What is pressure-treated wood?
Many of you have used it before. If not, you probably stood on it in some capacity. It’s most commonly used in decks or in certain parts of the walls that are in your house. It withstands the test of time but costs a little more than regular white wood.
But what exactly is it?
Pressure-treated wood goes by a few names: treated lumber, wolmanized lumber, green-treated lumber, or simply “green”. To put it simply, it’s wood that is chemically treated to withstand moisture.
To go a little deeper, pressure-treated lumber is wood that has been immersed in a liquid preservative and placed in a pressure chamber. The chamber forces the chemical into the wood fibers. The pressurized approach makes sure that the chemical makes it to the core of each piece of wood. The process is much more effective than simply soaking the wood in the chemical.
According to the USDA Forest Service, the most common chemical used to treat lumber used to be chromated copper arsenate, or CCA. In 2003, however, the Environmental Protection Agency restricted the use of CCA in residential settings due to health and environmental concerns about arsenic leaching out of the wood. The most widely used alternative to CCA is alkaline copper quat, or ACQ. Copper is toxic to various insects and fungi that might cause decay. ACQ binds to wood fibers very well and allows wood to last decades even when it is in contact with the ground.
The protection provided by the chemical depends on the amount of chemical that the wood absorbs. In the United States, the amount of chemical is measured in pounds of chemical per cubic foot of wood. For ground contact, 0.40 pounds per cubic foot is needed. For foundations, 0.60 pounds per cubic foot is the standard.
The chemicals in treated wood are generally not good for humans. This is why you see warnings advising you to wear gloves, avoid breathing the sawdust, and refrain from burning treated wood.
So where is pressure-treated wood used?
Pressure-treated wood is used on most outdoor projects since it resists moisture that would otherwise have a harmful effect on regular lumber. One of the most common place you see pressure-treated lumber is on decks. Some deck boards are made with pressure-treated lumber, though composite boards have started to replace the PT deck boards. But underneath the deck boards, you’ll often find that all of the material is pressure-treated.
Another common spot to find pressure-treated lumber is on the sill plates of your walls. These plates come in contact with the concrete and thus have to be pressure-treated per building code.