Styrofoam Insulation

I inspected a home built in the early 70s today and the crawlspace had 1/2" thick 4x8’ Styrofoam insulation installed to the bottom of the floor joists. Am I right to assume this is not a correct application because moisture/condensation can be trapped between the floor joists? Also I’ve heard of fire hazards with Styrofoam insulation. There was no crawlspace access. By removing some of the wall vent covers I was able to observe the crawlspace.
Thank you for your help,
Steve D.

Styrofoam burns well and gives of a hazardous gas . It must be covered .

Doesn’t matter if it’s covered or not. Insulation has to meet a specified flame spread index, even in concealed spaces.

"IRC R302.10.1 Insulation. Insulation materials, including facings,
such as vapor retarders and vapor-permeable membranes
installed within floor-ceiling assemblies, roof-ceiling assemblies,
wall assemblies, crawl spaces and attics shall have a flame
spread index not to exceed 25 with an accompanying
smoke-developed index not to exceed 450 when tested in accordance
with ASTM E 84 or UL 723.

  1. When such materials are installed in concealed
    spaces, the flame spread index and smoke-developed
    index limitations do not apply to the facings, provided
    that the facing is installed in substantial contact with
    the unexposed surface of the ceiling, floor or wall finish.

  2. Cellulose loose-fill insulation, which is not spray
    applied, complying with the requirements of Section
    R302.10.3, shall only be required to meet the
    smoke-developed index of not more than 450."

Confuse if there is no access how did they get 4x8 sheets in there ? Been there since the 70’s?
Just be sure it is what you think it is