What does "Barbette" include?

[Buchanie]

I notice in the academy that although my ship has no raised gun platforms for superfiring, or elevating the turret a deck higher, if I choose to select "barbette" under the armour menus it causes the weight of my ship to increase.  Do I assume then that the "barbette" is the whole of the armoured cylinder from the turret all the way down to the shell rooms?  If it is only a raised gun platform above deck level, then this increase must be an error - or maybe it refers to the portion of the cylinder above main deck where the hull has a raised foredeck?  Just as the turret should include the whole of the turning column, all mechanisms for lifting ammunition up from the shell rooms etc. rather than just the gunhouse at the top - so similarly the barbette should include the armoured cylinder below the gunhouse inside which the whole turret revolves, and not just an externally exposed gun platform above deck level.  1870s RN produced so-called barbette ships where there were no turrets, big guns sat in the open on top of barbettes - but meanings move on, and "barbette" has modified its meaning by the time we get to 1900 - but we still refer to the raised gun platform as a barbette.  Can you clarify the point for me - why the increase in weight when I'm designing for "armed convoy attack"?

Edited March 24, 2020 by Buchanie
it wasn't complete ... mistake!