The Deck Handbook: Part 6
How to Buy a Composite Deck

If despite all the risks and uncertainties, you decide you cannot live without a composite deck, then buy wisely. The key to buying a composite deck is, like any major purchase, research, research, research. Here is the information you will want to have to make your decision.
The first rule is to never buy composite decking without seeing it. You will want to know what is really looks like, and only an in-person, eyeball inspection can tell you. Buying from photographs on line, no matter how accurate the depiction, is a recipe for disaster.
Secondly, disregard the manufacturer's brochures, flyers and videos. These show you only what the company wants you to see. But, you want also to see all the not so good things about the product, or, at least, the product in a neutral setting before you commit many thousands of dollars to buying it. Two documents will give you this information, the decking warranty and its material safety data sheet. Do not buy any composite decking before reading and understanding both of these.

Composite Decking Warranties — Reading Between the Lines

We get lots of materials promoting various composite decking. They come through the mail, via the internet, and in the trade journals we all have to read just to keep up with the ever-changing remodeling environment. We pretty much ignore them all.
If we want to find out what a composite decking manufacturer really thinks of its product, we turn immediately to its warranty.
A company may gush at some length in its advertising over how long its composite material will last, and how well it will hold its color without fading, and how little maintenance it requires. But, this is all just talk. The real truth comes out when the company has to break out its wallet, and that truth is in the written warranty. The warranty tells the real story of how much faith the manufacturer actually has in its product.
"The company may gush at some length in its advertising over how long its composite material will last, and how well it will hold its color without fading, and how little maintenance it requires. But, this is all hot air.

The real truth comes out when the company has to break out its wallet, and that truth is in the written warranty. The warranty tells the true story of how much faith the manufacturer actually has in its product."
A good example is the Trex stain warranty. One Trex brochure for its capstock Transcend decking boats that it "resists everything but stares." But, what does the company actually guarantee? Go to its 25 year fade and stain warranty, and you'll see that the decks's "resistance" is limited pretty much solely to permanent staining from food and beverage spills. If anything else stains the deck — bug spray, lawn mower oil, the dog poop your kid tracked in after playing with the new puppy next door, weed killer — you are on your own. Trex won't pay to fix it.
If a manufacturer warrants its "lifetime composite" for twenty years, then that's the real life expectancy of the deck — 20 years.
But, even that's not the whole story.
Few composite decking manufacturers will voluntarily pay all of the cost of replacing defective. Most agree only to replace the defective materials. Some won't even pay for the shipping to get the replacement materials to your driveway — where they are usually dumped with little ceremony. But, it's the labor that is the expensive part. Removing and hauling the defective materials to the landfill, and installing the new decking will probably cost you nearly as much again as the original cost of your deck. One or two manufacturers have enough faith in their products to pay labor for a short time, none longer than 5 years, but most do not.

Deck Calculus. Lifetime Costs: Composite v. Wood Deck

The real cost of a deck is its lifetime cost. Composite manufacturers a few years ago made lifetime cost a big deal in their advertising and sales materials. The idea was that while composite decks are more expensive to build, they require less maintenance over their lifetime, so the lifetime cost of a composite deck is less than that of an equivalent wood deck.

As problems surfaced with composite decks, and coatings for wood decks got better and longer lasting, these claims have all but disappeared. Still, lifetime costing is useful information, so let's compare a treated pine deck with a typical composite.

Assumptions: We assume, first of all, that you will carefully select your composite deck and avoid those that fade excessively, delaminate or harbor mold and mildew so all that will be required is routine cleaning. You will build your comparison wood deck out of ACQ treated pine. Each deck will be built according to building code and in a workmanlike manner using generally accepted construction practices. You are 35 years of age, so your life expectancy is another 50 years or so. This is how long we want the deck to last.

Initial Cost: The cost of the composite 16' x 20' deck built by Remodeling Magazine is $15,368 (See sidebar "How Much Does it Cost?", above). The cost of the same deck in ACQ treated pine is $10,546. Now we have to stain and seal the wood deck at an additional cost of $440.00, so its total cost, including sealing, is $10,986. You would save $4,402 in initial construction costs by building a wood, rather than a composite deck.

Routine Cleaning and Maintenance: All decks require brooming at least once a week and deep cleaning periodically. This is true whether your deck is wood or composite. Most composite manufacturers recommend a good washing every six months or so, once in the spring and once in the fall. This is also a good schedule for wood decks. So, routine maintenance for both types of decks is the same. Figure about $100.00 to have a professional deep clean your deck every six months. Over the 50-year lifespan of the deck, you will spend $9,900 to clean your deck. The cost is the same for both types of decks.

