Pressure Treated Decking: It Has Come a Long Way

By Tom Saxton, Rise Writer

Last Updated: Jul 2, 2021

Pressure-treated lumber has generally gotten a bad reputation for its toxic chemicals, notably arsenic and chromium. However, in the early 2000s, copper arsenate (CCA) treatment was phased out for residential use across North America, and new, potentially less toxic substitutes filled in the niche. As we learn more about the toxicity of various chemicals, our science advances to discover safer alternatives. Treated lumber has been a beneficiary of modern science, finding less toxic options. However, there's still progress needed to create a genuinely non-toxic and sustainable lumber treatment. This article focuses on the most common pressure-treated systems that use copper as the main ingredient.

What Is Pressure Treated Decking?

Pressure-treated wood decking is different from untreated wood decking due to increased resistance to moisture, rot, fungal decay, insects, and physical damage. Untreated wood is treated with pressure and vacuum technology that forces preservatives deep into the wood grains during the manufacturing process. Pressure-treated lumber is labeled with the type of chemicals it was treated with and whether it is rated for ground contact or used above ground.

This article focuses on copper-based preservatives that result in lumber rated for ground contact applications. Our article on non-metallic treated wood covers lumber rated for above-ground use.

What Is Pressure Treated Decking Made Of?

Treated wood decking is typically composed of pine, spruce, or fir lumber. These species are not naturally rot-resistant but are abundant and locally available species. The lumber is then treated with different chemicals, most commonly ammonia copper quaternary (ACQ). Other treatments are copper azole (CA), micronized copper quaternary (MCQ), and micronized copper azole (MCA). The micronized versions are newer advancements that reduce corrosion potential to fasteners. Still, studies are ongoing on using these nano-sized copper particles and their environmental impacts.

ACQ is a water-based treatment that contains no arsenic or chromium and can be used in above-ground or ground-contact applications. ACQ is approved by the American Wood Protection Association (formerly the American Wood Preservers' Association).

Is Pressure Treated Decking Environmentally Friendly?

It's pretty challenging to find a universal answer to this regarding any decking material. There are pros and cons to each of them. For treated wood decking, it depends on the type of chemical treatment, where and how the wood is harvested, and how far that wood had to travel to get to you.

Wood Harvesting Considerations

On the lumber front, wood is a renewable resource that reduces our demand for metals and petroleum products. Wood is the only renewable resource available for decking. There is a perception that cutting trees is always a bad thing, but we need wood products. If we stop domestic production of wood products, they will be outsourced to developing countries. Often, these countries have not yet implemented any strict environmental or social regulations. From a global perspective, it is likely best to source lumber and manages forests domestically and responsibly rather than outsource these materials. However, wood is not always sustainably sourced; it's a dynamic material in which harvesting is quite complex. Some wood can come from unsustainably managed forests where they clear-cut large swaths of land. Other wood could be coming from old-growth forests that are multiple centuries old or from boreal forests or tropical forests where regeneration is difficult. Thankfully, there are certifications such as Forest Stewardship Council (FSC), Sustainable Forestry Initiative Program (SFI), Canadian Standards Association (CSA) that set rigorous standards for sustainable forest management. We discuss these and others in our Rise Guide to Wood Certification Programs and Sustainable Forestry.

Chemical Considerations

On the chemical front, ACQ is a big step up over CCA primarily because it eliminates arsenic. The EPA claims that replacing CCA with ACQ was one of the most dramatic pollution prevention advancements in recent history. However, because of the toxicity of copper to aquatic organisms and ACQ may leach more copper than CCA, it is not recommended for applications near marine ecosystems. It is recommended to seal the lumber once a year to reduce leaching. During manufacturing, ACQ generates more air pollution than CCA did, mainly in the form of ammonia.

Copper mining is necessary to create pressure-treated lumber, and its negative environmental and human health impacts are well documented. On the other hand, treated lumber reduces the number of cut down trees because it increases their service life.

Is Pressure Treated Decking Healthy?

Based on its use of copper oxide and quaternary ammonium, ACQ is a relatively low risk to human health in the average level of exposure we have with it after installation. Further research on ACQ chemicals' components determined no acute or chronic adverse effects on adults or children in contact with ACQ-treated lumber. The main concern is during cutting and the sawdust that comes with it. Users should ensure that they take precautionary measures and wear gloves, safety glasses, and a mask when cutting and handling the lumber.

While the research shows low risk for adverse effects on adults and children, no precaution level for young children is too great. So it is still recommended to be mindful of children crawling on treated lumber decks and subsequent hand-to-mouth behaviors.

Manufacturers recommend that you seal the lumber after installation. If pressure-treated wood decking has not been sealed, you should avoid walking on it barefoot.

How Much Is Pressure Treated Decking?

Treated lumber decking is typically the most affordable decking option for initial installation. The cost per square foot is generally between $5.75 and $12.50. There is an added cost of annual resealing that is recommended you should take into account. Manufacturers marked ACQ under brand names Preserve®, Preserve Plus®, NatureWood® by Osmose, ProGuard™, and Wolmanized Natural Select by Arch Treatment.

How Long Does Pressure Treated Decking Last?

If you maintain your pressure-treated deck, it can last 50 years. A roof over the deck will allow it to last much longer. A trick to increasing the lifespan of any wood deck is to increase the distance from the ground. By keeping ample space between the deck and the ground, the wood will absorb less moisture from the soil and dry out quicker.

How to Cut Pressure Treated Decking?

