth occurs between 0℃ - 26℃ with rapid growth occurring as low as 5℃ and it will die when exposed to temperatures of over 40℃ for even short periods.
The Mycelium (thin strands of hyphae that spread though timbers feeding on starch, sugars and moisture) typically reach beyond what visually appears to be affected timbers.
Dry rot can, on average, be expected to grow around 1meter per year but this will depend on local conditions within the property. If you imagine the roots of a tree spreading through the soil in you garden. Dry rot spreads in a similar way by sending out strands of hyphae into damp timbers.