How to install PVC 4x8 sheets on a ceiling
 

I'm putting PVC 4x8 sheets on the ceiling outside to a front door (alcove). After their installed, tongue and grove boards will go on the side (vertically). When I install the ceiling I will use construction adhesive to go against the joist. My question is how do I go about nailing? My initial thought was to use a trim gun and making sure the setting didn't blast through the PVC sheets. But I'm a little concerned that may not work. The reason I'm using PVC is to create less maintenance in the future. I will never have to replace the sheets unless they crack, all I may have to do is repaint.

PVC or FRP? Predrill if cracking is a concern.

PVC. U can't predrill if you are using a trim gun. What are you suggesting by predrilling?

This should be vented soffet, no mainantence and better yet no rot do to no venting.

Not trying to second guess, but why do you want to use sheet material? You say you want to use a trim gun, how will you cover exposed the nail heads? I'd suggest using vented soffit material or the same material you use on the side wall. Just my :2cents:

I want a clean look. When using a trim gum the nail heads sit below the surface so I would puddy over the heads. I'm using PVC do there are no worries of rot.

The rot will be caused by using a solid surface and trapping moisture inside. If this construction is with permits, ask advice of inspectors before sealing this up, and if it is without permits, get some good advice.

We're not worried about rot to the surface material, our concern is the substructure you are sealing up.

I'd be using beaded hidden vent soffit material up there. It would look so much better then a flat sheet.
If you did go with PVC sheet I would be using 1/2 thick attaching on the outsides and around where the light goes with screws then add some form of crown or cove moulding to cover the screw holes.