I’m installing a Mechanical Fastened heat welded PVC roof on a small 40 x 40 office building flat roof that currently has torch down over hot tar on a car decking deck. Car decking is 2x6’s T&G, very strong. My plan is to tear off the existing roof and go with sloped 4 x 4 insulation panels and slope the middle (which now has standing water) to the drains/scuppers. My concern is inside the building has no attic, the ceiling is open and exposed. The tenant plans to use a drop ceiling and put batt insulation over the drop ceiling, or maybe in the bays of the ceiling joists where the car decking can be seen from the underside.
I don’t see much reason to vent, because there’s no air flow, it’s all open underneath. I’m worried about any condensation/water drip on the underside of the PVC sitting top of the foam panels on top of the car decking.
?? Should I use ice/water shield under the foam panels to prevent any water condensation from warm air rising up on the underside and cold air on the topside/outside? -Also we do get some snow in Seattle. Would that cause moisture on the underside? Vent vs. no vent? Maybe there’s another material I can put on the car decking to start off with?