because the building is complex i am using
walls + a polyline as a zone boundary for the gross area in the same layer as a the zone and when i want to
update the zone using design> update zones command.
But then i realised the zone was not calculation the entire zone but was subtracting a part from some walls in a hidden layer.
Only when i switched to manual construction method did it displayed the right area.
Is this a bug?
Because i though when updating a zone with a few elements visible only those elements would affect that zone.
I think there are different types of zone area calculations - measured, reduced and calculated. Calculated is definitely applies all additional reducing percentage rules, when measured just shows what it is. Try to look to that too and what differences in numbers between them you are getting.