The most correct would be to exactly mimic reality. your building. To do this, you might consider the inside dimensions for volume (as your air barrier is on the inside I imagine), then use center line for your exterior wall areas (for thermal transmittance).

The most correct is not always the easiest, so for this reason there's usually some agreed upon convention to make your life easier as an energy modeller.

I have seen technical documents that recommend any one of the three methods (center line, inside, and outside), so I'm sure you could argue any of these to be acceptable practice. Keep in mind that using outside dimensions will be conservative from a total energy use perspective.

Hope this helps.

The most correct would be to exactly mimic your building. To do this, you might consider use the inside dimensions for volume (as your air barrier is on the inside I imagine), then use center line for your exterior wall areas (for thermal transmittance).

The most correct is not always the easiest, easiest or most intuitive, so for this reason there's usually some agreed upon convention to make your life easier as an energy modeller.

I have seen technical documents that recommend any one of the all three methods (center line, inside, and outside), so I'm sure you could argue any of these to be acceptable practice. outside) dimensions. Keep in mind that using outside exterior dimensions will be conservative from a total energy use perspective.perspective, so that might be your best bet.

Hope this helps.helps.