||07-13-2008 08:09 PM
You should use what the manufacturer stipulates.
PVC materials have a greater rate of contraction and expansion than wood. Most major PVC composite brands stipulate a full-head nail, because of this.
Now, aside from that...We have always used 15g and 16g stainless steel finished nails (using pneumatic finish nail guns) to attach PVC material. We then install stainless steel trim head screws at all seams, corners, and transitions (sinking heads slightly). We have never ran into issues of material separating from the sheathing, or pulling the fastener out.
Based on that, my suggestion is to use either Stainless (always the best choice) or galvanized and caulk over the fastener (suing appropriate caulking for PVC materials).