As I see it the major issue with this credit is the 75% threshold in MR 1.1 &1.3.

Consider two possible assemblies.
- A 1920s 18" thick historic masonry and terracotta facade
- An 1970s gypsum board and metal stud partition

Under the methodology for calculating the credit I should include area for BOTH SIDES of the metal stud partition wall but only one side of the masonry wall, in effect giving the 1970s stud twice the weight per square foot as the historic wall.

Similarly a sheet of carpet or vinyl flooring has the same weight as a concrete waffle slab.

Similarly, I do not believe that historic buildings should be heavily penalized for removing non-historic interior elements & finishes, especially for those projects which have gone through review by NPS.

Perhaps some kind of a matrix which includes depth of the item as well, to calculate volume. USGBC/GBCI could set default widths for things like carpet (1"), interior part ions (6"), etc to simplify the calculations. Believe me, having done MR 1 credits on several projects I realize it will be a pain, but when combining MR1.1&1.3 I don't know how else you do it fairly.