Thermally Modified Wood: A Healthier Alternative

What is Thermally Modified Wood?

Thermally modified wood is a natural, non-toxic alternative to chemically treated wood products for the home. Unlike pressure-treated lumber, thermally modified wood undergoes a thermal modification process. The wood is essentially "cooked" in oxygen-free ovens at temperatures over 400 degrees Fahrenheit.

What Does Thermally Modifying Wood Do?

The thermal modification process changes the cellular and molecular makeup of wood by removing all organic compounds from the wood cells. So, wood products will no longer be able to absorb water. In turn, this reduces the wood's ability to expand or contract, which is one of the leading causes of water absorption and rot in outdoor uses. This lack of moisture content in the wood means that the wood's cellulose will no longer act as a "food source" for fungi or insects. In essence, the cooking of the wood with high heat creates a naturally durable wood product that will, in theory, be permanently resistant to water, fungus, insects, and decay.

Does Thermal Modification Change the Look of Wood?

From an aesthetic standpoint, thermally modified wood offers some unique benefits and characteristics. The process of treating the wood at a high temperature gives it a natural deep brown hue. This beautiful color negates the need for chemical varnishes or stains, most of which off-gas various volatile organic compounds (VOCs) and require ongoing maintenance. Many homeowners find that the natural dark brown color resembles tropical hardwoods. The use of a sealant to protect the wood from UV rays is often all that is needed to maintain this beautiful natural color.

Where Can I Use Thermally Modified Wood?

The bending strength of the wood is reduced during the heating process. So, thermally modified wood is not suitable for structural applications. It is commonly used for non-load-bearing applications such as decking, siding, flooring, wall paneling, ceilings, accent walls, and even doors (interior and exterior)!

Is Pressure Treated Lumber Toxic?

Much of the lumber used in the building industry today is treated with a wide array of chemicals. These wood preservatives used include:

• Pentachlorophenol (Penta)
• Chromated copper arsenate (CCA)
• Ammoniacal copper arsenate (ACA)
• Fluorochrome arsenate phenol (FCAP)
• Creosote
• Copper sulfate
• Tributyl-tin oxide
• Tetrachlorophenol
• Zinc naphthenates

These chemicals help extend the lifespan and durability of wood by protecting it from bacteria, fungi, and other pests that can cause wood to rot and decompose. However, dozens of health and environmental problems are associated with the use of these chemicals and pesticides.

The Center for Disease Control (CDC) finds that chromated copper arsenate (CCA) can contaminate local soils through leaching. Young children are at a higher risk for consuming CCA, which can accumulate in soils around decks and other outdoor wood structures that have been treated with this product. Arsenic found in CCA has been found to increase the risk of cancer. This risk is incredibly high in children who may be exposed to chemically treated wood in outdoor settings.

In addition, for exterior applications where pressure-treated lumber comes into contact with metal, it can corrode the metal. When working with pressure-treated lumber for exterior projects, be sure to use fasteners that are "hot-dipped" and meet the ASTM A653 standard to ensure that they will last as long as the structure.

What Are the Health and Environmental Benefits of Thermally Modified Wood?

One of the main benefits of thermally modified wood products is that it offers a natural and non-toxic way to preserve wood products without using unhealthy pesticides and fungicides.

As the cooking process removes moisture from the wood, the timber is much more lightweight than regular lumber, making it easier to work with from an installation standpoint. Because it no longer has any water or moisture, the wood is much less susceptible to warping or chipping, making it much more structurally sound. From a durability perspective, thermally modified wood has maximum weather resistance properties. Thermally modified decking can be guaranteed for up to 25 years.

Another added benefit is that you can use a wider variety of tree species. This versatility allows homeowners to make conscientious decisions about sourcing their lumber from local sources. In many cases, fast-growing local forest stands can be thermally modified and subsequently used for lumber for almost every home construction project.

Where to Buy Thermally Modified Wood?

While there are dozens of established companies in Europe producing high-quality thermally modified wood, the carbon emissions associated with shipping lumber across the Atlantic increase the embodied energy of your home. Fortunately, many manufacturers are now producing this type of wood across North America. Below, we review a few of the top manufacturers of thermally modified wood.