You can cut treated lumber with any standard wood cutting tools. Sawdust is the primary source of health concerns with handling treated lumber, so always wear a dust mask, goggles, and gloves when cutting and handling the wood. You should also wash the clothes you wear while cutting the lumber separately from other clothing before use. Always wash exposed areas of your skin after cutting the materials, as dust can settle on you.

What Are Some Tips for Installing Pressure Treated Decking?

Treated lumber is often wet when it is purchased. Install boards butted up to adjacent boards tightly, and then when the wood dries, gaps will form in between the boards to allow for water drainage. This process is different from that of untreated lumber used for decks. You would install the boards with a gap between them in those cases since they are usually already kiln or air-dried.
To help resist warping as the boards dry, position boards with the end grain shape an arch so that the arch's center is pointing away from adjoining lumber.
Pressure-treated wood can corrode fasteners. You must ensure your fasteners are labeled as acceptable for use with the type of treated lumber you are using. These are typically 304 or 316 stainless steel fasteners, hot-dipped galvanized fasteners with at least a G-185 designation, and fasteners with ceramic coatings. Regularly inspect fasteners for signs of corrosion or loosening. Corrosion will appear red or rust-colored; any white discoloration is normal and acceptable.
Remember to predrill holes in lumber to reduce the chance of the grains splitting, especially if you are drilling close to the end of the board. Be sure to place as least one screw through the center of each board's end to help minimize bowing upward as the boards dry.
Some decks are built with pressure-treated lumber for beams, posts, and joists due to increased durability and strength but use untreated lumber or composite decking for the platform. Some local building codes do not allow any posts, even treated lumber, to be buried in the soil. You'll require concrete footings in these cases, which is a best practice regardless of your local codes.
Within six weeks of finishing the deck, seal the wood and reapply the sealant annually.

How to Clean Pressure Treated Decking?

Power washing on low pressure is acceptable to cleaning off decks. It would be best if you did this before the annual touch-up of the sealant.

How to Restore Faded Pressure Treated Decking?

Treated lumber should be resealed once a year. You should stain every two to three years. If you chose to paint instead of applying a stain, repaint as necessary.

Is Any Pressure Treated Wood Made Without Metals?

Newer formulations of wood treatment are eliminating metals like copper from the ingredients list. These recent advancements are exciting developments to improving the sustainability of treated lumber by reducing the potential for leaching of metals from the lumber over time. These brands are EL2 (sold as Ecolife-branded lumber) and PTI (sold as Wolmanized EraWood).

What Are The Benefits of Pressure Treated Decking?

Renewable Resource – Wood is a renewable resource that can be regrown with holistic, sustainable forest management that focuses on the health and condition of the soil, wildlife, and water.
Durable - Pressure treated wood very durable and resists scratches, dents, and water damage. Pressure treated wood has a long lifespan of 40-50 years with proper maintenance. It is also easy and affordable to repair if it is damaged.
Insect resistance -Treated with chemicals that deter insects, pressure treated wood reduces the chances of structural damage from species such as termites or beetles.
Affordable - Pressure treated wood is typically the most affordable type of decking material for initial installation.

What Are The Drawbacks of Pressure Treated Decking?

Extraction and Manufacturing – Environmentally damaging copper mining is necessary to creating the chemical treatment on the wood. During the next step, the chemical treatments' manufacturing releases particulates into the air, such as ammonia. Forests aren't always harvested sustainably. These less than ideal practicces can negatively impact forest ecosystems' health, condition, and resiliency.
Chemical concerns- Pressure treated wood is treated with synthetic chemicals. It can be hazardous if not handled correctly during cutting. Copper can leach from the lumber into nearby soils and waterways. Treated lumber releases toxic chemicals when burned.
Green and wet when purchased- Treated lumber is often still wet when you buy it. Lumber does all of its warping while drying, so you need to inspect pieces of defects when purchasing thoroughly. Pressure treated wood is typically wood of the lowest quality, so it can check and warp faster than other wood types.
High-maintenance- Pressure treated wood requires annual sealing to reduce splintering, fading, checking, and leaching chemical treatment. Wood can fade with exposure to UV and retain stains from leaves if not cleaned off.
Splinters- Wood will splinter with time. Sealants can reduce this occurrence.
Disposal - Treated lumber should be disposed of in a landfill, similar to composite decking, and sawdust should not be composted or used as mulch. You can potentially take it to a recycling center that handles this type of product, but that could prove challenging to find locally. You should never burn treated lumber as a means of disposal.

Treated wood decking is an affordable decking option with a variety of advantages and disadvantages. If forests are managed holistically, wood products are among the most sustainable and renewable building materials available. Despite this, there are warranted concerns about the chemicals used in pressure treated wood, the mining and manufacturing necessary to creating these chemicals, and their debated toxicity to humans and aquatic life.

If you choose to build a wood deck, whenever possible and appropriate, use locally sourced and naturally durable, untreated wood, particularly in areas of the deck where people or animals will come into contact with wood or in areas near water. Inherently durable species are western red cedar, redwood, and douglas fir, western larch in western North America, white oak, eastern red cedar, northern white cedar, black locust, and catalpa in eastern North America. You can surface seal untreated wood decking with non-toxic products such as Vermont Natural Coatings' Penetrating Water Proofer.

To learn more about various types of decking, check out more of our decking articles:

Disclaimer: This article does not constitute a product endorsement however Rise does reserve the right to recommend relevant products based on the articles content to provide a more comprehensive experience for the reader.Last Modified: 2021-07-02T17:29:37+0000

Article by:

Tom Saxton

Based in Washington State, Tom's education focuses on holistic land management that sustainably grows renewable building materials in a way that replenishes natural systems. His interest is in building systems that combine old techniques and modern science.