Wood Decay Conditions

If wood is not pressure treated against decay, then it must be ventilated to keep its moisture content low. Here's why:

The organisms that actually do the work of decay are ever-present in the air and on the surface of the wood. They generally can survive at temperatures between 45 and 110 degrees Fahrenheit. Once the moisture content of the wood rises above 20% (which could be determined with moisture meter), these organisms go into action. Pressure treating effectively makes the wood toxic/poisonous to these little creatures.

So, if the wood may be getting damp and staying damp, make sure it is pressure treated. Most people know that PT lumber is available because that's what decks are made of. Less well known is the fact that pressure treated plywood is also available.