I have witnessed an odd behavior this winter in a couple of my hives- the
bees have built partition walls across the opening in the center of the
inner cover, and in one case across much of the opening across the bottom
board.  The partition is thin, brownish gray, kind of like re-worked wax
with some propolis possibly mixed in.  I reverse my inner cover for the
winter, concave side down to allow the bees to "roll" over the frames
easily,and also leave a 3/8 inch shim at the top rear of the inner cover so
that the lid is pitched down in front.  This pitch is to allow any moisture
that condenses there to run forward and hopefully down the outer face of the
hive.
  Across the entrance I partially reduce the full height of the entrance
with quarter inch hardware cloth with all but 3/8 blocked with duct tape.
The hives in question erected their partition behind this, building up from
the bottom board to the inner face of the front wall of the hive.
  Has anyone tried using a goretex barrier membrane across the top of the
hive, one that would contain heat but at the same time allow moisture to
vent outwards?  It seems like it might work well as a partition, provided:
it is not too expensive, the bees do not interfere with it to alter its
property of allowing moisture to pass through, and also that no moisture
condenses on the inside of the membrane before being vented (and possibly
drain onto the cluster). I thought I might try something like this next
winter, on a few hives. /Curtis Crowell