What is the VOLUME of COMMERCIAL buildings in the US that have
"dropped ceilings" (that is ceiling tiles in a 't-bar' (also known as
'hung' or 'lay-in' ceiling')) that ALSO have insulation laying on top
of the dropped ceiling (that is batts of insulation laying on top of
the ceiling tiles to prevent heated or cooled air (via an HVAC unit)
from leaking from the "conditioned space" to the "unconditioned
space")?  Please provide as much quantifiable information as possible.