Staining and Sealing: Assuming your composite deck never has to be sealed or stained, we will not price staining or sealing for the composite deck. Of course, if its fades or begins to deteriorate and you decide to stain and seal to protect the deck from further damage, then your cost will be similar to the cost of periodic staining and sealing of a wood deck.

We gave your wood deck a good coat of stain and long-lasting sealant when it was built, so it's good for five years or so. But, at the end of that time, you will need to reseal your wood deck. This will cost, in today's dollars, about $400. (This is less than the cost of the first staining and sealing because the underside of the deck is usually requires no resealing since it gets very little exposure.) You are going to reseal your wood deck eight more times before the deck is torn down 50 years from now, for a total resealing cost of $3,600.

And, The Winner Is…
Deck TypeInitial CostCleaning
Lifetime Cost
Composite Deck$15,368$9,900N/A$25,268
Treated Pine (ACQ) Deck$10,546$9,900$3,600$24,046

Of course, if you do the work yourself, then the cost savings of the wood over the composite deck are more striking. However, be careful washing a deck. Wood decks can stand power washing, but most composite manufacturers recommend against power washing, and suggest that if you do power wash, use very low pressure.
Moreover, most composite deck warranties are also pro-rated. The company will pay 100% of the cost of replacing defective materials for the first few years of the warranty, then decreases the amount it will pay to as little as 2% in the final year. So the manufacturer can advertise it "30-Year Limited Warranty" in bold print, but it's really just a 5-year warranty — and a limited warranty at that. What the manufacturer is telling you with this warranty is that it expects 98% of its decks to have failed by the end of the warranty period, only 2% of them are expected to survive. If more survive, that's great, by the company is not willing to bet its own dollars on it.
Why so chincy? Because no one, and that includes the manufacturers, knows what this stuff will do over the long haul.

Guaranteeing an Experimental Material

Ccomposite decking is, unlike wood, an experimental material.
Wood is well-understood. We have been working with it for well over a hundred thousand years. By now we're pretty sure how to build things out of it, and how long those things will last.
Engineered composite decking is new. Most of what is on the market now was introduced during the Obama administration. It is a largely untried material about which only a few things are actually known. The rest is guesswork and estimates.
The life expectancy of composites is not at all certain. Very few composite products have been around for as long as 5 years, much less 25 years. Composites are lab tested, and from these tests scientists and engineers estimate how long they are likely to last in the real world environment. Scientists and engineers can be, and often are, wrong. Making a composite is an inexact science at best (see "Cooking" Composite: More Art than Science). Trex, Westherbest, GeoDeck, and Veranda all bet on durability and life-expectancy estimates, and lost. Their decking came apart within a few years. They were sued and had to pay out large amounts of money.
The guinea pig in the long term testing process, unfortunately, is you, the homeowner, who buys and installs composite decking. If it turns our that the laboratory predictions were wrong and the decking does not hold up as expected, your warranty claim, combined with hundreds of others, tells the company it needs to fix something. For the company this is very cheap product research — to give you a retail dollar's worth of decking costs the company just 25¢ — but, for you, the homeowner, it is often a financial disaster a s you spend more thousands of dollars to rebuild a deck that you already spent thousands of dollars building in the first place. And that, as bad as it may be, is actually not the worst case scenario.
The worst case scenario is the company pays you nothing for its mistake. If the composite deck material failure is systemic and widespread, and the cost of honoring the company's warranty potentially catastrophic, as was the case with GeoDeck and Louisiana Pacific products a few years ago, the companies just declare bankruptcy or sell their assets and go out of business, leaving you, the customer, high and dry with no recourse except to shoulder the full financial burden of fixing or replacing your defective deck.
"The guinea pig in the actual long term testing process is you, the homeowner, who buys and installs composite decking. If it turns our that the laboratory predictions were wrong and the decking does not hold up as expected, your warranty claim, combined with hundreds of others, tells the company it needs to fix the material.”

“For the company this is very cheap product research — to give you a retail dollar's worth of decking costs the company just 25¢ — but, for you, the homeowner, it is often a financial disaster as you spend more thousands of dollars to rebuild a deck that you already spent thousands of dollars building in the first place."

What's Not In the Warranty?

