This is a major renovation of an old office building. The new building will use structural walls and metal roof of previos building. That building had no insulation on roof, it was just a metal roof, and the walls were 6" concrete block without insulation. According to ashrae if the previous building was also conditioned, any alteration not need to comply with the standard. So my firs question is, should I model the baseline as it was without insulation, and then take advantage of the insulation of the proposed building?? Second question, how do I document that the previous building was conditioned (with mini-splits and wall-units). There are just structural walls and roof at this moment.

Third question has nothing to do with previous, according to Ashrae you should not model ceiling. My understanding is that this restriction is just for baseline, right? Can I model ceiling in the proposed?

Thanks