I recently installed some HVAC zone dampers in ductwork located in my garage. To do this I needed to remove the existing fire rated sheetrock ceiling to get access to individual ducts. With that work now completed I need to replace the ceiling but want to maintain easy access to the dampers in the event they later need to be repaired.

Since all (8) dampers are essentially in the same 15 foot linear path I thought I would install some sort of hinged 3'x16' access panel along this area to provide easy access. I want to maintain the fire rating for the garage ceiling so I'm interested to hear any suggestions for materials other than drywall panel to make up the surface of this access panel.

The overall enclosure I would construct would surround the main HVAC distribution duct which is parallel and just off center of the garage bay. I’m envisioning the bottom portion to be hinged to provide the access. My biggest limitation is with the garage overhead door open I only have about a 1.5" clearance between the overhead door and the existing duct. With the door closed, I have free and open area to swing the panel open. I'd prefer the access panel to be some rigid but of manageable weight.

I've considered a melamine panel but I'm not sure if it has sufficient fire ratings (comparable to 5/8" drywall).

Any thoughts or suggestions are appreciated.