Wet lumber, is also called green lumber. It is wood which is used for construction that has a higher level of moisture that that of kiln dried wood for example.
When a tree is felled there tends to be a lot of water in the cells of the wood. The term for water that has accumulated in these cells is ‘free water’. After the tree is cut, the free water starts to slowly evaporate and will only stop this process when the level of moisture in the wood reaches the same level of moisture as its environment. A term used for this process is EMC or equilibrium moisture content.
Why are we talking about a woods evaporation process you might ask? Well, when it comes to green lumber, there has not been enough time for the wood to reach EMC, or the process has been hindered. For example, it is often hindered because it is usually wrapped in plastic before being stored after processing. This means that when the wood is unwrapped for use on a construction site, it still maintains a high-water content level.
States such as Arizona and parts of California which are drier, hotter areas of the country will often use green lumber. This is because the wood will dry out much faster.
One reason that wet lumber is used is that it’s usually a cheaper option. Also, due to it being a softer wood, it is less prone to splitting and easier to drive a nail into.