Hi Allen and all.  The big issue for top bar hive (tbh) use in the northern
areas is "Can the bees winter over in top bar hives?"
 
As I see it there are three things to note:  First, there must be adequate
food reserves, as usual.  In a tbh that could mean 12-15 combs mostly full
of honey.
 
Secondly, the cluster must be able to use this food!  Question is, will
they move horizontally, or will they just eat what food is above them til
they hit the top-bar, and then starve?  Maybe we can facilitate horizontal
migration "down the hive" by supplying communication holes through the
combs, to maintain cluster integrity.  This is something I will try next
winter.
 
Finally, ventilation is a requirement, so that moisture doesn't build up
causing soggy (deadly) conditions and frost in the hive.  Perhaps the top
bars could be separated a tiny bit at certain intervals to allow for
ventilation, and through ventilation provided above the bars.
 
As I have related to some in the gang, I have overwintered top-bar type
hives here with great success.  However, they had upper stories of honey (&
bee space between the bars) so the bees just moved upward as they normally
do over winter.
 
Commercial tbh beekeeping?  Hey , the initial investment would be low.  The
comb honey would indeed be tops for the consumer, with the natural (thin)
midrib, and more honey per volume of wax.  Even with "thin super"
foundation, comb honey from frames can be overly "waxy."   Seems to me
anyway.     Regards,   JWG