Air sealing steel I beam

This one is a forum question, not a finished project or product news, so there isn't a takeaway that applies broadly to homeowners. A homeowner posted asking how to air seal around a steel I-beam that runs through their ceiling, where the beam sticks down below the ceiling joists into the living space. Air sealing means closing gaps so indoor air doesn't leak into the attic, which wastes energy and can cause moisture problems.

The homeowner is redoing their ceiling drywall and plans to use 6-mil plastic sheeting as the barrier against air and moisture movement. On one side of the beam, the ceiling joists rest on top of it; on the other side, the joists run alongside the beam without touching it. Rather than simply wrapping the plastic around the beam, the homeowner wants to treat the top of the beam itself as the sealed boundary and questioned how best to do that, since the beam will eventually be covered with drywall.

At the time this was posted, no answers had been given yet. If your own house has a steel beam or similar obstruction poking through a ceiling or attic floor, it's a reminder that these transition points are common weak spots for air leaks, and worth paying attention to whenever you're opening up a ceiling for insulation or drywall work.