But, while it is important to carefully read a composite decking warranty for what it says, it is also important to read it for what it does not say.
If the company does not mention mold or mildew in its warranty, what does that tell you? Simple. If there is no guarantee against mold or mildew, the manufacturer expects mold and mildew to form on its decking. If there is no guaranty against color fading, the deck is expected by its manufacturer to fade over time. Does the company warrant against against staining. No? Then the company expects the deck to stain.
So, understanding what is not covered by the warranty is just as important as understanding what is covered. The simple rule of thumb is, if it is not mentioned, it is not guaranteed. If its not guaranteed, the company expects the worst to happen. And, who should know better than the company what to expect?

What's It Really Made Of?

What is the composition of the decking material? We know that the core ingredients in wood-plastic composite are wood (or a substitute filler like rice hulls or straw) and plastic. But what else is inside the composite? Actually, WPC composite decking is a complex chemical soup that contains wood (or wood-like substances in some form) and a plastic, but also numerous mineral and chemical additives.


Proper additive choices for composites are critical to both performance and manufacturing. Included in these are…
  • Stabilizers to help the material mix together evenly,
  • Waxes and lubricants that help the product move through the extruder without binding,
  • Stiffening agents to keep the material from flopping around during manufacturing like strands of spaghetti,
  • Foaming and blowing agents that reduce the heat caused by friction in the extruder and help the product expand evenly,
  • Colorants to give the board its "realistic, wood-like" color,
  • Coupling agents to help the main ingredients, wood flour and plastic, bond together firmly,
  • UV stabilizers such as carbon black and titanium oxide, which help protect the material from damage by ultra violent rays, at least for a time,
  • Biocides, the most common being zinc borate, to reduce mold, mildew and fungal growth,
  • Plasticisers such as Wollastonite and calcium carbonate that add resiliency to the material, making it less brittle, and helping it to better resist impact. damage.
These "additives" make up as much as 5% of the composite by volume. Most of these are harmless, but some are not. Carbon black, for example, is often added to the deck mixture to combat ultra violet degradation. It is a suspected carcinogen, and if inhaled, a visit to the doctor is usually recommended. You probably won't encounter it in inhalable (dust) form, but your installer just might. It is usually not possible to tell from the manufacturer's colorful brochures what additives the decking composite contains, and if any might be harmful to you or the environment.

Sherwin-Williams Exposure Testing

Here are some results from a Sherwin-Williams study of what happens to composite decking after years of exposure. The pictures tell the whole story.

Images courtesy of
The Sherwin-Williams Company, Inc..

How Much Wood, How Much Plastic?

It is also important to know how much wood, and how much plastic is in the mix and which plastic is used. Is it a relatively environmentally benign plastic? Is it a stiff plastic that adds some structural rigidity? A composite deck that contains more plastic is less prone to fading and will not as easily support the embedded mold and mildew that has plagued some high-wood-content composites such as Trex. But, keep in mind that the more plastic that is in a composite the more it acts like plastic and the more problem you are likely to have with heat retention and seasonal movement which can cause excessive gapping between boards.
The type of plastic is important. Almost all composites contain polyethylene, but polyethylene comes in high-density and low-density formulations. High-density (HDPE) is stiffer and resists wear better. Polypropelene is better than polyethylene, but also much more expensive, and poly-vinyl chloride (PVC) the stiffest and most wear resistant, but not only expensive, but an environmental hazard during manufacturing that continues to off-gas dangerous chemicals for as long as several years — good thing decks are outside. Although none of them are particularly eco-friendly, polyethylene is the greenist of the plastics, and PVC by far the most dangerous.
As a rule of thumb, you don't want more than 60% wood filler in a composite decking board. Any more than that and the plastic binder has a hard time encapsulating the wood flour, leaving some of it exposed to the elements. The size of the word particles is also important, smaller is usually better, but also more expensive. The type of pigment used has an effect on how much your decking will fade. Organic pigment are very likely to fade a lot, while non-reactive chemical colorants fade more slowly and keep their color longer.

The Material Safety Data Sheet

Where do you find out how much of what is in a composite deck? Ask your decking supplier for a Material Safety Data Sheet. All manufacturers must have them by law and must give them to you when you ask. Many companies publish their MSDS sheets on their web site. This disclosure will not tell you everything about the composition of the material, but will usually tell you how much wood fiber and plastic it contains, and whether it contains any potentially harmful additive. And, as a bonus, it will often disclose how much wood and plastic is recycled waste.
How much is disclosed in an MSDS, however, varies widely. Some companys reveal very little. Trex, for example, lists some of its ingredients, but does not disclose how much of each ingredient is contained in its composites. It is particularly secretive about the formulation of its capstock shell used with its Transcends products. It will not even disclose which plastic or combination of plastics is used.

