Substantial Renovation - Envelope Modeling

Hi, I am modeling an existing school building which is undergoing substantial renovation. As a part of the renovations, new windows are being added and the grade level is being changed. Per Appendix G, it seems like the window area for the baseline will need to the total prior to the renovation changes (in this case, baseline area will be lower than proposed). Is this interpretation correct? Also, should the grade levels be different as well? This means exposed wall area will be different between baseline and proposed building. There will be more below grade walls in the baseline as compared to the proposed case. Thanks in advance.