I recently moved into a two-story home that has a storage cupboard under the stairs. There is no finish underneath the bottom part of the stairs, and the bare plywood is exposed, which is a fire safety hazard (since a fire that got into the cupboard could easily ignite the stairs and make it impossible to exit the home via the stairs).
Current building code in my area calls for the underside of the stairs to be protected by a sheet of drywall to protect the wood from direct exposure to flames. However, I'm looking for a quicker and cheaper temporary solution as a holdover while dealing with other important upgrades and renovations.
I noticed that the reflective bubble insulation at my local hardware store has a Class A fire rating, which is the same rating as drywall. It would be very cheap and easy to staple sheets of reflective bubble insulation to the diagonal framing (strongback?) along either side of the stairs:
My understanding is that the purpose of putting drywall under the stairs is not to make them fire-proof (which is impossible with wooden stairs anyway), but to make them fire-resistant for long enough for anyone on the second story to safely move down the stairs and exit the house. Although it doesn't precisely meet the building code, is reflective bubble insulation with a Class A fire rating a reasonable temporary solution for protecting the underside of plywood stairs from direct exposure to flame?
One possible consequence I can think of when compared to drywall is that the reflective insulation might trap more heat in the cupboard and increase the speed at which the cupboard reached flashover temperature.