Know the Difference: Green or Kiln Dried Lumber
"If you've ever purchased lumber and looked at the item descriptions, you'll notice it either says green or kiln dried. Maybe you have an idea of what this means, but perhaps you don't. Either way lets take a closer look at each of these terms. A few of their characteristics may have an effect when considering your next DIY project."
It's been a very dry winter in Seattle, great for crisp morning walks with the dog or getting some work done around the house. (Sorry to the skiers out there. I'll keep my fingers crossed for a late season.) Most probably prefer drier weather rather than wet—it just makes getting things done easier. But what about the moisture in our lumber? Can this affect your DIY project?
Green Lumber
One of the biggest drawbacks to using green lumber is the moisture in wood won't stay there.
Green does not refer to any hue or coloring. In fact, lumber at its basic form is considered green lumber. It's milled to a certain dimension, finished to an extent (e.g. eased edges, rough face, smooth on all sides) and then shipped out for consumers to purchase. Moisture content is usually pretty high. Depending on the species, it can be anywhere from 24%-29%. Next time you are at Dunn Lumber, ask to feel a piece of 2x4 green cedar. It's impressive how much extra weight all that moisture adds!
One of the biggest drawbacks to using green lumber is the moisture in wood won't stay there. As it dries, the wood will tend to crack, warp, and check as the board shrinks. This is especially true in direct sunlight or a heated area without good circulation. Water in the wood also creates a poor surface for products like paint and stain to properly bond, which can lead to many difficulties later.
All that being said, there are some projects where it makes sense to go with a green material. Cedar fence boards are a great example. It's actually an industry standard for cedar fencing to be green. Since the boards are thin (9/16"-5/8"), there is minimal contraction that will occur when drying. The boards also have the added benefit of being vertical, allowing for airflow on all sides.
Kiln Dried
A great example of when to use kiln dried wood, besides the obvious framing lumber, is when you are installing a cedar deck.
Kiln drying is a common industry practice that ensures the lumber you buy is not only straight and free of splits, but remains that way after you finish your project. The process of kiln drying starts after the wood has been cut close to what the finish dimension will be. It is then stacked in layers that allows for air to flow evenly around all four sides inside of a large building (the kiln). Inside the building is an extremely controlled environment—heat, moisture, and airflow are all managed, allowing the entire board to dry evenly. Kiln drying brings the moisture content down to around 10%-16% depending on the wood species and dimensions. Another added benefit (since the wood is heated, usually around 125 degrees): it kills any insects that could be lurking in the wood. It's no wonder why most, if not all framing lumber for houses, is Kiln Dried.
Removing the moisture creates a board that is best described as stable, dry enough that it won't warp or check while acclimating to its new home, but with enough moisture to ensure it is still workable. If outside, the wood may still expand and contract with the seasons, but since it was installed at a stable moisture level that expansion and contraction will have a very minimal effect.
A great example of when to use kiln dried wood, besides the obvious framing lumber, is when you are installing a cedar deck. You should always use kiln dried cedar when installing a deck. Assuming it was installed correctly, you should have fairly consistent spacing for the life of the deck. After putting that last screw in, you're ready for your first coat of whatever finish you desire—although you should probably check the weather first!
DIY Needs
Although some lumber may be traditionally stocked in green or kiln dried, it's important to note just because it is stocked one way doesn't mean you can't order it specific to your job. Take Doug Fir beams for example. Normally stocked green, it can be ordered in kiln dried usually in a day or two. It all just depends on what you are planning to do with the lumber.
A great example of this happened with a DIY customer a few days ago. He came in to purchase some tight knot cedar for his project, which is normally stocked green. After speaking with him we found out he was building some rustic desks for his son and himself. Since he was planning on staining right away, it was suggested he use kiln dried cedar. The difference in price was minimal and the product was brought in the very next day thanks to Dunn's great network of suppliers.
Conclusion
Hopefully you've gained some insight into what these two terms mean, but more importantly, you'll keep the difference in mind when you are planning your next DIY project. It really comes down to what your project is, and what you are planning to do with it when finished.
Every project is a little different. If you're still unsure or have other questions feel free to contact your local Dunn Lumber, or leave a comment below and I'll get back to you ASAP. Thanks for reading, and happy building!
