Thermally Modified Wood: A Green Substitute for Pressure-Treated Lumber

You're probably aware that pressure-treated lumber contains known carcinogens and is poisonous to humans and animals. However, it is also 30 to 40 percent less expensive than redwood and lasts twice as long, making it an attractive option for homeowners. Thermally modified wood seeks to bridge the gap between pressure-treated lumber and untreated wood. Instead of using chemicals, thermally modified wood uses heat to improve stability and decay resistance.

Thermally modified wood is treated using heat, not chemicals or metals. The special heating process permanently modifies the wood sugars in the lumber, making it indigestible to insects that eat other types of untreated lumber. In most cases, insects do not recognize thermally treated lumber as being suitable for laying eggs. This type of modified wood also does not support the growth of fungus or mold as well as untreated wood.

People familiar with European building may be aware that thermally modified wood has been used for over 15 years. However, in the United States, it is still relatively uncommon. People who examine a piece of thermally modified lumber may be surprised to find that it is darker than traditional wood. This type of lumber also weighs less than untreated lumber.

Thermally treated wood is also less permeable to water than untreated lumber. The heat treatment used on the lumber also reduces the chance of the wood cupping or warping by reducing moisture levels. However, the moisture levels will be affected by overall humidity levels.

Thermally modified wood is greener than pressure-treated lumber because it avoids carcinogens and disposable is easy. There are also few health concerns when the lumber is being used. Some companies that sell thermally modified lumber use certified sources, making it even more appealing to environmentally conscious home builders.

Thermally modified wood is less dense than untreated lumber, but it is also less strong than untreated lumber. Although the strength-to-weight ratio is barely impacted, the lower density (and therefore lower weight) translates into some strength losses. Builders that want to use thermally modified lumber should be sure that the lumber is still appropriately sized for the job.