Which is greener: cedar decking or a composite like Trex?
15' x 30' deck
I wrote a response to a similar question in 2011 regarding the comparison between Trex composite decking and wood and heard back from the homeowner that she decided to install a wood deck. Please take a look at that Q&A (here) to see where we were on this question two years ago.
In updating my analysis to answer your question I did some research on what developments have been made with composite decking.
My main observation is that composites have strayed from using recycled content, their original green attribute.
Composite decking was first introduced in the 90s by Trex who developed the initial idea of a composite made from 95% recycled sawdust waste and used plastic bottles (HDPE) where the wood fibers act as reinforcement for the recycled plastic.
They initially offered a very basic product in a few colors that were easily achieved. Overtime composite wood has developed into a huge industry with a variety of new products that profess to look like natural wood – that never fade and require no upkeep, and on top of that, are environmental saviors.
A National Association of Home Builder’s (NAHB) research report (here) speaks of the benefits of composite lumber:
- its efficient use of materials and non-toxicity.
- Composite wood is not subject to decay, splintering and warping.
In contrast, wood for exterior use is often treated with toxic chemicals when it is installed in high moistures or contacts the ground to prevent decay. It also requires refinishing.
PVC in composites
The NAHB report also states that that “recycled wood/plastic composite lumber typically consists of a 50/50 mix of wood fibers from recovered sawdust and waste plastics that include high-density polyethylene (HDPE), PVC and others.”
This quote brings us back to my previous concern that PVC is now becoming part of manufacturer’s formulations.
So if you choose to go with a composite wood product, check with the manufacturer for the ingredients in their product and how they have achieved colors that do not fade over time.
For example, I found a product (here) which is less self-conscious of its non-environmental aspects, and openly advertises that their “PVC engineering guarantees the ultimate in scratch, mildew and stain resistance, with a 25-Year Fade and Stain Warranty.” Their decking and railing is also advertised as having only 51% recycled content.
Recycled content and recyclability
Another “plastic lumber” product was advertised as recyclable. This seemed a brilliant development as the criticism of composite wood is that it is a “monstrous hybrid.” That is, a mixture of materials that can never be separated, and once finished with its useful life, will go into the landfill where it will last forever.
- With more reading I found that only 50% of the plastic they use is recycled and of the recycled content only 10% is post-consumer.
- This means they are manufacturing with: 50% virgin plastic, 40% manufacturing scraps, and 10% waste product.
- I called the number listed for “how to” recycle the product (here). The technical person was dumbfounded that someone was actually calling on this, and said that they haven’t recycled any of this. After some discussion I was told that it would need to be sent to a specialty recycler, and if I couldn’t find one in my area they would arrange it to be shipped by Fed-Ex to Illinois.
Another product new to the market is bamboo composite decking. The manufacturer advertises their product as the ultimate in composite decking. It is made from 60% renewable bamboo fibers and 40% recycled HDPE plastics making it 3X’s as strong as composite decking.
Their website discusses in length the environmental (and design) attributes of bamboo. Again the essence of the environmental aspects of this product is lost. This company is shipping virgin bamboo across an ocean and combining it with our waste, where it will eventually end up in our landfills forever.
Trex may be one of the better manufacturers of this product but again there is green-washing in their marketing. I looked up their MSDS (Material Safety Data Sheet) for the content and they list Wood Fiber at 50-60%, Polyethylene (HDPE) at 40-50% and Carbon Black at <1%.
Elsewhere they say that there is 95% recycled material. What is the other 5% and why do they list all of the sources for the wood fiber dust and list nothing for the polyethylene!
Since my last article I have spoken to a window manufacturer who said that they provide Trex with their proprietary coating “Transcend” and that it does in fact have PVC. It would give Trex so much credibility if they would just list the percentage of PVC in the coating, which is most likely minimal.
From a design perspective I prefer the composite wood decking without the coating. The grey color seems the most appropriate as one isn’t immediately confronted with the fact that it is trying to look like wood. A green friend of mine purchased grey Trex with a coating (because he couldn’t find one without) and installed it upside down because it looked so artificial.
The examples are endless. The marketplace has clearly recognized that ease of maintenance and green sells.
It is up to us, the consumer, to sort through all of the green-washing and challenge the manufacturers as to what materials they are using and if they meet the environmental integrity they are marketing.
If you choose to go with wood, Cedar is a good choice as it is similar to redwood in its durability, and its resistance to decay and insect pests. Typically it is not used as a structural member because it is weaker than redwood, but it is fine for decking. It is fairly moisture resistant and will fade to a grayish tone if left untreated. As you probably know it is half the cost of redwood.
Your environmental concerns will be addressed if you purchase Cedar that is certified by an independent, third party forest certification program. Look for the CSA (Canadian Standards Association), SFI (Sustainable Forest Initiative) or the FSC (Forest Stewardship Council) labels.
Although there are tropical woods from sustainably managed forests that are harder and last longer, such as Ipe, and Mangaras, using a wood that is produced in North America is the appropriate direction to take.
For more information:
Read "We’re trying to figure out what type of wood to use for an outdoor deck. Any advice?" a Q&A answered by Jim Zack.
Read This Old House's overview of composite decking here.
Check the University of Minnesota's website for advice about selecting wood for outdoor structures here.