Here’s a review of composite decking from Howard B. As you’ll read, his deck isn’t even a year old, and it’s already exhibiting some serious problems:

We have a TimberTech “Earthwoods Evolution” deck at our new home. Within two weeks of installation, we began to see downward “bowing” near butt joints. This is about 7/32″ deep, with the deepest point about midway between the joists (16″ centers). The problem is progressive in the sense that it has spread to more boards, and it is also starting to appear farther from board ends. It is now about twelve weeks since installation…I’m a recently retired engineer, and my own theory is that this capstock material is absorbing moisture through the ends, which is causing swelling. With the boards firmly anchored on 16″ centers, it would not take much increase in board length to cause a significant bow Seems to me that this would be a common problem, but I haven’t yet seen it discussed or shown on-line.