All wood has the potential for rotting, as it contains a certain amount of moisture. If moisture content is below 20 percent, rot typically isn’t a concern. Anything over this provides a potential breeding ground for fungi, which is what causes wood rot. Moisture is just one thing that fungi need to survive. They also need the following:
Favorable temperatures. Anything in the 40°F to 100°F range will do. Oxygen. A food source. The fungi that attack wood prefer carbohydrates in the form of cellulose and lignin.
Wood is made up of cellulose and lignin, and the other factors are pretty hard to control, so fungi abatement efforts generally focus on the one variable—moisture—that we can do something about.
Dry vs Wet Rot
People used to distinguish between different kinds of wood rot as being dry or wet. This was misleading, as it made it seem like dry wood could develop rot. This simply isn’t possible. All rotten wood is wet wood, or has been wet at one time. We’ll repeat it one more time: Dry wood cannot decay. Still, you’ll hear people call certain types of rot “dryrot.” What they’re really referring to is brown rot, which is one of three types of wood rots. This rot cracks wood against the grain, causing it to split and crumble. In advanced stages of brown rot, after the rot has taken all the nutrients out of the wood, it can also become dry and powdery. The other types of wood rot are
White rots. As the name suggests, these rots cause affected wood to take on a white appearance, which can range from grayish-white to yellowish. In their advanced stages, white rots make wood look stringy and feel spongy or springy. Soft rots. These are rare inside of homes, but they have been known to attack wood shingles in wet climates.
Some rots can grow inside wood for a long time and cause extensive damage before they are detected. Others develop crusts called “fruiting bodies” on the surface of the wood.
Rot vs Mold
Mold (and mildew) are also fungi that spring up around moisture. While they indicate moisture problems and can cause discoloration,they themselves don’t cause wood decay. They can, however, increase wood’s absorption ability, which can make it more prone to fungal growth. Another type of fungi called “sap stain fungi” looks like surface mold. However, it, too, doesn’t weaken wood structures; it only discolors them. Sap stain fungi stops growing when wood dries out. Its presence typically indicates wood that was wet atone time but no longer is.
