Treated lumber is lumber that has had chemical preservatives pressured or otherwise forced into it. The preservatives help defend the wood against termites, natural deterioration, and other dangers and issues that would naturally effect the lumber.

Classifications of Treatment

There are three broad classifications of treatment: Waterborne, Creosote, and Oil-borne. Waterborne treated wood is usually used for building structures. This includes residential, industrial, and commercial buildings. Creosote treated lumber is primarily used for guardrail posts, railroad ties, and timbers used in marine structures. Oil-borne treated wood is mostly used for utility poles and cross arms. Each of these can be further broken down and categorized, such as varying types of Waterborne treatments having names such as Alkaline Copper Quat, Copper Azole, and more.

Retention Levels

There are varying standard retention levels of the preservatives for use in varying locations. They are generally split between "above ground" and "ground contact" standards, with ground contact being the harsher of the two, therefore having the greater retention. "Ground contact" refers to wood that actually touches the soil.