i tried some stuff about the walls and i found some stuff but let me tell you first about a bug in VW 11.5 that i found a year ago:
if you make a connection between 3 walls with an L and a T connection, the volume calculated in the worksheet gives you 0,000000000xxx. so that was the big problem in my calculation program i tried to make.
this problem is solved in VW 12, although there is still something wrong with it! that's what i found out now, so here it comes:
*if all your walls are not joined in any way, the result is correct.
*if you join walls from the same thickness in any way, the result is correct.
*if you join walls from different thickness in any way, the result is not the same. although the difference is minimal
so the fact is that there is no bug or a faulty thing in it.
it is just how those functions calculate. if you take the volume/thickness, you'll get the correct result. the functions like wallarea_gross etc. uses the center line of your wall, and if you look at the connection between walls, you'll notice that the end and begin points change when you make your connections. the worst is with a 3way join with walls of different thickness. so the minimal difference between the results of volume/thickness and wallarea_net is because of wallarea_net uses the center line from begin to endpoint.
i hope it's understandeble.
maybe you could send the file to me? then i can take a look at it?