You need to define what volume you need and for what purpose. Some possibilities:
- total volume to determine if a professional has to stamp the design : this would include the total volume measured from outside of enclosure and includes volumes of walls, floors (it isn't just the actual room volume)
- volume of rooms only (this would exclude volume of walls etc. and the above mentioned room schedule should work)
- include or exclude plenum and other intentional voids like shafts in a building?
Without knowing what volume you need and for what, it is hard to answer how to get the correct number. Same goes for area calculations where walls and void spaces could be included or excluded.
Edit: there seems to be a website issue preventing me to have space between paragraphs
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