Whether it’s a deck, a fence, a wall or a horseshoe pit, when you’re building with wood outdoors or in any area where lumber might be in contact with moisture or insects, you want to use a product that’s going to last. For the majority of applications, pressure-treated lumber is the right choice.

Pressure-treated lumber is simply lumber that has been treated with a chemical to make it resistant to insects and fungus. In the pressure-treating process, dry sawn lumber made from woods such as Douglas fir, Hem-Fir, and many species of pine is loaded onto trams and moved into huge cylindrical tanks. A vacuum removes air from the tanks, then a liquid preservative is pumped in and high pressure is then used within the tank to force the liquid deep into the wood’s cells. Some harder species of wood, such as Douglas fir, may be “incised” first — a process of creating short, narrow slits in the wood that increases the penetration of the preservative.

Until fairly recently, chromated copper arsenate (CCA) was the material of choice for pressure treating lumber. However, there were concerns about the arsenic in the wood leaching into the surrounding soil, so in 2004 the EPA and the wood preserving industry jointly agreed to change the chemicals being used in the process. Today, the pressure-treated lumber and plywood available in local lumberyards is typically made with copper azole (CA-B), or with alkaline copper quaternary (ACQ).


Since CCA was relatively inexpensive, most pressure-treated lumber received a high quantity of preservative and was rated for ground contact. Both CA-B and ACQ compounds utilize a lot more copper than was used with the CCA-treated lumber, and since copper prices have risen dramatically in recent years, so has the price of pressure-treated lumber.

To offset that to some degree, pressure-treated lumber with different levels of protection is more readily available than it used to be. Above-ground lumber has less chemical protection and is therefore less expensive than ground contact-rated lumber. For higher levels of protection you can opt for wood that is rated for permanent wood foundations and even salt-water contact. Each piece of lumber will carry a tag or an imprint showing the treatment material and the rating level, or ask the salesperson at the lumberyard to help you with choosing the right one for your application.

The change in treatment chemicals has also necessitated some changes in fasteners and flashings. Because high levels of copper are corrosive to steel, you should avoid standard nails and screws. Instead, utilize hot-dipped galvanized or stainless steel nails, screws and bolts. Flashings should also be galvanized, as well as hangers and other metal connectors.

Aluminum is another material that should not be in direct contact with treated lumber. If you are using aluminum, utilize a material such as heavy plastic sheeting, roofing felt, rubber, or other material to create a barrier between the aluminum and the pressure-treated wood.


Anyone who has worked with pressure-treated materials probably already knows that there are some common-sense precautions that need to be taken. These include:

  • Don’t use pressure-treated wood for cutting boards, counter tops, containers for human or animal food, or other structures in direct contact with food or drinking water.

  • Don’t use sawdust or wood shavings from pressure-treated wood for applications such as animal bedding or garden mulch.

  • Pressure-treated wood scraps should be disposed of with normal household trash. DO NOT burn it in your fireplace, wood stove, or outdoor burn pile, as the fumes and smoke can be toxic.

  • When cutting, drilling, sanding or otherwise working with pressure-treated lumber, wear goggles to protect your eyes and gloves to protect your hands. Be sure to wash your hands thoroughly before eating, smoking or using the toilet.

  • Wash your sawdust-containing work clothes before wearing them again, and wash them separately from the regular laundry.


For complete information on pressure-treated lumber safety precautions, request a Material Safety Data Sheet (MSDS) from the lumberyard when you buy your material.

Remodeling and repair questions? E-mail Paul at paul2887@ykwc.net.

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