Decking

The Dirty Details

Chemically Pressure-Treated Wood

Chromium copper arsenate, or CCA, was once widely used as a preservative and insecticide in pressure-treated wood. In 2001, tests by EWG and the Healthy Building Network showed that wood treated with CCA could expose people to dangerous levels of arsenic, spurring the Environmental Protection Agency to force its removal from the market.

Copper-based chemicals replaced the arsenic preservative, but some of them are also hazardous. For example, alkaline copper quaternary and copper azole are extremely toxic to aquatic life and should never be used in areas where runoff can be carried to surface waters, marshes or coastal areas. Borate-based wood preservatives are also common, but they can leach out of wet wood, leaving the wood vulnerable to decay.

Note that chemically-preserved wood is especially dangerous for use in raised garden beds, as the chemicals may leach out and be taken up by plants, including vegetables.

Composite Decking

Composite decking materials combine wood fibers, recycled plastics, fiberglass and preservatives to form wood-like boards that are highly resistant to weathering and decay, and are splinter-free. They require minimal maintenance, although the color can fade over time. While composite decking is made from recycled materials, we do not recommend it as it is not itself recyclable and must be disposed of in a landfill.

Toxic Finishes

Deck stains and finishes may contain carcinogenic toxic solvents that emit volatile organic compounds, or VOCs. Read more about safer options for these products in the guide’s wood stains and finishes section.

Heat-Treated Lumber

Heat-treated wood does not use chemical preservatives, but the heat and steam required for production is energy intensive.

Best Choices

Naturally Weather-Resistant Wood

Some types of wood, including cedar, black locust and Southern cypress, contain oils and tannins that make them naturally resistant to insects and decay. They do not require chemical treatment, but they still need to be waterproofed and stained. Some tropical hardwoods, like ipe and tigerwood, are also naturally resistant, but must be shipped overlong distances and are more expensive than cedar.

It is especially important to choose lumber certified by the FSC. And, if possible, choose FSC-certified wood from local sources to minimize the large carbon footprint that results from shipping wood long distances.

If FSC-certified wood is not available, your next best option is to use locally and sustainably harvested wood with a traceable source. Look for local companies that both harvest and sell the lumber, so you can more easily track the wood’s origin.

Recycled Plastic Planking

Plastic planking made from recycled material is another good option. Look for products made with high post-consumer recycled content that is mostly comprised of HDPE (high-density polyethylene) or LDPE (low-density polyethylene). These products are made from recycled plastics such as milk jugs and grocery bags. Avoid fiberglass-reinforced and PVC plastic materials, as they contain hazardous chemicals.

Plastic planking doesn’t need to be painted, stained or sealed. It’s stain-resistant and won’t crack or splinter. It’s also less toxic than pressure-treated wood preserved with chemicals. But, because it is not as strong as wood, plastic decks can sag under too much weight, and temperature changes can cause the material to expand and contract.

Reclaimed Wood

Using reclaimed or salvaged wood eliminates the need to harvest new trees. Look for wood like cedar or redwood, but take care to learn where your wood came from, as old wood from decks, porches or fence posts is likely to be chemically treated. Note that arsenic-treated wood has a green tint that weathers to gray.

Resources like the Building Materials Reuse Association’s database, CalRecycle in California, Community Forklift in Washington, D.C., or Big Reuse in New York can help you find sources of untreated, reclaimed wood.

Aluminum Decking

Aluminum decking is good choice because it is lighter, stronger and more durable than wood or plastic. It is also waterproof, completely weather and pest-resistant, and 100 percent recyclable, but it can be quite expensive.