At our office, we have a server room located on the southeast-ish side of our building, exiting onto a parking lot/loading dock area (a completely paved area with zero shade). The door is an emergency exit (made of steel I believe) with one of those bars you push to open the door. And the door is completely exposed to the sun for most of the day. The rest of the exterior wall is concrete. We keep that room closed because it contains sensitive hardware and some sensitive files.
On hot days (like yesterday), that door gets hot - like, you can't touch it with your hand hot. And the server room gets uncomfortably warm as well, because we have this metal door radiating into the room. And occasionally, we have hardware issues as well - we have a "disaster-proof" NAS in there that overheats and shuts down (because it's insulated to protect against fire damage). We do have a dedicated air conditioner in there which can usually handle the heat, but once in a while it just gets overloaded.
I should note that the landlord will not permit major renovations, and that's probably not an expense we need right now. Also, this happens maybe two or three times a year, so it's not a huge issue, but it would be nice to correct if we can do it inexpensively. I have thought about perhaps sticking some fiberglass insulation to the inside of the door, but that's going to be ugly, kind of messy, and probably not something management will go for. Something like styrofoam might work as well, but I suspect actual styrofoam would not be an adequate insulator.
Is there something we can do to cheaply and easily insulate the inside of that door so it's not radiating so much heat into the room?