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Knocking on wood

On July 1, a 12’ x 5-1/2” wide wood plastic composite (WPC) board on The Home Depot website ran for $26.97. A 2x6-12 of No. 1 pressure-treated, red-dyed softwood was $10.27. The same board in “construction grade” redwood (it looked like No. 2 common) was $16.35 that day.

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The dimensional thickness of the WPC board (the brand was Veranda ArmorGuard) was only 0.93”, so a comparison in board feet seems less appropriate than looking at the square feet of coverage. All three boards provided 5-1/2 sq. ft. of decking.

At, the story that day was fairly similar. Its ChoiceDek Foundations WPC product was priced at $25.81 for a 12’ board.

So, at the end of this exhaustive, incredibly scientific study, we are left with the conclusion that composite decking costs almost twice the price of treated or redwood deck boards. Based on price alone, it would seem the choice is obvious.

And, of course, it isn’t.


On the website, there is a list of more than 100 manufacturers of composite deck boards and the site reviews 55 of their products. It would seem that a woodshop has a huge array of choices when it comes to wood/plastic composites.

These products all have a few facets in common. The first of these is conformity: unlike natural products, there is very little difference between boards in a batch. There is no wane, twist, warp, splitting, knots, checks or rot. That obviously reduces the amount of direct waste on a job site, but it also has a couple of more subtle effects. The first of these is time: the installer doesn’t have to take a minute to check each board for straightness or find the crown when installing it or straighten it mechanically before nailing it down. He/she doesn’t have to work around imperfections, so a stop on the miter saw works the same on every cut (there’s no moving things a couple of inches to avoid a loose knot and then having to remeasure). Those wonderful straight edges also mean that spacers can be used more effectively with composites: one doesn’t have to constantly check the spacing along the length of each board as it is being secured.

Another subtle time saver is the fact that, on many jobs, there’s no need to revisit the lumberyard. With natural boards, one needs to factor in a percentage of waste and then return the unused boards at the end of the job. With the predictability of composites, estimating can be a lot more accurate.

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WPC composites have only been widely available for a couple of decades and most of the plastic-based options being offered today are significantly younger than that. The obvious conclusion here is that warranties, promises and predictions about longevity are based on scientific data and research, rather than on actual field tests. We know that plastics take a long time to decompose, but most composite materials are about half natural fibers (sawdust, bamboo etc.) and, while the manufacturers believe they are fairly invulnerable to Mother Nature’s wrath, that old lady has a habit of surprising us. While WPCs have definitely done well so far, it’s still early. Will the wood fail before the plastic?

Of course, pressure-treated lumber has had some issues, too. Early on, boards were treated with CCA (chromate copper arsenate). At the end of 2003, that compound was replaced with higher levels of copper-based pesticide for products that could be used in residential construction, such as decks, swing sets and landscaping. So, the pressure-treated boards we use today (alkaline copper quaternary, or ACQ) have even less history in the field than the earliest WPCs.

Untreated deck boards such as redwood, cedar, cypress and the like have a long history of being used outdoors. Unlike WPCs, uniformity is not their strength. For example, there’s a great deal of difference between all-heart, construction-heart and No. 2 redwood grades and their longevity is pretty much tied to the quality of the cut. In general, if you pay more, it’ll last longer. That might be especially true when it comes to imports: there is some anecdotal opinion that ipè or mahogany will outlast domestic softwoods.

Maintenance is a huge factor in determining how long a natural, untreated wood board will last outdoors. Regular coating with waterproofing products has a significant impact. Location is also a vital determining factor: a board under a downspout will rot faster than one under an eave and a deck on the north side of a hose will generally outlast one in direct sunlight.

Environmental impact

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A large part of the argument used in marketing literature for both wood composites and untreated natural wood decking is that these products are “green.” On the surface, that might indeed be true. But dig a little deeper and there are definitely some issues worth examining.

A certain very popular Japanese hybrid passenger car can manage about 50 miles on a gallon of gas, which would suggest that it is one of the best environmentally conscious choices one could make. But hidden in its price tag (about $27,000 on average) is the fact that the factory had to build two power systems for each car, one electric and one gas, and those manufacturing processes have some environmental impact. Each car also has a bank of batteries on board, so there is definitely room for debate on whether the entire life cycle of the car, including the production phase, is actually as environmentally friendly as its owners often claim. A very basic small car from most of the major manufacturers will run on a manual four-cylinder and get somewhere in the mid-30s for gas mileage — and it will cost about half the retail price of that popular hybrid. Over the life of the two cars, the gas bill combined with the initial cost (plus interest on a bank loan) can make the decision quite blurred.

WPC products cost more than natural wood, in large part because of the manufacturing process. Yes, they use recycled wood and plastic waste and put it to good use. However, two thoughts come to mind. What is the environmental impact of that manufacturing process: are there emissions from chemical or thermal processes? And when the deck is dismantled, perhaps because the structure to which it is attached fails before it does, how biodegradable is a composite in a landfill compared to a wood board?

Treated lumber also begs some environmental questioning. The very nature of infusing fibrous wood products with copper-based pesticides leaves one wondering if there is a long-term price to pay. Think of the millions of decks, docks and other structures that are washed with rain or snow melt that eventually flows into streams, lakes, aquifers and other groundwater sources. Another minor concern is pointed out on the website of the International Association of Certified Home Inspectors, which states that “ACQ lumber includes copper, which can corrode when it comes in contact with common aluminum building nails.”

Nothing is simple, is it? Even all-natural boards can have a huge environmental impact. The machinery used to harvest and transport logs or to mill, dry, and eventually deliver dimensioned boards to retail outlets all runs on some form of fossil fuel. The coatings used to preserve these boards after installation in outdoor construction also leave a footprint, whether through the manufacturing process or disposal.

Should a woodworker selectively weigh and use various environmental claims when offering choices to his/her customer? If a shop is going to build a lot of outdoor structures using either WPC products, pressure-treated wood or natural lumber, it seems the estimator and salesperson should do a little independent research before promoting any one industry’s claims.

Aesthetics and other concerns

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The litmus test for most deck material choices is probably not cost, durability or environmental factors. It’s often as simple as the look that the customer wants. Some people just want wood and there’s no substitute as far as they are concerned. A handsome, well-designed ipè deck is a beautiful thing to see. Others want the clean lines and low maintenance of a composite structure and, with the number of colors and textures available now, there are lots of aesthetic choices available.

One of the drawbacks to some composite materials is that they can be slippery when wet. To that end, manufacturers have introduced a variety of ribbed, grooved and even grain-textured finishes that offer shoes a little more grip, and for elderly clients especially, this improved footing can be comforting. Certain types of shoe soles also work better on impervious, plastic-based decking: check with the WPC manufacturer for recommendations.

If cost is the primary concern, pressure-treated lumber seems like the obvious choice. It is billed to last longer, the initial cost is relatively low, and availability is widespread. Handling and working with this material usually calls for gloves and masks: check with the supplier as to the mill’s health and safety recommendations. Most composite or imported wood decks are built upon a substructure of pressure-treated framing, so it’s a good idea to become familiar with the standard cautions and warnings before sending out your crew to work with any of these products.

This article originally appeared in the August 2014 issue.

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