I've probably asked this on here before, but then the weather got warm
and I got busy with other stuff and forgot about it.

I have an old abandoned buried garage bay in basement, not used since
they added a first-floor 2 bay garage, and filled in old garage door and
driveway cut in front yard. 12-18 inches of the poured concrete is
exposed above grade, so the space is cold, now that winter has returned.
(Floor above and dividing wall are insulated, badly.) It is also on the
damp side, but by changes to gutters and planting beds I have eliminated
the actual active leaks (knock on wood.)

I would like to insulate the walls on inside, since house isn't worth
digging up the outside to do it properly. Due to the dampness, I want to
avoid drywall, but all the foil-face foam boards say they have to be
covered by drywall. I also didn't really want to go to the expense/labor
of studding out the walls. My plans were to hang foam sheets like a
curtain from sill plate, with maybe a few dabs of adhesive at bottom to
keep them from flapping around. But how to provide the code-required
firebreak, and also provide a path for any future leaks to drain down to
floor level? (I was going to hold the 'curtains' off the floor 3/4" or
so.) Does anyone make foam panels with integrated firebreak? If so, are
they affordable, and where can I get them?

Is there an obvious answer I am missing here? With the repairs and
upgrades I have already done, I have as much money into this place as I
could sell it for, under current market conditions, so I am looking to
do this on the cheap. Space will be storage/quasi workshop only, so it
just needs to be safe and legal, not pretty.

aem sends...