I have tried zoning an office building in 2 different ways, with the same building, E+ reports building area in 2 different ways.
This first solution shows total floor area, this is good:
This second solution shows ground area only, in case building 4 storey, result was the same, it shows ground area only.
This isn't a bug, just regular behavior of OpenStudio/EnergyPlus. In EnergyPlus, the concept of OpenStudio Spaces doesn't exist. Only thermal zones matter.
So historically in OpenStudio if you model separate spaces and include them in a single thermal zone, the area from the upper space is excluded of the building Floor Area. According to this answer, "OpenStudio does this for any interzone floor/ceiling surfaces whether they have an air wall construction or not".
I just tested in OpenStudio 1.9.0 (Release candidate), and it is still the same behavior. I applied a single zone to two spaces right above each other in the Sketchup plugin, and then I used the "Surface Matching Tool", and OpenStudio did exclude the top space.
Note that using the Surface Matching tool is very important to have this behavior, if not matched, the area of the top space will still be included (but your heat transfer will be wrong).
You could set the ceiling of the space below and the floor of the space above to Adiabatic (and assign construction) and it will count the area of both, I just checked.
this issue does not occur when I draw zone manually, it happens when OS generates building from sketch, using "create space from diagram" tool.
I created the above example using 'the create space from diagram tool'
What version are you using? 1.8.0? Also, have you tried checking if your upstair space indeed has "Part of Total Floor Area" to 'No'?
Yes, I use 1.8 but 1.8.5 and 1.9 has the same thing. The option "part of total floor area" set to "yes". Sorry, this thing happens when I made multistorey building, using "create space from diagram". It means, generate >=2 level, not only create just 2nd floor.
I got it. It's not because of using the create space from diagram, it's because of surface matching. If you match surfaces before running, it does exclude the top floor. So it's still the same behavior as before
If this is a functionality that you see a need for may want to add it as a feature request user voice. One solution is for the forward translator to look at the ceiling/floor construction. If it isn't an air all (e.g. you are not modeling an atrium) then we could set the proper zone area counting all floors. A lighter weight change would be to expose in the API the ability to set the zone floor area field. Then the functionality described above could be in a measure.
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Im not sure the different area results make change other result or not, like EIU number..
@luntinfr : I've edited your message to include the pictures directly instead as links and reordered them as I understand your problem. If not correct please redo.