Is it Color-Fast?

Composite manufacturers have been beat up pretty bad over fading, so most now will cheerfully provide samples or at least images of their decking after three to six month's exposure. These are the colors you want to rely on, not the new-out-of-the-box colors. New colors may last as little as 90 days. But, don't stop there. You will also want to know what the decking will look like after three years. And, that's where the research gets a little more complicated.
No manufacturer has samples that will show you what the decking will look like after three years — or thirty years. Testing organizations like Consumer Reports are conducting tests that look at, among other things, color changes over time. Coatings manufacturers like Sherwin-Williams have already finished testing some of the composites, and the results are not encouraging. After three years, most un-capped composites tested were gray or nearly gray. Unless that is your preferred aesthetic, you will want to select decking that holds most of its color for many years. Unless you can find an actual deck of the proper age to look at in your area, your best source for information about fading is, again, the manufacturer's warranty. Companies that are confident that their decking will not fade significantly show that confidence in a guarantee against fading in their written warranties.

Railings and Accessories

Unless you are going to buy another manufacturer's railings, look at the complete cost of the deck, including railings. Decking is a highly competitive business. Many manufacturers sell their deck boards at barely above costs, expecting to make up any loses by selling the matching railing and trim accessories. Railings and accessories are where manufacturers make their big profit.
Most companies will have you believe that you must buy the manufacturer's accessories to get an exact color and texture match. That's not true necessarily, but it is a chore to do the research required to find a compatible railing system made by another manufacturer, and then it is often not much cheaper.
Also keep in mind that many decking manufacturers do not actually make their own railings. These are farmed out to other companies, and the color and texture match may be much less than perfect. Look at actual samples, not just pictures when trying to match railing and accessories to your deck choice.

The Deck Structure — Does it Need to be Stronger?

Find out if the decking requires a beefed-up under-structure. You can find this out in the manufacturer's installation instructions, usually available at its web site (but you may have to pretend to be a decking professional to see them). These usually specify the maximum spacing of deck joists needed to adequately support the composite decking — typically 16".
But, don't stop there. Keep reading and you may find that a 12" spacing is "suggested" for a greater feeling of "firmness". This means that while a 16" spacing will result in a deck that won't fall down, a 12" spacing is going to result in a deck that feels less flimsy. But, even if the decking is stiff enough to span a 16" gap when new, this may not be the case in a few years. There is some evidence that after composite decking goes through several seasonal freeze/thaw cycles, it looses a significant amount of stiffness. A study conducted in 2005, for example, found significant loss of stiffness in composites with a high wood filler content after just two cycles. The loss of stiffness was attributed to decreased "interfacial adhesion" between the wood flour and the rigid plastic binder.1
Give preference to decking that is firm enough to allow a standard 16" joist spacing. The downside: firmer composite deck boards often contain a high proportion of vinyl (PVC) which is considered less environmentally friendly that the usual plastic, polyethylene.

Proprietary Fastening Systems

If the decking can only be installed using the manufacturer's proprietary fastening system, factor the price of the system into your decking cost. Some of these systems are quite expensive. Some are difficult to use and require special tools. And, some are only sold to professionals with special training.

Evaluation Reports

Composite decking materials are required by most local building codes to tested and evaluated before they can be used to build a deck. The results of the evaluation are presented in a report called either an Evaluation Service Report (ESR) prepared by the International Code Council Evaluation Service or Code Compliance Research Report (CCRR) prepared by Architectural Testing, Inc.. The report will tell you such things as the type of structure needed to support the composite decking, its fire resistance, whether it can be used on stairs, and so on — the type of information that a building inspector uses to determine whether the deck has been built as the evaluation engineers specified, and information you can use in deciding whether a composite is a safe and reliable product.
Usually, you can get the manufacturer's evaluation report just by asking for it, or you can look it up on on line. Read it carefully. It will often contain valuable information about the composite that does not appear in the manufacturer's literature.

Commercial Use

Many composite manufacturers do not guarantee their products for commercial use. Some even state that their decking is for residential use only. If the manufacturer cannot certify its product for heavy-duty commercial use — all other things being equal — skip that company and go with a company that has a little more confidence in its product.

1. Pilarski, Jeanette M., and Laurent M. Matuana. "Durability of wood flour-plastic composites exposed to accelerated freeze–thaw cycling. Part I. Rigid PVC matrix." Journal of Vinyl and Additive Technology 11, no. 1 (2005): 1-8.

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