What Is Kiln-Dried Lumber?
Kiln-dried lumber is a type of lumber commonly used in many homes. To understand what it is, you first have to know about a device called a kiln. A kiln is just a type of oven used for things like wood and pottery. It is a mostly-closed oven, but it allows some air to escape. A kiln will usually run at a fairly low temperature. If it didn’t do this, there would be a risk of burning the lumber.
A tree, of course, is the source of all lumber. Like any living organism, its body contains a large amount of water. You wouldn’t want to remove every bit of this internal moisture, because then, it would become brittle. Wood must be able to bend instead of break, at least to a certain extent. That’s why most lumber is only dried out until it has a moisture content of 13-19%. In general, wood is heated at a temperature of 125 degrees, and the sapwood will dry out long before the heartwood.
How Much Water Is Present In A Tree?
You might be surprised at how much moisture a tree contains. According to this study, the number hovers between 47% and 60%. That means the average tree is roughly half water! Of course, geographic location and tree age play a role here.
Since a tree contains so much water, it will shrink as it dries. It won’t lose a full half of its mass, but it will get smaller. As the wood contracts, it can very easily crack. That’s why you should never use green wood to build a house. Kiln-dried lumber has already gone through that process in a controlled environment.
Why Use Kiln-Dried Lumber?
There is one reason above all for which people choose to use kiln-dried lumber. This kind of wood is much more resistant to warping. If you want to understand this fact, you have to know how wood is shaped by heat and pressure. When wood is wet, it becomes a little bit more flexible. Once it dries, it will then become as hard and stiff as ever. People use this fact as a way to shape wood for various projects. By using hot steam, they render the wood into a more flexible form.
Once the wood has been steamed, they put it into a press that holds the wood in the desired shape. Once it dries, it will retain that shape. This process is how they make all kinds of items from wooden wheels to furniture to bows and arrows. Some people use an apparatus called a steam box to bend wood with a mixture of heat and pressure.
A similar process happens when you use lumber to support your home. The weight of the roof and the house itself put pressure on the wood. If it is too moist, it will bend with the pressure. When it dries out with the weather, it will retain the bend. Over time, this will get worse and worse until the lumber finally cracks or becomes too warped to fix. Kiln-dried lumber might still flex a little bit because it retains some moisture; however, it should not flex enough to cause a serious problem.
Will The Wood Stay Dry?
After your kiln-dried lumber has been installed, it will not necessarily remain at the same low moisture content forever. Wood, like many other substances, tends to draw moisture from the air. This quality is called hygroscopicity, and it will play a significant role in the long-term moisture content of the wood. Like any hygroscopic substance, wood will eventually reach equilibrium with the surrounding environment. So, if your environment has 39% humidity, your wood will eventually reach that level.
Using A Wood Moisture Meter
When buying large amounts of wood, it isn’t a bad idea to check the moisture content. A hand-held moisture meter isn’t particularly expensive nor particularly difficult to use. In most cases, these devices have two little prongs that use an electrical charge to find the moisture content of the wood. It does this by detecting the differences in electrical resistance between wood and water. These devices are usually quite easy to use. You just set the meter for the species of wood that you are using, push the two prongs into the surface of the wood, and press a button.
If you are wondering whether or not you need kiln-dried lumber, the answer is probably yes. For all home-building applications, dried wood is superior to “green” wood. It will be far less likely to split, crack, or bend under the immense weight of your home. The only real alternative is air-dried lumber, and it takes much longer to process. If you have found this article to be helpful, we invite you to fill out the contact form below so that we can continue to keep you well-informed.