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ENVIRONMENTALLY FRIENDLY DECKING THAT MAKES THE CUT (03/28/2011)

By Brent Gwatney, Construction Executive Magazine

Due to performance advantages and aesthetics, as well as appealing environmental attributes, composite decking has become the fastest growing segment in the decking market. Its weather resistance, versatility and long lifespan make it ideal for commercial decks, docks, boardwalks and a variety of other applications. With many composite decking products to choose from, a little research can go a long way to ensure the material chosen meets the goals for a project.

Not All Composite Decking Is Created Equal

Most wood-plastic composites combine polyethylene plastic, wood fiber and a variety of additives that help stabilize the plastic, enhance color and protect the decking from UV damage, mold and mildew.

While the same or similar ingredients may be used in all wood-plastic composite decking, each manufacturer has its own product formulation and processing technologies.

Using recycled content, for example, is not universal. Some manufacturers use only virgin materials, while others incorporate varying amounts of recycled content. Many composite decking product manufacturers that include recycled content often omit the details on specific amounts of pre- and post-consumer content. Therefore, it is important to find out exactly what percentage of the product is made from recycled materials. The amount can range from zero to 95 percent. (Additives and color agents are typically included, preventing decking from being considered 100 percent recycled content.)

In addition, determining whether the recycled materials come from pre-consumer or post-consumer channels also helps contractors choose the most environmentally friendly product. Pre-consumer materials are generated by manufacturers and processors and may consist of scrap, trimmings and saw dust. Post-consumer material is waste that has been used and disposed of by consumers and diverted from landfills.

Composite decking that contains a high percentage of post-consumer recycled content is considered to be more environmentally friendly, helping contribute to green building rating points in LEED and other programs.

Decking Performance

Durability and performance also are important considerations when choosing decking materials. Composite decking performance depends on how it is made and how the plastic surrounds and bonds to the wood fibers. Most commonly, manufacturers mix wood fibers with plastic and then heat and extrude the material into deck boards, railing and similar components. The plastic serves as a binding agent and protects the wood fibers from moisture, while the wood filament adds stiffness, reduces thermal expansion and flammability, and gives the deck boards the look of natural wood. If the wood fibers are not entirely encapsulated, or if they become exposed over time, the deck boards can absorb moisture and be susceptible to mold, mildew, discoloration and, in some cases, decay.

To prevent exposure of wood fibers, select products are made with a total encapsulation method in which wood fibers are aligned and completely surrounded by plastic. The resulting product absorbs substantially less moisture than solid wood and other composites, and is more resistant to rot and insects. These characteristics allow composite deck planks to be used in applications that have direct contact with the ground (such as landscape trim) and water (such as marina decking, dock surfaces and commercial boardwalks).

Wood-plastic composite products are splinter-free, slip-resistant and do not twist, split or crack. Under typical conditions, composite decking is expected to last two to three times longer than traditional wood decking materials.

n addition to environmental attributes and performance characteristics, the appearance of composite decking varies. Due to different manufacturing techniques, composite deck boards come in many textures, colors and profiles. Some brands come closer to resembling real wood than others.

The most popular composite deck boards have deeply embossed wood grain textures and finishes that emulate the look of tropical hardwoods. Color choices range from gray to warm hues, providing contractors a range of options to complement existing structures. Most composite decking will weather to a slightly lighter shade within three to six months of installation, depending on exposure.

Composite deck boards are available in solid, hollow or ribbed profiles, and with or without grooved sides for hidden fastening systems. Solid planks are the most similar to sawn-lumber in appearance and handling. Hollow composites are generally lighter, but don’t bend as easily as solid composite boards, and typically require trim or end caps.

Design and Installation

Manufacturing methods allow composite decking to be shaped, cut and installed in ways that are not possible with lumber. Composite deck planks can be bent for use in applications such as stairs, benches and walkway arches, as well as any surface or non-structural features that call for round edges. This enhanced flexibility can save contractors time and trouble when building complex deck and dock designs that include curved boards.

Decorative railing accessories, including posts, post caps, balusters and trim boards, also are available in some composite decking product lines. Certain railing accessories incorporate convenient details, such as hollow posts, for easy installation of outdoor lighting (including solar) and audio equipment.

Composite materials can be easily machined and installed with standard hand and power tools. To attach composite boards to underlying structural members, contractors can use nails, screws or hidden fastening systems. However, not all composite decking products are compatible with each method, so it is important to follow the manufacturer’s recommendations.

Also pay close attention to maximum allowable uniform live load and member span requirements under local building codes.

Composite decking does not require staining or sealing, but periodic maintenance is necessary to maintain aesthetics and prevent mold and mildew. Commercial deck cleaners are generally suitable and include eco-friendly options.