Moisture content is the critical factor that makes wood susceptible to decay. It must exceed 28%, and liquid water must be present in cell cavities before decay fungi can gain
… a toehold. Once established, some fungi can carry on their destruction at a moisture content as low as 20%. When moisture content falls below this level, all fungal activity stops. That's one reason why framing lumber is dried to 19% moisture content or less. (MORE)