There was a great article in today’s San Francisco Chronicle about composite decking versus traditional cedar and redwood decks- “All Decked Out”.
Essentially, there are three drawbacks to composite products according to the article. Composite decking products are susceptible to mold, fade over time, and are susceptible to staining as well. The advantage to these materials is less maintenance and a longer useable lifespan.
I would add two other problems with composite decks. First, the composite materials do not have the same structural properties as wood. As a result all the structural framing (and sometimes railings) for the deck will need to be constructed out of regular lumber which will have a shorter lifespan than the decking boards above it. Second, the composite materials, while much improved since their introduction, do not replicate natural wood’s appearance.
One final issue that the article points out: composite decking is not biodegradable. While it is true that composite decking is made of a high percentage of recycled plastic (such as grocery bags) and wood waste (saw dust), once the decking is disposed of after its useful life, it will be sent to the landfill where it will degrade at the same rate as other plastics. Natural wood on the other hand will rot and degrade naturally.