Published on December 17th, 2007 | by Stephanie Evans13
Sustainable Decking Solutions
Building a truly green deck is a big challenge. We want our decking materials to do things that they do not naturally do, such as last for many years without a lot of maintenance. Most of the ways we’ve found to accomplish this have significant negative environmental effects.
Even materials that seem to be ecologically sound sometimes don’t hold up under closer scrutiny, while others that initially appear to be environmentally destructive often provide a more sustainable choice.
Natural wood decks have advantages that no other decking material possesses:
- Wood is nontoxic and extremely strong for its weight, and it is beautiful and easily worked.
- Wood is a renewable resource if it’s intelligently managed and it’s produced with comparatively small fossil-fuel inputs, especially if harvested products come from forests that are local to the buyer.
- Wood is also easy to reuse and recycle and it biodegrades without any polluting byproducts.
The problems associated with wood decking surprisingly spring from its advantages: The natural inclination of your beautiful wood deck is to return to the soil from which it came, by the action of weather, insects, bacteria, and molds. To delay this effect, woods that have innate rot-resistance, such as native cedar and redwood, are commonly used, in addition to imported tropical hardwoods such as teak and ipe (a Brazilian hardwood pronounced ‘ee-pay,’ also known as ironwood).
It is worth noting that the famed rot-resistance of redwood is considerably greater in lumber made from old-growth trees. This wood is now unavailable except as recycled wood from old buildings. If recycled redwood or cedar is available in your area, it is worth seeking out, both to conserve natural resources and as a superior material. Another consideration is that the farther away the wood is grown, the greater the carbon input involved in getting it to you.
Wood is a product of forests that can be managed for the benefit of the whole planet, but most often, they are not. Clearcutting and monocropping degrade and deplete our forestlands. To support sustainable forestry practices, look for wood certified by the Forest Stewardship Council (FSC).
Naturally rot-resistant wood is wonderful stuff, but as human pressure on forests increases, these woods have become more and more expensive, forcing people to search for most cost effective alternatives. A popular substitute, especially in areas far from cedar and redwood forests, is decking made from less rot-resistant, cheaper softwoods that are pressure-treated with various chemicals that inhibit decay.
The degree of a wood’s rot-resistance depends upon the depth of treatment—wood that is in contact with damp soil needs the deepest treatment. Treated decking can be finished with stains and paints much like natural wood (with some adaptation), and it retains all the strength of natural wood.
Pentachlorophenol, creosote, and chromated copper arsenate (CCA) were once the standard wood preservatives. All of these are extremely toxic and somewhat less poisonous treatments, such as amine copper quat (ACQ) and copper azone (CA), are starting to replace them for residential use. The safer alternatives are still far from benign, however.
- ACQ- and CA-treated wood cannot be recycled or burnt—it’s toxic to produce, work with, and dispose of. To learn more about treated lumber, visit this article about The New Pressure-Treated Wood.
- Currently the best alternative wood preservative is borate. Borate is water-soluble, meaning that it cannot be used in ground-contact situations, but it is fairly inert and non-toxic. For more information, download this PDF fact sheet on Borate-Treated Wood for Construction.
Deck Stains and Preservatives. Even if your deck is made of natural wood, most finishes designed to keep its appearance fresh and to retard decay are bad for the environment and for you. Follow this link to an informative page about Wood Preservatives and Outdoor Finishes. Also, look for low-VOC, low-toxicity finishes made by such companies as AFM Safecoat, Bioshield, or Eco Safety, among others.
As we design and modify our living spaces, let’s look "beyond the porch" and keep an open mind for sustainable options. After all, there are many other ways to sit outdoors . . .
Composite decking products blend waste wood fiber and recycled plastics, adding in waxes, fiberglass, and preservatives to form wood-like boards. Popular manufacturers known for sustainable products and practices include Trex, Nexwood, and Timbertech, and others.
Some products last up to 20 years with little maintenance; however, all will weather and warping are not unusual. Composite lumber has some of the strength of wood, it looks and feels something like it, it can be worked with wood tools, and it uses waste products that might otherwise end up in a landfill.
In terms of green building, the biggest objection to composite decking is that, although it lasts a long time, it is very difficult to dispose of once it reaches its life’s end. This is because its biological components (wood and other cellulose) and "technical" components (plastics, waxes, and fiberglass) are inextricably blended.
In a well-designed recycling system, biological wastes are allowed to decompose naturally, while technological wastes such as metals, chemicals, and petroleum products are filtered out for reuse. So far, there has been no progress in meeting the recycling challenge of composite wood products. To learn more about composite decking, see:
- The Healthy Building Network’s Guide to Plastic Lumber
- This UC Extension article, Composite Lumber for Consumer & Residential Applications, which includes an appendix with ratings for various plastic lumber products
Lumber made entirely from High Density Polyethylene resin—the same stuff milk jugs are made of—is made from plastic waste that easily makes another turn around the recycling wheel. Like composite lumber, it is workable with wood tools and is available in a variety of colors and textures.
Plastic lumber does not possess the strength of wood and it is thus best suited for low-load structural applications, such as tables, benches, or planks on well-supported walkways. It is not intended for primary structural load-bearing elements, such as posts, joists, and beams. Compared to composite lumber, HDPE plastic decking products:
- tend to expand and contract more with temperature
- are not as strong
- have an increased tendency to warp
Manufacturers of plastic lumber vary in their use of post-consumer waste. Look for products which contain at least 50% post-consumer waste plastic.
One green building idea with a lot of merit is treating wood as a luxury. Trees help the planet the most when they’re alive and globally, the acreage per forest is dwindling rapidly. Using wood as a common structural and outdoor finish material is not a long-term sustainable practice.
Many industries will soon have to get creative in looking for sustainable, cost-effective alternatives. Trying to mimic wood with plastic has its limits too, since plastic has little of the strength and few of the aesthetic charms of wood.
Instead of trying to make other materials be wood, or trying to make wood last long past its natural lifespan, we could think of ways to make usable outdoor spaces without decks. Wooden decks are a modern phenomenon. There are many other traditional treatments of outdoor living spaces that we could learn and profit from.
- Mediterranean- and Mexican-paved patio, for example, uses the durable, low-cost, low-maintenance, and non-toxic recyclable materials of tile, concrete, and stone.
- English garden design offers the brick or stone terrace, adaptable to sloped sites.
As we design and modify our living spaces, let’s look "beyond the porch" and keep an open mind for sustainable options. After all, there are many other ways to sit outdoors…