Trees are approximately one-third water, the moisture content of freshly cut lumber. Over time, the wood air dries to 5-10%. The boardwalk woods may be slightly higher or lower in moisture content depending on the climate – rain, relative humidity, etc. For re-use, the woods need to be milled and dried (air or kiln), and arrive at a job site at under 10% or 12% for exterior applications. Water is always present in some percentage, contributing to the expansion and contraction of the woods over time.