Alter Eagle Construction
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Alter Eagle Construction & Design
Composite Decking
Deck components can be divided into structural (posts, joists and
stringers) and non-structural (decking and railing) parts.
components are almost always made from pressure-treated wood
, but there
is more variety in decking and railing.
In fact, the most popular decking and railing materials are pressure-treated
wood, at about 80 percent of the market, followed by woodfiber-plastic
composites (WPCs)
, at 8 percent, redwood (6 percent), cedar (3 percent),
plastics (2 percent) and other materials (1 percent).

The Advantages
Most homeowners want building products that look good and perform
well at low cost. Most WPC decking products look very good, at least
when they are new. Judging from the growing WPC market share, it
seems many do-it-yourselfers and homebuyers agree.
Another important aspect of the overall positive look and feel of WPC
decking is the straightness of the boards and their consistent
The Disadvantages
WPC decking is more expensive than conventional pressure-treated stock.
It depends on the market area, but expect to pay 60 to 70 percent more.
With the large variety of different designs and compositions of WPC
decking, it can be hard to make generalizations. The types that have a
solid cross-section (rather than open channels) are usually quite dense,
making the boards about twice as heavy as conventional treated solid
wood. This makes the decking more difficult to handle and translates into
increased labor costs.
The Bottom Line
There is no doubt that there are a lot of advantages to using woodfiber-plastic deck boards. The lack of
splinters and the use of no wood preservatives are especially important for many people.
The major confusing factor is the large variety of products on the market. How do you choose which one
to use on your deck? I would be especially concerned about what the decking is going to look like in a
year or two. The boards will weather differently in different environments.
The safest approach is to look at what products are available locally, choose a couple based on your
taste, then ask the retailer if they can point you to local installations of those products. Then you can
get an idea of the color changes, potential for mold growth in your climate, and surface wear that can
Color changes should also be taken into account during deck design. Initially, a composite deck board
may have the same color as solid wood. But are they going to weather to the same color? If you have
large areas of wood exposed in your design, as well as the composite decking or railing, you may notice
the wood and composite areas look very different after weathering and don't coordinate as well. Also,
remember that composite deck board designs with an open cross-section look best if the ends are
covered with a trim board.
You should read the installation instructions before you buy. If you are not prepared to pre-drill holes,
don't buy a product for which this is required. Don't expect these products to behave the same as
treated wood.
Because these are relatively new products on the market, there is not a long history of use. The
manufacturer's brochure will typically show beautiful, freshly built decks. You want to know what your
deck will look like after a few years? Read the brochure and warranty carefully, and if possible, look at
the product after it has been in service for a few years in your area
Trex Deck (madeira red) : The Petaluma Project
The rapid growth in composite decking is one of the most exciting stories in recent residential
construction. It went from a market share of 2 percent in 1997 to about 8 percent in 2000 and is
projected to have a 20 percent market share in the United States by 2005.
It is generally agreed that a WPC is a mixture of a thermoplastic, such as polyethylene (commonly used
to make plastic toys and milk containers, plus a lot of other products), with wood flour or fiber, with at
least 40 percent of the composite being wood.
All the current products are formed by extrusion. A hot mixture of plastic and wood particles plus a
variety of additives are squeezed through a die, like toothpaste out of a tube, then through a cooling
section to harden the plastic. The continuous extruded product is cut to appropriate lengths, usually 16
feet. The shape of the die determines the cross-sectional shape of the deck board.
A deck construction detail
appearance. There are no knotholes or areas of raised grain, as you can find with treated solid wood.
You also cannot get splinters from WPC decking - a major advantage if you have small children running
around on your deck with bare feet. Some decking products also have a roughened surface that provides
good traction, even in the rain.
WPC decking is also more dimensionally stable than solid-wood products. A common problem with
conventional treated-wood decking is shrinkage after installation. It can be very frustrating to have the
initial small, even spaces between your boards open up to yawning crevasses after the wood boards dry
and shrink.
Installed gaps between composite deck boards stay the same after use. Manufacturers also claim WPC
decking does not warp, cup, twist or cause loosening of fasteners. Similarly, these products do not
require much maintenance
compared to solid-wood decking. Staining, waterproofing or sealing the
surface is not necessary.
There are also environmental advantages. The wood component is typically sawdust and/or planer
shavings from lumber mills, or ground-up shipping pallets and other wood packaging materials. These
composites allow efficient use of forest resources.
Many manufacturers use plastics that are recycled. In fact, plastic-based building products were
originally developed to be a major consumer of recycled plastics. The volume of WPC products has,
however, outgrown the supply of recycled plastics, so the industry now consumes a lot of virgin plastic
as well.
Another related environmental issue deals with wood preservatives. WPC decking typically does not
contain any wood preservatives. It is considered to be inherently resistant to decay fungi and insects
. All
the issues surrounding arsenic and other heavy metals in pressure-treated wood are avoided.
All these characteristics lead to a low-maintenance, environmentally friendly deck, but there is a cost.
Trex Deck (madiera red) : The Barnett Valley Project

That problem is overcome with the non-solid designs. The high density can also be a problem for
fasteners; pre-drilling is often necessary. Even countersinking screw heads may be required, although
some new designs avoid that need. Again, this adds to labor cost.
One property that is consistent, however, is that all WPC decking products are substantially weaker
than solid wood. For decking, stiffness is particularly important. With solid-wood decking, you can often
use 24-inch centers for the joists. You should use 16-inch centers for composite decking
, which also
can increase the total cost for the deck, because more joists may be required. Of course, the same
spacing considerations apply to stringers when composite boards are used for steps.
In some warm, moist climates, some WPC products are also initially prone to mold growth. This
typically happens immediately after installation. The mold will grow until the nutrients on the composite
surface are used up, then the boards will be mold-free afterward. If this happens, the deck surface can
be cleaned with a diluted bleach solution, or plain soap and water. This temporary problem usually
doesn't affect long-term performance.
Some of the WPC deck boards have a glossy or semi-glossy surface that can look very good, but
remember that the surface is soft and prone to scratching and wear. Moving barbecues, plant pots or
patio furniture can easily scratch the surface. Scuffs from just walking on the surface can lead to wear
patterns. The surface of the boards near doors or down the center of steps can soon look much duller
than surrounding areas. For some people this can be a real problem.
The decking products with an open-channel structure to them have some advantages - they are less
dense per foot of board, and they may be cheaper than the solid boards. One thing you have to be very
careful about with these designs is the placement of fasteners. Over-driving a screw at the center of a
channel can crack the board or at least cause a large indentation in the board surface.
Components | Advantages | Disdvantages | Bottom Line
A deck detail