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What is Pressure Treated Wood?

By R. Kayne
Updated: May 17, 2024

Pressure treated wood is wood that has undergone a process to make it more durable so that it is not susceptible to water, rot, termites, or fungus. It is used for a variety of applications ranging from outdoor decking to utility poles, from railroad ties to playground equipment. Boat docks, aquarium stands, and indoor pools are a few more examples. This type of wood conserves and extends a valuable renewable resource and it is economical.

To make the wood so long lasting, it is first treated with chemical preservatives, then placed in a cylinder under pressure. The pressure forces the chemicals deep into the wood, which then becomes a barrier against natural enemies like termites and decay. The effectiveness of pressure treated wood has been born out by the U.S. Department of Agriculture Forest Service in more than four decades of field testing. Because of its known efficacy, it is often guaranteed against termite infestation and decay for 40 years.

There are three main types of preservatives used in pressure treated wood: water-born preservatives, creosote, and oil-borne preservatives.

For residential indoor and outdoor use, wood treated with water-born preservatives is ideal. Some water-born preservatives are chromated copper arsenate (CCA), ammoniacal copper zinc arsenate (ACZA) and ammoniacal copper quat (ACQ). This type is also used for many commercial and industrial applications, including traffic signposts and noise barriers.

Some uses for wood treated with creosote preservatives are bridges, guardrails, and docks, while utility poles, crossarms, and indoor pools are a few examples of things made from wood treated with oil-born preservatives.

Pressure treated wood is claimed to be safe in studies conducted by the Environmental Protection Agency (EPA). The chemical preservatives, most notably arsenic, have not been found to leach into soil or water. Laboratory studies independent of the EPA also found no increased risk of cancer among those who work with treated wood on a daily basis.

According to research conducted by the Texas A&M Laboratory along with the Southwest Research Institute, wood treated with water-born or creosote preservatives is even safe to use in the vegetable garden among edibles, such as a trellises for tomatoes or vineyard support for grapes. However, the wood itself should not be consumed by humans or animals, and therefore should not be used where it might inadvertently end up in foodstuffs or feed. For example, a cutting board should not be made of pressure treated wood.

If you are looking to build something that will last, consider the advantages of using pressure treated wood. It is available at most lumberyards and home improvement centers. Just look for a stamp or tag of approval by the American Wood-Preservers Association (AWPA) or the American Lumber Standards Committee (ALSC).

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By cbferguson08 — On Jun 20, 2011

Is treated wood safe to burn? I have been looking into this for a while and cannot find a good reference as to why or why not. I assume there is some risk in releasing arsenic into the air and being directly inhaled.

By anon92848 — On Jun 30, 2010

I moved a house onto my existing basement and the under side of the house has green treated plywood. Do I have to do anything to the treated plywood or is it safe to leave it alone? The basement is going to be a living space.

By anon91385 — On Jun 21, 2010

Renee1116: no they will not, since pressure treated has chemicals in it.

By anon63230 — On Jan 31, 2010

We are planning to build a raised garden. The local home improvement store said new pressure treated wood is safe to use, and does not leach arsenic or other toxins. The sales associate did not know what the new preservative was but assured us it was safe. Is this true?

By anon16982 — On Aug 19, 2008

I'd suggest you ask someone at a local lumberyard, since porcupines appear to be a problem in your region.

By Renee1116 — On Aug 18, 2008

Porcupines eat plywood. Will they eat pressure treated plywood?

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