How Composite Decking Works

Hate making decisions? Well, lucky for you there are only two types of comp­osite decking on the market: solid and hollow. Solid looks more like wood and is heavier than the hollow version. Because of its greater mass, solid decking will expand and contract more with temperature fluctuations.

Hollow composite decking has a more man-made look. However, it won't expand and contract as much as solid composite decking. You need to be careful when handling it, though, because it's more susceptible to damage before it's installed. Solid composite decking is more popular because of its superior strength and closer resemblance to real wood [source: Montenegro].

Regardless of the type of composite decking, it's important that the product is treated with a preservative and antifungal chemical. When left untreated and exposed to the elements, most wood will rot over time. Excessive moisture accelerates the rotting process. Even though the wood fibers and other cellulose in the decking have been combined with plastic, it can still rot, according to the Forest Products Journal. Considering that most composite decking products consist of at least 40 percent wood (sometimes as much as 70 percent), the lack of a preservative could cause serious problems. And some composites have wood contents as high as 70 percent [source: Carter].

The preservative is mixed in with the wood during the manufacturing process. Some preservatives, like zinc borate, can remain active in composite decking for more than 20 years.

There are three types of composite decking material: polyethylene-based, polypropylene-based and nonwood plastics. Oil-based polyethylene and polypropylene composite decking contain some wood. The industry seems to be moving away from polyethylene-based composites to focus on the polypropylene-based product (which is typically stronger and less susceptible to expansion and compression) or polyvinyl chloride (PVC)-based product. These plastic­s have no wood content, do not stain or absorb water. Technology is enabling manufacturers to give all these composites a look and feel that approximates real wood. [source: Descoteaux].

A variety of factors come into play when you're choosing the material for a composite deck, such as cost, availability of color and a hidden fastener system. Composite decking is more expensive than wood, but how much depends on the particular product. Nonwood plastics are significantly more expensive than real wood, are lighter than the other composites, and typically don't contain any recycled content.

The color and desired textures of the deck, where the deck is located and how the deck will be used will help narrow down which the best product [source: Decks].

Some of the big manufacturers are ChoiceDek, EON, Epoch Evergrain, GeoDeck, LP Weatherbest, TImberTech, Trex and Veranda. The industry is evolving, with efforts being made to eliminate some of the stain, fading and mold issues that composite decking has been known for. Here are details on some of the products:

For particulars about installing composite decking, read on.

While the materials for a composite deck are more expensive than most wood, installation costs are fairly comparable. The same foundation of pressure-treated wood is used for both wood and composite decks, but there are several differences between the way wood and composite decking is gapped and supported.

Note: There is now a plastic lumber, USPL's TriMax, which can be used for structural applications. However, unless accommodations are made to oversize the joists and/or space them more closely, the deck can be bouncy [source: Hardy].

Manufacturer's specifications will guide the size of the gaps required for the composite decking. Gapping (between boards and between the decking and an abutting wall) is necessary to accommodate the expansion and compression that is inherent in composite decking. To determine ho­w many fasteners you'll need for a deck installation, multiply the number of joists by the number of decking boards.

Composite decking is weaker than wood. Installing a composite deck on a foundation originally used for a wood deck will require more joists. You'll also have to adjust the framing if the decking is installed in a pattern, like a herringbone or tile pattern [source: Hardy].

Drainage and airflow are crucial to keeping composite decking from degrading. To install composite decking over a solid surface, you need to build a sleeper system. The surface below the deck needs to be pitched for drainage or outfitted with a gutter system, such as TimberTech's DrySpace Drainage System, designed to drain the water from underneath the decking.

Also, the type of composite decking will dictate certain parts of the installation. For hollow decking, you need to use a picture frame design or a starter strip. The starter strip covers the end of the first piece, hiding the fact that it's not solid. Hollow decking also needs a screw at every junction where a joist meets the decking board [source: Descoteaux].

One final note: While most composite decking manufacturers offer warranties on their products, the warranty will be void if the installation does not precisely follow the manufacturer's directions, because a bad installation can result in a degraded, unsafe deck.

To learn more about composite decking, visit some of the following sites.