Contrary to popular usage, dry rot does not mean rot that can happen in dry wood, or wood that has rotted and dried out. Dry rot is a specific kind of fungus, although the term is very commonly misused to describe all wood rot. This is unfortunate, because it disassociates rot from moisture. Wood rot always requires moisture, and the key to wood durability is the control of moisture. Wood that rotted long ago and is now dry was moist at the time of the rot. The true dry rot fungus has the ability to tap into a water source and conduct water to what would otherwise be dry wood. However, it has to wet the wood before it can attack the wood. The true dry rot fungus is more likely to be found in buildings that contain brick or stone than in all-wood buildings.
HOW FAST DOES WOOD DECAY?
It’s impossible to say – there are so many variables that influence the process. In a laboratory, under ideal conditions for decay fungi, wood can rot quite quickly. However, in real life applications, the entire process is slower and unpredictable
From: Canadian Wood Council
CONDITIONS NECESSARY FOR THE DECAY OF WOOD
Four conditions are necessary for the development of wood decay producing fungi. Eliminate any one of these and decay fungi cannot survive.
An adequate supply of oxygen
A favorable temperature (32° - 90°F)
Moisture in excess of the fiber saturation point (> 25-30%)
A suitable source of energy and nutrients (i.e. the wood)
The amount of oxygen surrounding wood and the atmospheric temperature are quite difficult to control in wood in service. Moisture content, on the other hand, can be regulated in wood which is not likely to be exposed to liquid water or to extremely high humidities following drying. If wood is maintained at 20-25% MC it will not rot. Therefore, wood used indoors for most uses need only be dried to provide long-term protection from rot.
From: The U of Minnisota, Forest Products development Unit
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