Last Updated: Jul 5, 2021
Our article on pressure-treated wood decking covers wood treated with metallic, copper-based formulations rated for ground contact. Copper-based treated lumber has been the dominant formulation since the early 2000s when the United States and Canada phased out copper arsenate (CCA) with several environmental and human health concerns. The newer formulations that eliminate arsenate have been an improvement. But, the utilization of copper still poses problems for its ability to corrode certain types of fasteners and its potential to harm aquatic life via leaching. Care should also be taken with children, and eating off pressure-treated wood is not advised.
The newest preservatives and formulations are nonmetallic, carbon-based formulations that eliminate all metals, including copper. These new formulations are exciting examples of modern technology combining natural products like wood with advanced building science.
This type of lumber is the newest kid on the block in the treated lumber realm. The formulations do not use copper or any metallic-based compound, eliminating the risk of metal leaching over time. Carbon-based treated lumber is only rated for above-ground use. This type of lumber is an excellent option for decking, stairs, fencing, window and door trim, sill plates, porches, arbors, gazebos, trellis, walkways, and outdoor furniture. These formulations have no odor or color, and you can paint or stain them.
The water-based formulations used in this type of lumber replace copper additives with biocides, fungicides, and water repellants that protect termites, fungus, and water damage. The specific fungicides used are propiconazole and tebuconazole with the insecticide being imidacloprid. Makers force the formulations into the wood almost to the center with a pressure vacuum. These chemicals are all EPA registered ingredients, but they still fall into the category of an agricultural pesticide at the end of the day.
The species used for treated lumber is typically wood that is not inherently very durable before treatment. Pine (pinus) is common because it accepts treatments well and is a widespread and abundantly available tree.
Overall, the research points to a lower environmental persistence and toxicity than previous generations of wood preservatives or the current copper-based alternatives. However, this doesn't mean there are no ecological risks to the chemicals used in the formulations.
Wood is a renewable resource that reduces our demand for metals and petroleum products. Industry can sustainably manage forests in a way that preserves and protects water, soil, and wildlife. Treated lumber has reduced the demand for timber harvesting by extending the service life of the wood product. This treatment has saved countless acres from being harvested over the decades and was especially crucial to keeping forests at the turn of the 19th century.
It is well documented that these newer, metallic-free formulations are an improvement from an ecological perspective over copper-based formulations. Research is ongoing on the biocides and their persistence and impacts on the environment. Extensive studies of preservative-treated wood have indicated that environmental pesticide concentrations from most treated wood structures are unlikely to reach levels of concern.
The manufacturers claim the biocides used in the preservative will degrade in soil and are not bioaccumulative. Diving deeper into this, it's not so evident if this is universally true in all environmental conditions. For example, imidacloprid is broken down rapidly by water and sunlight. Still, it can last for months to years in soil depending on the pH and other factors of the surrounding environment. The pesticides used in these formulations deter insects by design, so they are very toxic to these species.
Research has determined that the fungicide propiconazole has a low chance of bioaccumulation. However, the same studies decided it could be moderately persistent and toxic to aquatic environments while persisting in anaerobic conditions. It's essential to keep in mind that these studies were conducted with much larger quantities of pesticides than what one experiences with treated lumber.
The US Environmental Protection Agency (EPA) approved the preservatives used in carbon-based treated lumber after undergoing strict toxicological reviews to identify potential human health or environmental risk. While they are non-toxic to humans in the small quantities used in the lumber and their leaching is minimal, some people might not like using agricultural pesticides. You should always take precautions when dealing with any pesticide. Sealing the wood after installation can further reduce any chance of exposure to these chemicals and reduce their leaching out of the wood.
The insecticide imidacloprid is more toxic to insects than birds and mammals because it binds better to the receptors of insect nerve cells. Imidacloprid does not absorb through the skin easily. The United States Environmental Protection Agency and the International Agency for Research on Cancer have not classified imidacloprid for a potential to cause cancer. Tebuconazole, a fungicide used in wood preservative formulations, has low acute toxicity via oral exposure and moderate toxicity by inhalation. It has been classified as a possible human carcinogen.
Children may be at higher risk of exposure to pesticides because of increased contact with the ground. Their skin is thinner, and their bodies break down chemicals differently.
Ecolife-branded lumber (EL2) lumber and Wolmanized EraWood are both copper-free carbon-based pressure-treated wood options.
Current (May 2021) prices for Ecolife-branded lumber (EL2) lumber from Lowes are USD 8.27 for a 2x4x8. This is higher than usual as prices are currently high due to recent increases in lumber costs.
Some brands have limited lifetime warranty and, if properly maintained, can last 40-50 years. The Eco Life-treated lumber manufacturer says its water repellency lasts for up to 3 years before needing to be re-treated with a water-based water repellent. No maintenance is required to renew resistance to fungi and termites.
Regular woodworking tools can be used with carbon-based treated lumber. When sawing or sanding wood, wear a dust mask, safety glasses, long sleeves, and gloves. Whenever possible, cut lumber outdoors. After working with wood and before eating or drinking, thoroughly wash exposed skin areas. Preservatives and sawdust may accumulate on clothes, so they should be washed before reuse and washed separately from other household clothing. Vacuum or sweep up sawdust from treated lumber and dispose of it in the trash (unlike untreated wood sawdust that could be composted).
Treated lumber can often come with high moisture content. Be mindful of this during installation and alter your wood placement and gaps between boards based on the moisture content. As the wood dries, it shrinks width-wise across the grains. Length along the grain will remain stable during drying, however. A wood moisture meter helps measure the moisture content of the wood.
Unlike copper-based formulations in treated lumber, carbon-based formulations are non-corrosive to metal fasteners. Always be sure to use corrosion-resistant fasteners for exterior use. After cutting lumber, liberally coat cut ends or holes in the wood with a suitable wood preservative product.
You can paint or stain treated lumber any color. Latex and oil-based paints, stains, or water repellent coatings with UV protection are recommended. Make sure that the wood is dry and clean before applying any finish coating. Always follow the manufacturer's recommendations for the proper finishing of treated lumber.
Never use any pressure-treated wood for applications around beehives or where the preservative could become a human or animal food component.
Power washing on low pressure is acceptable for cleaning off treated lumber.
To revitalize a faded appearance caused by dirt, mildew, and mold, use a deck brightener to clean the wood. Reapply paint or stain as needed to maintain the desired finish.
Carbon-based treated lumber that eliminates metals from the formulations is a step in the right direction for treated lumber for above-ground applications. The new compounds still utilize synthetic agricultural pesticides and should be used responsibly. As formulations evolve in response to research and consumer demand, future formulations will only have fewer concerns than the previous, as we have witnessed over the past century of wood preservative evolution. There is still work to create a genuinely non-toxic lumber treatment that limits its impacts in all phases of the wood product's lifecycle.
If you opt to use treated lumber, you might want to take a diverse approach. For ground contact, you'll want to stick with the copper-based formulations. You can use carbon-based treated lumber for above-ground use. Alternatively, you could use a naturally durable wood species and treat the surface yourself with your choice of preservative.
Based in Washington State, Tom's education focuses on holistic land management that sustainably grows renewable building materials in a way that replenishes natural systems. His interest is in building systems that combine old techniques and modern science.