At what moisture content percentage does decay of common wood framing materials begin?

Decay of common wood framing materials typically begins at a moisture content of around 20%. When wood maintains moisture levels at or above this threshold, it creates an ideal environment for fungi, which are responsible for wood decay, to thrive. Fungi require moisture to grow and reproduce, and as the moisture content of the wood rises above this critical level, the risk of decay significantly increases.

While moisture content levels below 20% can also pose risks under certain conditions, they do not create the same immediate danger for wood decay. At around 15% or lower, wood is generally considered to be in a safe range that minimizes the chance of fungal growth. Therefore, the value of 20% represents the threshold where wood decay processes can actively begin.