I while back, I built a small building in my backyard with a roof that was framed with 2×12 joists (framed dead flat), a 3/4” plywood deck and tapered styrofoam insulation on top of that. The roof itself is PVC.  At the time I built it, I anticipated the possibility of putting in a kitchen later and installed a roof jack where the range hood would go. Fast forward several years, and I am now ready to put in the range hood.

I am wondering how to best make the connection to the roof jack. Do I need to remove the roof jack and install another one? I guess I’m struggling with how best to make an air tight connection between the roof jack at the (flex?) duct that will be attaching to it. I have included a few shots to better describe the situation. Any help is greatly appreciated. Maybe the connection between the jack and the duct doesn’t need to be so air tight? I just want to do it right and not inadvertently commit a no-no do to my lack of experience with this particular build.