Information Sheet on Pressure Treated Timbers (treated pine)

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. Pressure treated wood 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. Pressure treated wood conserves and extends a valuable renewable resource and it is economical.

To find the most suitable treated timber for your job just enter your project (eg: deck, roof, pergola) in the box below and click the search button.

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, pressure treated wood 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). Water-born pressure treated wood 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 noteably 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 pressure 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, for example as a trellises for tomatoes or vineyard support for grapes. However, pressure treated wood 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.



Treated pine vs. cedar

The Wood Doctor offers his prognosis for outdoor projects using cedar and treated pine. 1998. by Professor Gene Wengert

Q.Help! I have been told, by supposed “experts”–fencing companies–that pressured pine is better than #2 Welco cedar, and that #2 Welco cedar is better than pressured pine! I’ve been told that cedar will not hold up for more than 5 years (if we are lucky). That cedar runners, and not pressured pine runners should be used with cedar. This is an expensive project, and I really do not want to make a mistake. Is there a non-biased opinion comparing the two woods? Or is there a third wood that’s better than all the rest?

A.Properly treated southern pine lumber or posts will last for a hundred years even when in contact with the wet soil. (For above ground use, the amount of preservative required is 0.25 pounds per cubic foot. For ground contact the amount of preservative is increased to 0.40 pounds per cubic foot.

In all cases, make sure that the treating is certified with a stamp or label from the AWPB; this assures you the quality that you need. Never purchase wood without the quality label; never purchase wood that is “treated to refusal” or without the quality assurance stamp or label; there are some people who don’t treat wood well (money is more important than quality.)

The heartwood of western red cedar and Alaska cedar are known to be very decay (and insect) resistant and will also last for a long time. However, the sapwood of cedar (white in color and the second growth cedar (often lighter red than normal) do not seem to possess the same level of decay resistance as the heartwood of old growth. Much of the wood in the stores today contains some sapwood, which will decay within a year or two.

I just put in a deck and used treated pine. The builder wanted to use cedar, but my feeling was that pine would be better for me. Another concern might be that by using old growth cedar we might be doing more damage to the environment than by harvesting the faster growing, more replaceable, pine. I did put in a cedar fence, however, with treated pine posts. I think the cedar has a better look as it ages, but will need occasional checking for weathering damage as the fence ages because fence boards are usually not the highest quality wood to begin with.

Also, even though the chemicals we use for treating are not entirely without environmental risk (we use copper and chromium), the fact that the wood will last for 20 times longer than untreated seems to justify their use (this is referred to as life cycle analysis). It would seem better to cut a tree once every 100 years and use the chemicals rather than to cut a tree every 5 years. Of course, this doesn’t address the issue of whether I need a deck!

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison



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