Eco-Friendly Extends Life of Decking

Brent Gwatney is vice president of sales and marketing for MoistureShield composite decking.

Demand for decking and railing in the U.S. will increase by 8 percent per year through 2013, according to research group Principia Partners. Currently, plastic-based synthetic products account for 34 percent of the market, and are expected to continue their steady growth. Within the synthetic decking segment, wood-plastic composites (WPCs) continue to dominate.

The shift to wood-plastic composite decking has been a growing trend over the past five years as interest in long-term durability and environmental benefits have increased.

Its use of recycled content, resistance to rot, moisture and insects and attractive appearance have made composite decking an increasingly more common building material in commercial applications.

Frequent exposure to sun and rain, and in some areas snow, heavy foot traffic and contact with destructive insects, can take a toll on decking surfaces. The performance characteristics and durability of wood-plastic composites can allow it to endure such exposures better than traditional wood decking, extending the life and looks of patios, decks, pool and hot tub surrounds, light-duty docks and boardwalks.

In the Making

Prior to their introduction as a decking material, wood-plastic composites were used primarily in high-exposure applications like window and door components where durability and moisture resistance are crucial.

After observing their proven performance in these systems, manufacturers recognized the benefits wood-plastic composites could offer in exterior surfacing and set out to create the first deck boards.

Although wood-plastic composite decking has come a long way since it hit the market over 20 years ago, the ingredients are largely the same. Most commonly, wood-plastic composites are made with a combination of polyethylene plastic, wood fiber and small quantities of additives that help stabilize the plastic, enhance color and/or protect the decking from UV damage and mold and mildew.

A typical ratio of wood to plastic is 50/50, although wood content varies from a few percent up to 70 percent. This ratio, along with the specific product formulation and manufacturing process, will determine how well the decking will perform over time in various climates and applications. For instance, increasing the wood fiber produces stiffer boards, but above 65 percent wood content, there is a lower probability that the plastic will fully encapsulate the wood fibers. If the wood fibers are not fully encapsulated, they become vulnerable to insects and moisture absorption, which can lead to mold and rot, and decrease the overall lifespan of the deck boards.

Problems due to moisture absorption are among the reasons why some composite decking manufacturers have recently introduced cap stock composite boards, which feature a PVC outer shell surrounding a wood-plastic composite core.

However, some composite decking is manufactured using methods that ensure total encapsulation of the wood fibers in plastic throughout the board, eliminating the need for an outer layer of PVC. With wood fibers enclosed and protected in plastic, the resulting product is moisture, insect and rot resistant. These characteristics allow materials such as MoistureShield composite decking to be installed on the ground, in the ground or in the water, without voiding the warranty, as well as in a range of exposures and weather conditions.

Composite products provide lower thermal expansion than all-plastic decking, further supporting the material’s performance in harsh environments. In variable climates, wood-plastic composites may be more suitable for decking than plastic materials, as the latter tend to expand and contract more with temperature changes.

Composite materials also resist splintering, twisting, splitting, and cracking. A splinter-free, slip-resistant surface makes the material suitable for playground equipment, access ramps, outdoor showers, and in recreational facilities where safety is a concern.

Under typical conditions, composite decking is expected to last two to three times longer than traditional decking materials. To help ensure selection of quality products, check available warranties, as product formulation and performance vary. Some manufacturers offer limited warranties ranging from 20 years to lifetime.

In Green Building

While some composite decking products are made with virgin materials, most include at least a small percentage of recycled wood and/or plastic. The amount of recycled content can range from five to around 95% (additives and color agents prevent the decking from being considered 100% recycled content).

The percentage of recycled materials coming from pre- and post-consumer channels also varies by product. Pre-consumer sources include food packaging waste, pallet wrap, construction debris, wood pallets, and fiber waste from sawmills. Milk jugs, grocery bags and detergent bottles are some of the post-consumer items that are diverted from landfills. To find the recycled content percentages for composite decking, consult the manufacturer’s literature or website.

Depending on the percentage of pre- and post-consumer content, composite decking can help earn points in green building rating systems. Under LED for New Construction and Major Renovation, one or two points are possible for the use of materials with recycled content. To earn one point in the Materials & Resources category (MR-4), the sum of a material’s post-consumer recycled content and one-half of its pre-consumer content must total 10 percent or more. For two points, the threshold is 20 percent.   Some products exceed this benchmark by a factor of three, with calculated scores of 67 percent (e.g., 38 percent post-consumer plus one-half of 57 percent pre-consumer content).

In addition to recycled content, composite decking may be able to help earn credit in other categories as well, including regional material sourcing, bio-based materials, prefinished materials, and termite-resistance, depending on the program.

In Design

The most obvious advancement from earlier versions to today’s composite decking products is in aesthetics. Once very plastic-like and shiny with little to no surface detail, composite deck boards today are available that closely resemble popular wood species, including tropical hardwoods, with realistic colors and embossed grain patterns.

Color options can include gray and terracotta to cedar, mahogany, tigerwood and walnut, depending on the brand. The wide selection of colors provides many options to enhance visual interest by combining colors for inset designs and patterns or to complement existing structures. 

Further enhancing design flexibility, composite deck planks can be bent for use in stairs, benches and walkway arches, as well as any surface or non-structural features that call for round edges. This characteristic can save time and trouble in complex deck and dock designs that include curved boards.

Like wood decking, most composites will weather to a slightly lighter shade within six months of installation. Some manufacturers incorporate extra pigment to offset the fading, but it is best to check with the manufacturer and ask to see a sample of a weathered board prior to purchase.

Composite deck boards come in multiple profiles, including solid, hollow or scalloped, 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.

Decorative railing accessories – including posts, post caps, balusters – and trim boards are also available with most composite decking product lines. Composite deck tiles provide another surfacing option that is attractive and quick to install on patios, balconies, and rooftops. Like composite deck boards, composite deck tiles are resistant to rot, moisture and insects, and can be made with recycled content. The tiles and composite deck boards can be used in conjunction to enhance virtually any hard, level surface.

Installation & Maintenance

Building codes typically allow composite deck boards as surfacing for exterior balconies, porches and decks and as stair treads, but not structural elements. Composite railing systems can be used in a range of applications. Building professionals generally can utilize composite decking and railing in any occupancy group in type V-B construction under the International Building Code (IBC) and in buildings constructed under the International Residential Code (IRC).

To confirm a brand’s conformance with codes and the ICC-ES Acceptance Criteria for Deck Board Span Ratings and Guardrail Systems (AC174), the International Code Council Evaluation Service (ICC-ES) issues evaluation reports.

For dry and windy climates like parts of Arizona and California where wildfires pose a threat to buildings, wood-plastic composite decking options are available that meet ignition-resistant construction standards. California’s Department of Forestry and Fire Protection lists such approved products in its Wildland-Urban Interface (WUI) Products Handbook.

Composite materials can be easily machined and installed with standard hand and power tools. To attach composite boards to underlying structural members, screws, nails or hidden fastening systems can be used. However, not all composite decking products are compatible with each method, so it is important to follow manufacturer recommendations. Understanding local code regulations and substructure requirements for spans is also essential. Close attention should be paid to maximum allowable uniform live load and member span requirements.

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 alternatives.