Greenwood is unseasoned wood with high moisture content, which can be softer and easier to work with but prone to warping and poor performance in fires. Drying allows wood to remain straight and smooth, and seasoned wood should be used for fires. Balancing moisture content is important when purchasing lumber.
Greenwood is wood that has not been treated or seasoned, maintaining a high moisture content. Typically, wood is considered green when it has been recently harvested and when the moisture content is between 25 and 30%, depending on the tree. There are a number of characteristics associated with unseasoned wood that are important to consider when making a choice between green and seasoned wood.
When trees are alive, they have a high moisture content, thanks to their extensive vascular systems, which transmit water and nutrients throughout the tree. Once a tree is felled, circulation stops, but the wood remains very moist for months or even years, depending on the climate, unless the wood is dried. In warm regions, the wood may be air-dried, and in other areas it may be kiln-dried, for better control of the drying process. Some sawmills process their raw lumber into lumber for kilning, while others dry whole logs.
Wood that has not yet undergone the drying process is known as greenwood. This type of wood is much softer than seasoned wood and less prone to splitting. Some people prefer to work with green wood, because it’s much more forgiving and isn’t as hard on tools as seasoned wood. However, there are some disadvantages to using wood that hasn’t been seasoned yet.
The main problem with green wood is that as the wood dries out, it shrinks and warps. If unseasoned wood is used in something like a structure, it will warp as it shrinks, potentially causing structural instability or reducing the airtight nature of the structure. Drying allows this process to occur before the wood is used, ensuring the wood remains straight and smooth when used in projects. Greenwood is also easy to carve or otherwise damage, creating undesirable structural or aesthetic defects.
This type of wood also performs very poorly in fires, due to the high moisture content. It burns inefficiently and often not very cleanly, generating lots of smoke and debris that will clog the chimney. Green wood should be avoided when building fires, and ideally dense seasoned woods such as oak and madrone should be used, as they burn very efficiently and generate a lot of heat.
Some lumberyards carry green wood for their customers, while others have to special order it. You can purchase green wood and season it at home or in the shop, although many people prefer to leave this process up to the lumber company. Seasoned wood will also need to be able to adapt to the climate it will be used in, which is an important consideration when purchasing a load of lumber for a project. The goal is to balance the moisture content of the wood with the moisture content of the air, reducing the amount of moisture that can be absorbed by the wood and therefore minimizing the amount of swelling and subsequent warping and shrinkage of the wood.
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