We get a couple of calls a week for composite pergolas. "Serves us right for making our pergolas look so flawless". People see the solid stain and tight joints and they often assume they are cast from plastic.
The fact is composite and PVC have aspects that make them unsuitable for building any structure that is in any way structural.
PVC products, (like siding, and plumbing materials), tend to get brittle when exposed to the sun for extended periods. In a place like Florida you will have a hard time finding an engineer to stick his neck out and stamp plans for a pvc pergola--and everything built in Florida needs an engineer's approval.
Here's a pergola hidden within a now defunct composite decking plant's yard...obviously not attractive enough to show in public. It even looks askew--and watch that last riser, looks like a killer.
Composite products have not been as wonderful as we all hoped. "Maintainance Free", turned into "Low Maintenance" after a few law suits. Recently those containing recycled wood and recycled plastic have been breaking out in mold spots that grow from the interior out, and troubles with disintegration, "Flaking".
There are a few new products, however they all have issues with weakness when heated, so without solid wood or metal within the structure they simply won't take high temperatures, wind or stress of any kind.
The last tragic issue has to do with fastening. It is difficult to make a secure connection from composite to composite, or pvc to pvc, (unless gluing--but even that lacks strength and doesn't look good with sleeves).
To create composite pergolas that don't have a metal frame or wood within will require designs that will change the look of composite pergolas. They won't look like pergolas as we know them--which means that they could be a hard sell.
If there are any composite companies looking to develop plans for composite pergolas give me a call and lets get moving on it.
For more about composite decking (click)