Base case and proposed case modeling

At he moment, we are modeling a buried building with a green roof (as part of the energy efficiency strategy) according to the appendix G of the ASHRAE standard 90.1 (2007) The question regards the base case and the the proposed one. The base case model must be buried as well? or it should be modeled as a regular building from ground floor, with the exposed envelope? Appendix G, table 3.1, "Modeling Requirements for calculating Proposed and Baseline Building Performance", section 5.- "Building Envelope" mentions both must have the same "total gross area of exterior walls". In section 5 of the mentioned standard, tables 5.5, regarding "Building Envelope Requirements for Climate Zone the item "walls" is composed by "Above Grade" and "Below Grade" Is it then, the total gross area resulting from the sum of "below grade" and "above grade" walls that should be the same for the base case and the proposed one? or, is it the below grade and above grade independently considered to equal the baseline and proposed case components?